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IEE Proceedings - Optoelectronics

Volume 151, Issue 5, October 2004

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Volume 151, Issue 5

October 2004

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  • Dilute nitride and related mismatched semiconductor alloys

    • Editorial: Dilute nitride and related mismatched semiconductor alloys
      Epitaxy and characterisation of dilute III–As1−yNy on GaAs and InP
      • Author(s): K. Köhler ; J. Wagner ; P. Ganser ; D. Serries ; T. Geppert ; M. Maier ; L. Kirste
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 247 –253
      • DOI:  10.1049/ip-opt:20040940
      • Type: Article
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      • p. 247 –253 (7)
        Epitaxial growth and characterisation of Ga1−xInxAs1−yNy films and quantum wells are presented. Starting with the epitaxy on GaAs, recent results on the local bonding of nitrogen in Ga1−xInxAs1−yNy are reviewed, revealing that bonding of nitrogen is controlled by an interplay between bond cohesive energy and reduction of local strain. Thus, III–N bonding can be changed from Ga–N to In–N by post-growth thermal annealing. For high In-content Ga1−xInxAs1−yNy on InP it is demonstrated that only small amounts of Ga are necessary to cause the bonding of the nitrogen atoms to at least one Ga neighbour. The epitaxy on InP substrates, equivalent to a drastic increase in indium content, allows an extension of optical transitions to longer wavelengths. The feasibility of high In-content Ga1−xInxAs1−yNy pseudomorphic quantum wells on InP is shown. The deterioration of the photoluminescence properties with increasing nitrogen incorporation can be partially compensated by thermal annealing. Within the resolution limits of the secondary ion mass spectrometry experiments, no annealing-induced loss of nitrogen was observed. The indium-rich strained Ga0.22In0.78As0.99N0.01 quantum wells are shown to exhibit room-temperature photoluminescence at wavelengths up to 2.3 μm. Finally quantum well lasers emitting at wavelengths beyond 2 μm are demonstrated.
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      Growth of GaNxAs1−x atomic monolayers and their insertion in the vicinity of GaInAs quantum wells
      • Author(s): M. Le Dû ; J.-C. Harmand ; K. Meunier ; G. Patriarche ; J.-L. Oudar
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 254 –258
      • DOI:  10.1049/ip-opt:20040889
      • Type: Article
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      • p. 254 –258 (5)
        The deposition of N-rich GaNAs atomic monolayers was investigated. Such layers were successfully grown while exposing a GaAs surface to a nitrogen plasma source during a growth interruption at 400 °C in a molecular beam epitaxy reactor. N accumulation was confirmed and evaluated by secondary ion mass spectroscopy. This process is compatible with regrowth, as in situ monitored by reflection high-energy electron diffraction. The crystal shows good structural quality, as displayed by transmission electron microscopy, that reveals that the accumulation occurred within 1 nm. In a series of samples, two of these ultrathin GaNAs layers were inserted in GaAs barriers, on each side of a GaInAs quantum well (QW). A drastic effect of the N-rich layers on the QW photoluminescence (PL) intensity was observed, as well as on the carrier recombination dynamics, with a strong influence of the spacer thickness between the QW and the N-rich layers. A time-resolved PL analysis of these samples evidenced nonradiative relaxation times in the range of a few ps. This very short carrier lifetime is attributed to the presence of nonradiative centres related to the N-rich layers close to the QW, and can be used to design ultrafast optical devices.
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      Surface rate-limiting steps and modelling of the nitrogen growth kinetics of GaAs1−xNx/GaAs
      • Author(s): H. Dumont ; Y. Monteil ; F. Saidi ; F. Hassen ; H. Maaref
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 259 –262
      • DOI:  10.1049/ip-opt:20040873
      • Type: Article
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      • p. 259 –262 (4)
        The growth features of the nitrogen incorporation into GaAs grown by metalorganic vapour phase epitaxy (MOVPE) are presented, with a comparison between experimental results and a kinetic model. The so-called ‘distribution coefficient’ of nitrogen varies in the range 180–1000 depending essentially on growth temperature. Experimental results were analysed with a schematic process of surface reaction kinetics for controlling the mass transfer. Some kinetic rate constants are proposed. The modelling of N incorporation at 520–560°C allows an identification of species coming from the DMHy thermal decomposition. Surprisingly, this study shows that the rate of N incorporation weakly depends on the arsenic precursor at low growth temperatures.
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      Structural properties of free-standing (In,Ga)(As,N) alloys
      Thermal annealing effect on 1.3-μm GaInNAs/GaAs quantum well structures capped with dielectric films
      • Author(s): H.F. Liu ; C.S. Peng ; J. Likonen ; J. Konttinen ; V.D.S. Dhaka ; N. Tkachenko ; M. Pessa
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 267 –270
      • DOI:  10.1049/ip-opt:20040941
      • Type: Article
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      • p. 267 –270 (4)
        Two kinds of dielectric films, Si3N4 and SiO2, deposited onto the surface of 1.3-μm GaInNAs/GaAs quantum well (QW) structures were studied upon post-growth thermal annealing. The blue-shift in photoluminescence (PL) as a function of annealing time showed distinct dependence on the selection of the dielectric films. It was found that a Si3N4 cap layer inhibits the blue-shift under specific annealing conditions and the blue-shift inhibition effect increases with the thickness of the Si3N4 cap; while a SiO2 cap layer enhances the PL blue-shift. X-ray diffraction (XRD) and secondary-ion-mass-spectrometry (SIMS) indicated that the enhanced blue-shift in PL from the SiO2-capped sample was caused by two factors: interdiffusion of Ga and In atoms across the QW interfaces and the decrease of N–Ga ion density (and hence N) in the QW material. Compared with the SiO2 caps, Si3N4 cap layers can inhibit both of these factors. Time-resolved PL decay measurements at room temperature were performed to study the optical properties of the uncovered and Si3N4-capped samples.
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      Composition fluctuations in GaInNAs multi-quantum wells
      • Author(s): M. Herrera ; D. González ; R. García ; M. Hopkinson ; P. Navaretti ; M. Gutiérrez ; H.Y. Liu
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 271 –274
      • DOI:  10.1049/ip-opt:20040930
      • Type: Article
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      • p. 271 –274 (4)
        GaInNAs/GaAs(001) multi-quantum wells grown by MBE at temperatures in the range 360–460 °C have been studied by transmission electron microscopy and photoluminescence. The authors have observed the existence of periodic contrasts with 220BF reflection, which appear more pronounced when increasing the growth temperature. These strain contrasts have been associated to composition fluctuations in the wells and, therefore, it is suggested that an enhancement of the phase separation in the GaInNAs quantum wells occurs when varying the growth temperature from 360 °C to 460 °C. The photoluminescence results show a broadening of the emission peak over a similar growth temperature range. Thus, the degradation of the optical properties in the GaInNAs structures is suggested to be linked to the composition fluctuations.
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      Distribution of nitrogen in GaInNAs/GaAs quantum wells
      • Author(s): D. Litvinov ; D. Gerthsen ; A. Rosenauer ; M. Hetterich ; A. Grau ; P. Gilet ; L. Grenouillet
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 275 –278
      • DOI:  10.1049/ip-opt:20040885
      • Type: Article
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      • p. 275 –278 (4)
        Quantitative high-resolution transmission electron microscopy was applied to determine the indium and nitrogen distributions in a GaInNAs/GaAs heterostructure. Two almost identical samples grown by gas-source molecular beam epitaxy on GaAs (001) substrates were investigated. The samples contained InGaAs and GaInNAs wells with the same thickness and In concentration. According to high-resolution X-ray diffractometry the average In concentration is 27% in both samples, with an N concentration of 1.1% in the GaInNAs quantum well. The evaluation of the photoluminescence peak position of the InGaAs sample and additional photoreflectance measurements yielded an In concentration of 30%. In-concentration profiles were obtained with the composition evaluation by the lattice fringe analysis (CELFA) technique for the InGaAs well using the chemical sensitivity of the (002) reflection. The averaged In concentration in the InGaAs quantum well was determined to be (30±1)% in good agreement with the other measurement techniques. The N-concentration profiles in the GaInNAs wells were measured by the comparison of the CELFA results in the samples with and without nitrogen. The N distribution is characterised by two maxima close to the GaInNAs/GaAs interfaces. The measured N concentration in the central part of the quantum well is (2.5±1.0)%.
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      Further insight into the growth temperature influence of 1.3 μm GaInNAs/GaAs QWs on their properties
      • Author(s): D. Jahan ; G. Patriarche ; V. Sallet ; J.C. Harmand
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 279 –283
      • DOI:  10.1049/ip-opt:20040888
      • Type: Article
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      • p. 279 –283 (5)
        The authors further investigate the influence of growth temperature (Tg) on GaInNAs QWs grown on GaAs. 7 nm-thick GaInNAs QWs were grown with Tg in the range 400–470 °C. As a first result, transmission electron microscopy clearly showed that flat interfaces are obtained for Tg lower than 450 °C. Beyond this temperature, the upper interface of the QW starts to undulate. Then the series of QWs was annealed at different temperatures. The PL emission of the QWs was blue-shifted and narrowed. However, it was noticed that these evolutions occurred at a lower annealing temperature (Ta) when a lower Tg was used for the growth. Even though the PL energies of the different as-grown QWs were the same, this observation tends to show that the nanotexture of the GaInNAs alloys depends on Tg in the range of temperatures investigated. The texture obtained at low Tg is more easily rearranged, by annealing, into a more stable configuration. This result is of practical importance for the growth of GaInNAs QW laser structures. By using the lowest Tg for the GaInNAs QWs, the AlGaAs cladding layer growth temperature (usually around 620 °C) is high enough to optimise the QW quality by its annealing effect.
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      Effect of fast thermal annealing on the optical spectroscopy in MBE- and CBE-grown GaInNAs/GaAs QWs: blue shift versus red shift
      • Author(s): N. Balkan ; S. Mazzucato ; A. Erol ; C.J. Hepburn ; R.J. Potter ; A. Boland-Thoms ; A.J. Vickers ; P.R. Chalker ; T.B. Joyce ; T.J. Bullough
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 284 –289
      • DOI:  10.1049/ip-opt:20040935
      • Type: Article
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      • p. 284 –289 (6)
        An investigation is presented of thermal annealing effects on spectral photoconductivity and photoluminescence in sequentially grown GaInNAs/GaAs and GaInAs/GaAs quantum well structures. Experiments have been carried out at temperatures between 30 K and 300 K. The results indicate that thermal annealing improves the optical quality of GaInNAs, but may cause either a blue shift, as commonly observed by other groups, or a red shift depending on the growth technique. The anneal-induced blue-shift behaviour can be explained in terms of two competing mechanisms involving the redistribution of nearest-neighbour configuration and the change of quantum well profile. The red shift is explained in terms of hydrogen-induced chemical effects.
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      Effects of electron irradiation on photoluminescence from GaInNAs/GaAs multiple quantum wells subject to thermal annealing
      • Author(s): E.-M. Pavelescu ; M. Dumitrescu ; T. Jouhti ; A. Gheorghiu ; N. Baltateanu ; M. Pessa
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 290 –292
      • DOI:  10.1049/ip-opt:20040879
      • Type: Article
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      • p. 290 –292 (3)
        Electron irradiation of a 1.3-μm GaInNAs/GaAs quantum-well heterostructure, grown by molecular beam epitaxy and subsequently subjected to rapid thermal annealing, is found to induce much stronger photoluminescence than that observed for an identical as-grown sample upon annealing. Annealing of the irradiated sample also causes an additional spectral blue-shift, reduces alloy potential energy fluctuations at the conduction band minimum, and narrows spectral linewidths. These irradiation-related phenomena are accompanied by a discernable change in X-ray diffraction features upon annealing, which indicate a change in quantum well alloy composition or structure.
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      Elucidation of the emission red-shift with increasing growth temperature of MBE-grown GaInNAs/GaAs quantum wells
      • Author(s): E.-M. Pavelescu ; M. Dumitrescu ; T. Jouhti ; J. Wagner ; P.J. Klar ; S. Karirinne ; M. Pessa
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 293 –296
      • DOI:  10.1049/ip-opt:20040880
      • Type: Article
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      • p. 293 –296 (4)
        The causes were investigated for the photoluminescence red-shift with increasing quantum well growth temperature (TQW) reported in GaInNAs/GaAs quantum wells grown by molecular-beam epitaxy (Tournié et al., 2002; Chauveau et al., 2003). The phenomenon was found to be due to self-annealing, which occurred during the growth of layers on top of the quantum well at typical substrate temperatures TQW for GaAs growth by molecular-beam epitaxy. This self-annealing induces a blue-shift of the quantum well emission, whose magnitude increases as TQW decreases. The TQW-dependent blue-shift is correlated with the presence of In and occurs without noticeable changes in macroscopic alloy composition or quantum well structure. The underlying cause for the increase in blue-shift with decreasing TQW during self-annealing appears to be an increased number of In–N bonds due to point-defect-assisted diffusion. Possible defects involved are discussed in the paper on a qualitative basis.
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      Temperature and thickness dependences of electron nonradiative transitions in GaInNAs/GaAs SQW investigated by piezoelectric photothermal spectroscopy
      • Author(s): S. Fukushima ; K. Nozoe ; T. Saisyo ; T. Ikari ; M. Kondow
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 297 –300
      • DOI:  10.1049/ip-opt:20040893
      • Type: Article
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      • p. 297 –300 (4)
        Recently, GaInNAs/GaAs single quantum well (SQW) structures have been considered as a new candidate material for an effective infrared LED for optical fibre communications. In order to investigate the electron nonradiative transitions in the GaInNAs SQW layer, piezoelectric photothermal (PPT) spectroscopy was used. The thickness- and the temperature-dependences of the PPT signal for the samples of thickness 10, 5 and 3 nm and from 300 K down to 77 K were investigated. The PPT spectra show a blue shift of the exciton and band-to-band transition with decreasing sample thickness. This was explained by quantum mechanical discussions for the confinement of the charge carriers supposing an electron effective mass of 0.08 m0 and band offset ratio of 6:4. The effect of the induced strain in the quantum well on the electronic structure is also discussed. The decreasing temperature also exhibits a blue shift of the PPT signal peaks and a decrease of the PPT signal amplitude. The temperature variation shows that the nonradiative intraband transition between the heavy and the light hole bands causes the additional contribution to the signal. It is concluded that the present PPT technique is an effective methodology for measuring the electron transitions in the SQW.
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      Improvement in the optical quality of GaInNAs/GaInAs quantum well structures by interfacial strain reduction
      • Author(s): P. Navaretti ; H.Y. Liu ; M. Hopkinson ; M. Gutiérrez ; J.P.R. David ; G. Hill ; M. Herrera ; D. González ; R. García
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 301 –304
      • DOI:  10.1049/ip-opt:20040934
      • Type: Article
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      • p. 301 –304 (4)
        The authors report on the use of thin (2 nm) layers with intermediate strain placed between the barriers and the quantum wells of GaInNAs/GaInNAs structures in order to reduce the effect of strain on the quantum wells. A comparison between samples with and without these strain-mediating layers has been performed using various optical and structural techniques, such as photoluminescence, high-resolution X-ray diffractometry and transmission electron microscopy. The results show that the introduction of strain-mediating layers brings beneficial effects to the structural quality of the active region which, in turn, is reflected by a two orders of magnitude improvement in the photoluminescence intensity. It is thought that this structural design approach can be successfully used to obtain high performance 1.3 and 1.55 μm lasers based on dilute nitride materials grown on GaAs.
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      Effect of nitrogen ions on the properties of InGaAsN quantum wells grown by plasma-assisted molecular beam epitaxy
      • Author(s): J. Miguel-Sánchez ; A. Guzmán ; J.M. Ulloa ; A. Hierro ; E. Muñoz
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 305 –308
      • DOI:  10.1049/ip-opt:20040910
      • Type: Article
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      • p. 305 –308 (4)
        The advantages of the InGaAsN/GaAs system comprising the active layers of single- and multi-quantum well laser diodes (emission wavelengths in the second and third optical windows, AlGaAs reflectors etc.), in comparison with other materials, make this quaternary material an interesting field for study. The monoatomic nitrogen species required for the growth of InGaAsN layers by molecular beam epitaxy, using a radiofrequency power source, are mixed in the plasma with ionised species, among others. The authors present a detailed characterisation of the plasma in the vicinity of the growing surface by measuring its I–V characteristics. A magnetic field was used to deflect ions and their effect on the properties of InGaAsN quantum wells was observed. These ionised species were observed to damage the surface, introducing nonradiative centres. As observed by photoluminescence experiments, the optical quality is improved as the density of ions impinging on the surface is reduced. Rapid thermal annealing experiments were also carried out, showing that the observed PL intensity improvement is related to the ion concentration in the quantum wells.
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      Thermally detected optical absorption and photoluminescence studies of InGaAsN/GaAs quantum wells
      • Author(s): T. Bouragba ; M. Mihailovic ; H. Carrère ; P. Disseix ; A. Vasson ; J. Leymarie ; E. Bedel ; A. Arnoult ; C. Fontaine
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 309 –312
      • DOI:  10.1049/ip-opt:20040929
      • Type: Article
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      • p. 309 –312 (4)
        Both thermally detected optical absorption and photoluminescence as a function of temperature are used to investigate the electronic states of InGaAsN/GaAs quantum wells grown by molecular beam epitaxy. The band structure of InGaAsN is first described within the two-band model, assuming that nitrogen only affects the conduction band through the interaction between the localised nitrogen level and the host matrix conduction band. Taking advantage of the accurate knowledge of strained InGaAs/GaAs layers, a simple model allows the calculation of the energy levels in InGaAsN/GaAs quantum wells. Furthermore, the labelled ten-band k.p model is used to derive the strained conduction band offset. The calculations of transition energies in the wells compare favourably with experimental results. From photoluminescence experiments at different temperatures, the ionisation of impurities together with the transition between localisation–delocalisation of the carriers in the well are evidenced.
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      Photoreflectance and photoluminescence study of step-like GaInNAs/GaInNAs/GaAs quantum wells
      • Author(s): R. Kudrawiec ; M. Motyka ; J. Andrzejewski ; J. Misiewicz ; D. Gollub ; A. Forchel
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 313 –316
      • DOI:  10.1049/ip-opt:20040931
      • Type: Article
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      • p. 313 –316 (4)
        GaInNAs-based quantum well (QW) structures tailored at 1.55 μm are investigated by photoreflectance (PR) and photoluminescence (PL) spectroscopies. The PL intensity and the energy level structure are compared for two types of QWs: GaInNAs/GaAs single QW (SQW) and step-like barrier GaInNAs/GaInNAs/GaAs QW (SLBQW) structures. It is observed that the reduction of N atom concentration in the active QW region from 5.3% (SQW) to 2–2.5% (SLBQWs) leads to the enhancement of PL intensity by a factor of five. Moreover, the introduction of the SLB changes the energy level structure for this system. On the basis of PR measurements, the bandgap energy of the SLB and energies of the transitions in the active QW region were determined. For the structures presented, the SLBs lead to one confined state for electrons and three confined states for heavy holes in the GaInNAs/GaInNAs QW. Transitions related to the three heavy hole sub-bands and the one electron sub-band have been observed in PR spectra.
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      Blue shift in InGaAsN/GaAs quantum wells with different width
      • Author(s): C.S. Peng ; J. Konttinen ; H.F. Liu ; M. Pessa
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 317 –319
      • DOI:  10.1049/ip-opt:20040882
      • Type: Article
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      • p. 317 –319 (3)
        Three InGaAsN/GaAs QWs with well widths of 3, 5 and 9 nm were grown in one single sample with a GaAs barrier width of 35 nm under the same growth conditions. Post-growth rapid thermal annealing (RTA) was applied at 700°C on this sample and photoluminescence (PL) was measured after different RTA times. It was observed that the blue shifts (BS) were the same, up to ∼15 meV in the first 30 s, for all three QWs; after this the BS of the 9-nm QW saturated very soon at 24 meV and the BSs of 5-nm and 3-nm QWs were saturated much more slowly at more than 45 meV and 57 meV, respectively. There are at least two factors that affect the BS: interdiffusion and short-range order (SRO). SRO is started and saturated much faster than interdiffusion during annealing.
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      N2-incorporation-induced blue shift in InGaAsN/GaAs quantum well during annealing
      • Author(s): C.S. Peng ; H.F. Liu ; J. Konttinenn ; M. Pessa
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 320 –322
      • DOI:  10.1049/ip-opt:20040883
      • Type: Article
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      • p. 320 –322 (3)
        Three different kinds of quantum wells (QWs) were grown at the same growth temperature by molecular beam epitaxy (MBE): InGaAs/GaAs QW without any N2 background; InGaAs(N2)/GaAs double QWs with N2 flow to the sample but without plasma; and InGaAsN/GaAs QW with N-plasma. The latter two types of QW were grown on one sample. Post-growth rapid thermal annealing (RTA) was applied to them at 700 °C. After 31.5 min of RTA, it was observed that the photoluminescence blue shift of the InGaAs(N2) QW was 40 meV, which was 9 meV more than that for the InGaAsN QW, and the InGaAs QW had only about 13 meV blue shift. However, for the as-grown case, the PL peak position of the InGaAs QW and InGaAs(N2) QWs were the same (1148 nm), and for the InGaAsN QW it was 220 nm longer. This indicates that there is N2 incorporation during InGaAsN growth, the N2 incorporation does not affect the band structure and the N2 incorporation dominates the blue shift during RTA.
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      Post-growth annealing of GaInNAs layers and GaInNAs/GaAs multiple quantum wells studied by photoreflectance spectroscopy
      • Author(s): R. Kudrawiec ; J. Misiewicz ; E.-M. Pavelescu ; J. Konttinen ; M. Pessa
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 323 –327
      • DOI:  10.1049/ip-opt:20040887
      • Type: Article
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      • p. 323 –327 (5)
        GaInNAs layers almost lattice-matched to a GaAs substrate and GaInNAs/GaAs multiple quantum wells (MQWs) post-growth annealed at different temperatures are investigated by photoreflectance (PR) spectroscopy. The post-growth annealing leads to an ‘effective’ blue-shift of the bandgap energy of GaInNAs layers and GaInNAs/GaAs MQWs without a change in the composition of the GaInNAs layer. This phenomenon is associated with the formation of In–N bonds instead of Ga–N bonds, accompanied by the appearance of N atoms in In-rich environments with larger bandgap energies. It is shown that the annealing-induced blue-shift of the bandgap energy, which is usually observed for GaInAsN structures, is associated with a redistribution of the intensity of the optical features related to the different energy gaps possible for this quaternary material. The findings are a manifestation of the metastability of optical properties for GaInNAs-based structures.
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      Optical properties of GaAsNSe/GaAs superlattice investigated by means of piezoelectric photothermal spectroscopy for nonradiative electron transitions
      • Author(s): K. Sakai ; S. Fukushima ; A. Fukuyama ; K. Uesugi ; I. Suemune ; T. Ikari
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 328 –330
      • DOI:  10.1049/ip-opt:20040869
      • Type: Article
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      • p. 328 –330 (3)
        Optical properties of the GaAsNSe/GaAs superlattice (SL) were investigated using piezoelectric photothermal (PPT) and photoluminescence (PL) spectroscopies. The sample was grown by metalorganic molecular beam epitaxy on a semi-insulating (SI-)GaAs substrate. The SL consists of five periods of GaAsNSe and GaAs layers of thickness 11 nm. The temperature variation of the PPT spectrum of this sample was measured down to liquid nitrogen temperature and three peaks were observed at 0.7, 0.90 and 1.25 eV at 80 K. The 1.25 eV peak seems to be due to the bandgap transition of GaAsNSe. Comparing the PPT spectra with the PL results, it was considered that the localised levels caused the PPT signal peaks at 0.7 and 0.90 eV. The intensity of the 0.90 eV peak drastically changed with secondary light illumination. The effect of the electron nonradiative recombination at the interface states should be considered.
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      Investigations of 1.55-μm GaInNAs/GaAs heterostructures by optical spectroscopy
      • Author(s): H.D. Sun ; A.H. Clark ; S. Calvez ; M.D. Dawson ; H.Y. Liu ; M. Hopkinson ; P. Navaretti ; M. Gutierrez ; J.S. Ng ; J.P.R. David ; P. Gilet ; L. Grenouillet ; A. Million
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 331 –334
      • DOI:  10.1049/ip-opt:20040866
      • Type: Article
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      • p. 331 –334 (4)
        Dilute nitride semiconductors are a topic of major current research interest owing to the novel physics induced by the incorporation of N in small percentages of composition. Related research has been further motivated by the favourable characteristics for device applications of the resultant materials, particularly represented by GaInNAs quaternary compounds as active materials in the 1.3–1.6 μm wavelength range. Whilst 1.3-μm GaInNAs/GaAs materials and devices are now reaching a level of maturity, the extension of these structures to around 1.55 μm is still in its infancy. The authors report optical studies of 1.55-μm GaInNAs/GaAs heterostructures of varying characteristics, all grown by molecular beam epitaxy. As the addition of N complicates the local structure and optical properties in this material system, the PL mechanisms are clarified by detailed PL excitation (PLE) spectra. Whereas all the measured samples exhibit strong PL at room temperature, the electronic structure is quite different between samples grown under different conditions. Some demonstrate clearly standard 2-D quantum well (QW) electronic states and some demonstrate evidence of phase-separated quantum-dot-like (QD) structures.
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      Effects of rapid thermal annealing on optical quality of GaNP alloys
      • Author(s): M. Izadifard ; I.A. Buyanova ; J.P. Bergman ; W.M. Chen ; A. Utsumi ; Y. Furukawa ; A. Wakahara ; H. Yonezu
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 335 –337
      • DOI:  10.1049/ip-opt:20040872
      • Type: Article
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      • p. 335 –337 (3)
        Significant improvements in radiative efficiency of GaNP epilayers grown on GaP substrates by solid-source molecular beam epitaxy (MBE) are achieved by post-growth rapid thermal annealing (RTA). From temperature-dependent CW and time-resolved photoluminescence (PL) spectroscopies combined with PL excitation measurements, the observed improvements are attributed to annealing out of competing nonradiative centres. This conclusion is supported by the following experimental evidence: reduced thermal quenching of the PL intensity resulting in a substantial (up to 18 times) increase at room temperature (RT) after RTA, and simultaneous improvements in carrier lifetime at RT deduced from time-resolved PL measurements.
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      Percolation-based multimode Ga–N behaviour in the Raman spectra of GaInAsN
      • Author(s): T. Tite ; A. Chafi ; J.P. Laurenti ; O. Pagès ; D. Bormann ; E. Tournié
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 338 –341
      • DOI:  10.1049/ip-opt:20040928
      • Type: Article
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      • p. 338 –341 (4)
        The transverse optical (TO) and longitudinal optical (LO) phonons of bulk (∼1-μm-thick) as-grown Ga1−yInyAs1−xNx/GaAs (001) layers with x∼0.03–0.04 and y up to 0.30 are investigated by Raman scattering. Three-mode behaviour is observed which discriminates between Ga–N modes from isolated N atoms (∼460 cm−1), clustered N in a Ga environment (∼425 cm−1) and N involved in Ga3InN complexes (∼480 cm−1). The local N-bonding in GaInAsN is quantitatively estimated via full contour modelling of the TO multimode Ga–N Raman lineshapes. In particular, it is found that the incorporation of In can significantly reduce GaN segregation, but only for a very narrow range of N compositions just above the theoretical N-solubility limit xs∼0.02 in GaAs.
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      Comparative optical study of GaAs1−xNx/GaAs and BxGa1−xAs/GaAs epilayers
      • Author(s): F. Saidi ; F. Hassen ; H. Maaref ; H. Dumont ; Y. Monteil
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 342 –345
      • DOI:  10.1049/ip-opt:20040938
      • Type: Article
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      • p. 342 –345 (4)
        Optical studies of GaAs1−xNx/GaAs and BxGa1−xAs/GaAs epilayers grown by metal organic chemical vapour deposition (MOCVD), with various nitrogen (N) and boron (B) compositions, have been achieved by photoluminescence spectroscopy (PL) as a function of the excitation density and the sample temperature (10–300 K). The experiments have shown that the GaAsN PL band emission presents a more significant red shift than the BGaAs emission. For the GaAsN a reduction of 110 meV/1%N is shown, but for the BGaAs the PL band emission shifts to the low-energy side by up to 2.5%. A more significant blue shift of the PL bands with increasing the excitation density has been observed for GaAsN compared to BGaAs epilayer structures. The temperature dependence of the PL peak energy has shown S-shaped behaviour for both structures, but the localisation effects are more important in GaAsN than in BGaAs. Based on these experimental results, it is shown that B incorporation does not cause large modification of the band structure in BxGa1−xAs alloys compared to pure GaAsN structures.
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      Exciton localisation in InGaAsN and GaAsSbN observed by near-field magnetoluminescence and scanning optical microscopy (NSOM)
      • Author(s): J.L. Merz ; A.M. Mintairov ; T. Kosel ; K. Sun
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 346 –351
      • DOI:  10.1049/ip-opt:20040881
      • Type: Article
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      • p. 346 –351 (6)
        The authors present measurements of photoluminescence spectra and imaging of the sharp emission lines which result from the radiative recombination of excitons trapped in compositional fluctuations in dilute nitride epitaxial layers and quantum wells, using low-temperature near-field scanning optical microscopy (NSOM). Both weak and strong localisation (i.e. quantum-dot-like emission) are observed for samples of GaAsN and InGaAsN, with little difference depending on the presence or absence of In. Localisation energies are in the range 10–60 meV. Zeeman splitting and diamagnetic shifts are observed in the near-field magneto-photoluminescence, and from these effects the size (r=3–17 nm), composition fluctuations (Δy ∼0.5%) and density (100–1000 μm−3) of the compositional clusters are determined. Using two-dimensional NSOM images, the authors observe a strong lateral inhomogeniety for the GaAsN epilayers resulting from nitrogen clustering. A one-dimensional compositional modulation along the [110] direction is also observed for a GaAsSbN quantum well on the length scale of 100 nm. Transmission electron micrographs confirm the existence of these spatial nonuniformities. Time-resolved spectroscopy has also been carried out on one of the samples reported here (In0.08GaAsN0.03). Pump-and-probe photoluminescence experiments provide the following time constants: the exciton relaxation time to the ground states of the localisation regions is found to be ∼40–70 ps as the emission varies from high to low energy, and the time for depopulation of these localised states is 2–4 ns.
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      Intrinsic limits on electron mobility in disordered dilute nitride semiconductor alloys
      • Author(s): S. Fahy ; A. Lindsay ; E.P. O'Reilly
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 352 –356
      • DOI:  10.1049/ip-opt:20040876
      • Type: Article
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      • p. 352 –356 (5)
        The authors have previously shown that there is a fundamental connection between the composition-dependence of the conduction-band-edge energy and the n-type carrier scattering cross-section in dilute alloys, imposing general limits on the electron mobility in Ga(In)NAs alloys and heterostructures. A simple general expression is derived for scattering in the ultra-dilute regime, showing that the scattering rate is proportional to |dEc/dx|2, the square of the initial variation of the conduction-band-edge energy with alloy composition x. The mobility estimated in GaNxAs1−x using the two-level band-anti-crossing (BAC) model is of the right magnitude (∼1000 cm2/Vs), but still larger than typical experimental values. The effects of N clusters and inhomogeneous broadening of energy levels are considered, including the formation of N–N pairs (where a single Ga atom has two N neighbours) and more complex clusters. It is shown that such complexes play a major role in further limiting the mobility, giving values of 200–400 cm2/Vs, in close agreement with experiment. It is concluded that random alloy scattering, rather than film quality or other factors, dominates the carrier mobility in these materials.
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      Influence of N on the electron transport in (Ga, In)(N, As) probed by magnetotransport under hydrostatic pressure
      • Author(s): J. Teubert ; P.J. Klar ; W. Heimbrodt ; K. Volz ; W. Stolz
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 357 –360
      • DOI:  10.1049/ip-opt:20040892
      • Type: Article
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      • p. 357 –360 (4)
        Incorporation of small amounts of nitrogen into GaAs and (Ga, In)As results in considerable changes of the electronic properties of these materials. Whereas the optical properties have already been extensively studied, there is little knowledge about the effects of nitrogen incorporation on the electronic transport behaviour of these III–V alloys. Magnetoresistance (MR) and Hall measurements at temperatures of 2–280 K and fields up to 10 T show large negative MR effects for n-type samples, whereas p-type samples behave like conventional III–V alloys. Results of magnetotransport measurements under hydrostatic pressure up to 20 kbar for n-type (Ga, In)(N, As) samples are presented. All the results can be explained qualitatively by the energetic and spatial disorder effects induced by N in the conduction band.
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      Ultrafast carrier dynamics in nitrogen-implanted GaAs
      • Author(s): S. Sinning ; T. Dekorsy ; M. Helm
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 361 –364
      • DOI:  10.1049/ip-opt:20040871
      • Type: Article
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      • p. 361 –364 (4)
        The comparative analysis of the ultrafast carrier dynamics of pure GaAs and ion-implanted GaNAs is reported. Different nitrogen concentrations (up to 4%) are implanted and subsequently annealed by rapid thermal annealing (RTA). Damage analysis by channelling Rutherford backscattering (RBS) reveals that the annealing step improves the crystal quality, but does not restore the original quality. From photoreflectance measurements it is concluded that the highest achieved active nitrogen content in the implanted samples is 0.5% for an equivalent implantation dose of 1%. Carrier dynamics are investigated by one-colour pump-probe measurements covering an excitation wavelength range of 730–860 nm (1.7–1.44 eV) with femtosecond time resolution. Comparison with non-implanted GaAs indicates that the carrier relaxation in the implanted samples is dominated by traps associated with implantation damage.
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      Carrier recombination processes in GaAsN: from the dilute limit to alloying
      • Author(s): R. Intartaglia ; T. Taliercio ; P. Lefebvre ; P. Valvin ; T. Bretagnon ; T. Guillet ; B. Gil ; U. Tisch ; E. Finkman ; J. Salzman ; M.-A. Pinault ; E. Tournié
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 365 –368
      • DOI:  10.1049/ip-opt:20040867
      • Type: Article
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      • p. 365 –368 (4)
        Low-temperature time-resolved photoluminescence (TR–PL) experiments were used to study the dependence on nitrogen composition of the nature, the energy and the dynamics of radiative carrier recombinations in GaAs1−xNx alloys. Epitaxial layers were grown on (001) GaAs substrates by molecular beam epitaxy using solid sources for group-III and As elements, and a radiofrequency plasma source for N. The nitrogen content, measured by secondary ion mass spectroscopy, was in the range 5 × 10-5 – 7 × 10-2. PL spectra are dominated by the emission from the discrete states of nitrogen-based excitonic complexes for the very low x regime (around 5 × 10-5), showing exponential time decays. For x larger than 5 × 10-4, PL spectra are rather dominated by emission from a continuum of states originating from nitrogen clusters. In this case, nonexponential time decays are obtained. It is shown that these PL decays involve complex carrier transfers between the various available states. Changing the nitrogen content changes the recombination mechanism by changing the distance between the clusters.
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      Physics of defects and hydrogen in dilute nitrides
      • Author(s): S.B. Zhang ; A. Janotti ; S.-H. Wei ; C.G. Van de Walle
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 369 –377
      • DOI:  10.1049/ip-opt:20041037
      • Type: Article
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      • p. 369 –377 (9)
        First-principles theory is capable of unveiling physical properties of the various defects in dilute nitrides. The authors discuss some of their recent results for native defects, N–N pairs, as well as for hydrogen in GaAsN and GaPN. The studies have shown that defect physics of dilute nitrides is qualitatively different from that of conventional semiconductors owing to the involvement of nitrogen. This leads to a number of phenomena ranging from the existence of a new class of intrinsic traps, such as the N–N split interstitials, AsGa–N and VGa–N pairs, to a surprising modification of the fundamental bandgap by hydrogen.
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      Defects in dilute nitrides: significance and experimental signatures
      • Author(s): W.M. Chen ; I.A. Buyanova ; C.W. Tu
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 379 –384
      • DOI:  10.1049/ip-opt:20040939
      • Type: Article
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      • p. 379 –384 (6)
        A brief review of experimental results of defects in dilute nitrides studied by various techniques reported so far in the literature is given. The emphasis is on experimental signatures of grown-in defects in Ga(In)NAs and Ga(Al)NP, which are expected to play important roles in device performance and in determining the success of this novel material system for applications in optoelectronics. The authors' recent results from optically detected magnetic resonance studies of grown-in intrinsic defects, i.e. AsGa antisite in Ga(In)NAs and Ga self-interstitials in Ga(Al,In)NP, are discussed in more detail, in an effort to provide detailed information on the chemical identification and the formation mechanism of the defects as well as to reveal their role in degrading the optical quality of the materials. The review aims not only to provide an overview of the present knowledge and understanding of defects in dilute nitrides, but also to stress the urgent need for concerted efforts to positively identify the most important defects that are harmful to device performance and to design strategies to suppress them during growth or to eliminate them by post-growth treatments.
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      Structural defects characterisation of GaInNAs MQWs by TEM and PL
      • Author(s): M. Herrera ; D. González ; R. García ; M. Hopkinson ; P. Navaretti ; M. Gutiérrez ; H.Y. Liu
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 385 –388
      • DOI:  10.1049/ip-opt:20040870
      • Type: Article
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      • p. 385 –388 (4)
        The authors' work is focused on the structural and optical properties of GaInNAs/GaAs(001) QWs with In and N contents in the ranges 0.20–0.35 and 0.013–0.023, respectively, studied by transmission electron microscopy and photoluminescence. An undulation of the wells was observed when increasing the In content to 25% and the N content to 1.6%. This induces the appearance of extrinsic Frank dislocation loops, which are most likely formed because of local stress accumulation in the structure. The PL spectra show intense peaks at 1.1 μm and 1.2 μm for samples with In compositions of 20% and 25%, respectively, representing therefore structures with and without loops. Consequently, the existence of these structural defects seems not to affect the optical efficiency of this alloy. On increasing the In content to 35%, a considerable decrease in the PL peak intensity, related to the existence of threading dislocations observed by TEM, has been found. The unfaulting of dislocation loops by means of the reaction with two Shockley partial dislocations is proposed as the mechanism of formation of these threading dislocations.
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      Origin of bandgap bowing in GaNP alloys
      • Author(s): I.A. Buyanova ; M. Izadifard ; W.M. Chen ; H.P. Xin ; C.W. Tu
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 389 –392
      • DOI:  10.1049/ip-opt:20040865
      • Type: Article
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      • p. 389 –392 (4)
        By employing photoluminescence excitation (PLE) spectroscopy, the authors provide direct evidence for N-induced strong coupling and repelling of host conduction band (CB) states in GaNxP1−x. This strong coupling is manifested as (i) a drastic change in the ratio of oscillator strengths between the optical transition near Eg\rGamma and that near the CB minimum (CBM); (ii) a strong blue shift of the a1(Γ) state with increasing N composition accompanying a red shift of the CBM; (iii) pinning of the energies of the N-related levels; and (iv) the appearance of t2(L) or t2(X3) upon N incorporation of which the energy position is insensitive to N compositions. These findings shed new light on the controversial issue of the dominant mechanism responsible for the giant bandgap bowing of dilute nitrides.
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      Boundary conditions for the electron wavefunction in GaInNAs-based quantum wells and modelling of the temperature-dependent effective bandgap
      • Author(s): M. Hetterich ; A. Grau ; A.Yu. Egorov ; H. Riechert
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 393 –396
      • DOI:  10.1049/ip-opt:20040874
      • Type: Article
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      • p. 393 –396 (4)
        The boundary conditions were investigated for the electron wavefunction in Ga1−xInxNyAs1−y-based heterostructures described by the band anticrossing model. Among other advantages, the utilisation of these boundary conditions simplifies the calculation of, for example, transition energies in quantum wells. The derived equations were applied to model the temperature-dependence of the effective bandgap in Ga1−xInxNyAs1−y/GaAs quantum well structures with high indium concentration. From a fit to the experimental photoreflectance data, evidence was found to show that the nitrogen level EN in the band anticrossing Hamiltonian, measured with respect to the valence band edge, shifts to higher energies with decreasing temperature. This extends similar results reported in the literature for low indium content epilayers.
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      Influence of cluster states on band dispersion in bulk and quantum well (ultra-)dilute nitride semiconductors
      • Author(s): S.B. Healy ; A. Lindsay ; E.P. O'Reilly
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 397 –401
      • DOI:  10.1049/ip-opt:20040875
      • Type: Article
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      • p. 397 –401 (5)
        The band-anti-crossing (BAC) model successfully describes many of the electronic properties of GaNxAs1−x. Experimental and theoretical studies show a range of resonant defect levels close to the conduction band edge in GaNxAs1−x, due to the formation of N complexes which are ignored in the conventional BAC model. The consequences of these resonant levels for the band dispersion are investigated. The rapid increase in N–N pairs with N composition (∝x2) is shown to have little effect on the calculated room-temperature band-edge dispersion, but modifies the low-temperature band dispersion with increasing x. For low temperatures, it is shown that at low N composition (0.001≤x≤0.01) the band dispersion is best described using a modified BAC model, which explicitly includes the effects of N–N pairs, while at higher compositions (x>0.01) the effects of longer-range N–N interactions need also to be considered. The consequences of this are analysed for the predicted evolution of band dispersion with x in magneto-tunnelling experiments.
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      Band structure calculation of InGaAsN//GaAs, InGaAsN//GaAsP//GaAs and InGaAsN//InGaAsP//InP strained quantum wells
      • Author(s): H. Carrère ; X. Marie ; J. Barrau ; T. Amand ; S. Ben Bouzid ; V. Sallet ; J.-C. Harmand
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 402 –406
      • DOI:  10.1049/ip-opt:20040909
      • Type: Article
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      • p. 402 –406 (5)
        The authors have calculated the band structure of 1.3-μm InGaAsN/GaAs(N)/GaAs compressively strained quantum wells (QW) using the band anticrossing model and an eight-band k.p Hamiltonian. The calculated interband optical transition energies have been compared to the experimental ones deduced from photocurrent. Because of the high compressive strain in the QW, strain-compensated structures may be required in order to grow stable multiple QWs; with this in view, the band structure of InGaAsN/GaAsP/GaAs QWs emitting at 1.3 μm was studied. Dilute nitride structures also offer the possibility of growing tensile-strained QW lasers emitting at 1.55 μm on an InP substrate. In order to evaluate the potentialities of such structures, the band characteristics of InGaAsN/InGaAsP/InP heterostructures were determined with a TM-polarised fundamental transition around 1.55 μm.
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      GaInNAs(Sb) long wavelength communications lasers
      • Author(s): J.S. Harris ; S.R. Bank ; M.A. Wistey ; H.B. Yuen
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 407 –416
      • DOI:  10.1049/ip-opt:20040937
      • Type: Article
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      • p. 407 –416 (10)
        Dilute nitride GaInNAs and GaInNAsSb alloys grown on GaAs have quickly become excellent candidates for a variety of lower cost 1.2–1.6 μm lasers, optical amplifiers and high-power Raman pump lasers that will be required to power the Internet and advanced communications systems capable of delivering multi-Gbit/s data rates to the desktop. Two particularly critical devices are vertical-cavity surface-emitting lasers (VCSELs) which must operate at high data rates (≥10 Gbit/s), uncooled over a broad thermal operating range and high power (≥500 mW) edge-emitting lasers for Raman amplifier pumps. Despite the fact that these materials are grown in a metastable regime, and there are still many remaining challenges, progress has been both rapid and very promising. Some of the material challenges include the limited solubility of N in GaAs, nonradiative defects that are caused by either or a combination of N incorporation, low growth temperature, and ion damage from the N plasma source. N and Sb add a unique set of properties to this metastable alloy; however, this significantly increases the complexity of its characterisation. The addition of Sb significantly improves the epitaxial growth and optical properties of the material at wavelengths longer than 1.3 μm and broadens the range of In and N composition alloys that can be grown. By adding Sb to the alloy, luminescence has been greatly enhanced between 1.3 and 1.6 μm where normally poor quality material results. Progress in overcoming some of the material challenges is described, particularly GaAsNSb against GaNAs QW barriers, plasma-source ion damage and progress in realising record-setting edge-emitting lasers and the first VCSELs operating at 1.5 μm based on GaInNAsSb QWs grown by solid-source MBE on GaAs.
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      Optimisation of GaAs-based (GaIn)(NAs)//GaAs vertical-cavity surface-emitting diode lasers for high-temperature operation in 1.3-μm optical-fibre communication systems
      • Author(s): R.P. Sarzała  and  W. Nakwaski
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 417 –420
      • DOI:  10.1049/ip-opt:20040936
      • Type: Article
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      • p. 417 –420 (4)
        Performance of GaAs-based (GaIn)(NAs)/GaAs vertical-cavity surface-emitting diode lasers (VCSELs) at higher temperatures for second-generation optical-fibre communication systems is examined with the aid of the comprehensive threshold fully self-consistent optical-electrical-thermal-gain model. As expected, in standard double-oxide-confined VCSELs, an increase in the active-region diameter is followed by an increase in the lowest-threshold transverse mode order, especially at higher temperatures. It has been found that reduction of a diameter of the bottom aperture may ensure fundamental LP01 mode operation even at higher temperatures.
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      Optoelectronic properties of 2-D and 3-D-grown GaInNAs//GaAs QW light emitting diodes and laser diodes
      • Author(s): J.-M. Ulloa ; A. Hierro ; J. Miguel-Sanchez ; A. Guzman ; A. Trampert ; J.L. Sanchez-Rojas ; E. Calleja
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 421 –425
      • DOI:  10.1049/ip-opt:20040911
      • Type: Article
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      • p. 421 –425 (5)
        The optoelectronic properties of light emitting diodes (LEDs) and laser diodes (LDs) based on GaInNAs/GaAs quantum wells (QWs) grown under two-dimensional (2-D) and three-dimensional (3-D) conditions are compared. In spite of the longer wavelength, the 2-D LED shows better luminescence properties than the one with island formation. The broadening of the photocurrent spectra and the Stokes shift are used to analyse carrier localisation effects. The emission from localised states is found to impact the electroluminescence of the 3-D device even at room temperature, while it does not significantly influence the high-temperature emission of the 2-D LED. From a detailed analysis of the low-temperature electroluminescence as a function of injected current, nonradiative recombination is found to be the main carrier recombination mechanism in a wide range of currents in the 3-D LED, while it is very small in the 2-D case. Consequently, defect formation seems to be closely related to the 3-D growth, limiting laser emission in these structures. These results suggest that 2-D-grown GaInNAs/GaAs QWs may be more desirable for achieving laser emission at long wavelengths.
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      Low threshold, high power and long lifetime InGaAsN/GaAs lasers
      • Author(s): C.S. Peng ; N. Laine ; J. Konttinen ; T. Jouhti ; M. Pessa
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 426 –428
      • DOI:  10.1049/ip-opt:20040884
      • Type: Article
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      • p. 426 –428 (3)
        4 μm stripe ridge waveguide InGaAsN lasers were processed. Pulsed (10 μs, 1% duty) emission was up to 240 mW at 20 °C and 20 mW at 120 °C. The emission wavelength is around 1260 nm at RT. The threshold is 15 mA at 20 °C, corresponding to a threshold current density of 313 A/cm2. For CW operation, the lasers show a very low threshold of 23 mA and the maximum output was up to 40 mW for a 1200 μm length chip at RT. All the emission described was kink-free and single-mode. The laser with broad area (40 μm stripe width) processing using the same material has been working under CW operation at constant current (80% of maximum output) for more than 15 500 device-hours at 30 °C and is still working well.
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      High-frequency performance of triple quantum well GaInNAs/GaAs ridge waveguide lasers emitting at 1.35 μm
      • Author(s): A. Martinez ; V. Sallet ; D. Jahan ; J.-G. Provost ; J. Landreau ; O. Le Gouezigou ; B. Dagens ; L. Ferlazzo ; J.-C. Harmand ; A. Ramdane
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 429 –432
      • DOI:  10.1049/ip-opt:20040878
      • Type: Article
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      • p. 429 –432 (4)
        Static performances and high-frequency characterisation of a GaInNAs/GaAs laser diode emitting at 1.35 μm are reported. Optimised molecular beam epitaxial (MBE) growth has allowed the achievement of a triple quantum well stack for improved dynamic properties. Broad area lasers exhibit a transparency current density of 642 A/cm2 at 20°C under pulsed operation and a characteristic temperature T0 of 80 K. Single-mode narrow-ridge waveguide devices emitting at 1.34 μm demonstrate a low threshold current of 26 mA under continuous wave (CW) operation at 25°C for an HR/as-cleaved cavity. The maximum output power reaches 9 mW with a slope efficiency of 0.13 W/A under CW operation. Intrinsic dynamic properties of the devices have been evaluated through relative intensity noise (RIN) measurements and small signal modulation. The dependence of the relaxation frequency on the bias current shows a slope of 0.92 GHz/mA1/2. The evolution of the damping factor against the squared relaxation frequency gives a K factor of 0.44 ns. RIN measurements yield a record relaxation frequency of 7.4 GHz for this triple-QW device. Small signal modulation shows a 3 dB bandwidth of 9.7 GHz for this new material system, compatible with 10-Gbit/s applications.
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      (Ga,In)(N,As)-based solar cells grown by molecular beam epitaxy
      • Author(s): B. Damilano ; J. Barjon ; S.W. Wan ; J.-Y. Duboz ; M. Leroux ; M. Laügt ; J. Massies
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 433 –436
      • DOI:  10.1049/ip-opt:20040890
      • Type: Article
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      • p. 433 –436 (4)
        (Ga,In)(N,As) could be a promising material for use in monolithic four-junction solar cells since it can be grown lattice-matched to substrates such as GaAs and Ge, and its bandgap of 1 eV is complementary to that of the three other semiconductors Ge, GaAs and (Ga,In)P. The growth by molecular beam epitaxy of (Ga,In)(N,As)-based solar cells is reported. It was checked by high-resolution X-ray diffraction that the 1-μm-thick (Ga,In)(N,As) layers were lattice-matched to GaAs. The spectral responses of the solar cells provide evidence that (Ga,In)(N,As) converts photons with energy down to 0.9 eV. The comparison with reference GaAs solar cells indicates, however, a degradation of the short-circuit current, revealing short minority-carrier diffusion lengths. A (Ga,In)(N,As) 2 mm×2.5 mm solar cell with a p–i (Ga,In)(N,As) n-GaAs structure delivers a 2.1 mA/cm2 short-circuit current and has an open-circuit voltage of 0.264 V under natural solar illumination (air mass ∼1.5).
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      GaInNAs SESAMs passively mode-locking 1.3-μm solid-state lasers
      • Author(s): V. Liverini ; S. Schön ; R. Grange ; M. Haiml ; S.C. Zeller ; U. Keller
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 437 –441
      • DOI:  10.1049/ip-opt:20040877
      • Type: Article
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      • p. 437 –441 (5)
        A GaInNAs semiconductor saturable absorber mirror (SESAM) is demonstrated that is able to passively mode-lock a 1.3-μm Nd:YLF laser. The mirror was grown by molecular beam epitaxy and consists mainly of a GaInNAs single quantum well on an AlAs/GaAs distributed Bragg reflector. Two designs were grown: resonant and antiresonant. The first favoured optical characterisation, while the second one was more fitted to self-start passive mode-locking in the laser. Rapid thermal annealing was used to tune this wavelength closer to the desired laser wavelength of 1314 nm. Nonlinear characterisation of both designs allowed calculation of the saturation fluence of a 10-nm GaInNAs QW with photoluminescence around 1330 nm independently of design. It was measured to be 3.5±0.5 μJ/cm2. The incorporation of about 2% of N in In0.36Ga0.64As red-shifted the as-grown photoluminescence to about 1370 nm. The nonlinear optical characterisation of the antiresonant SESAM showed low saturation fluence (11.2 μJ/cm2), low nonsaturable losses and a recovery time suitable for ps-pulse generation. With this SESAM we obtained clean self-starting mode-locking with 6.7-ps pulses at a repetition rate of 117 MHz and a maximum average output power of 580 mW.
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      1.3-μm GaInNAs surface-normal devices
      • Author(s): S. Calvez ; N. Laurand ; S.A. Smith ; A.H. Clark ; J.-M. Hopkins ; H.D. Sun ; M.D. Dawson ; T. Jouhti ; J. Kontinnen ; M. Pessa
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 442 –446
      • DOI:  10.1049/ip-opt:20040868
      • Type: Article
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      • p. 442 –446 (5)
        The compatibility of GaInNAs/GaAs active regions with AlGaAs Bragg mirror technology opens up a range of surface-normal device formats for the spectral region around 1.3 μm. The authors report recent progress on the development of diode-pumped vertical external-cavity surface emitting lasers (VECSELs) and vertical cavity semiconductor optical amplifiers (VCSOAs) based on this technology. Pertinent performance characteristics are reported for GaInNAs 1.3-μm VECSELs capillary-bonded to diamond heatspreader platelets. In a conventional three-mirror air-spaced laser cavity up to 0.6 W of TEM00 output power was obtained. With the outer surface of the diamond platelet coated to form a dielectric output coupler mirror, it was possible to obtain the first monolithic microchip operation of a GaInNAs VECSEL, where a Gaussian beam with output power up to 120 mW was obtained. The influence of temperature on the performance of a six-quantum-well VCSOA with on-chip gain values of up to 16 dB was also reported. It reveals that on-chip gain of 9 dB can be achieved over a range of 85°C, allowing the amplifier characteristics to be tuned over more than 9.5 nm. Further investigations of the influence of optical feedback on the performance of these vertical amplifiers demonstrate that a three-mirror analysis explains the observed phenomena.
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      Influence of growth temperature on carrier recombination in GaInNAs-based lasers
      • Author(s): R. Fehse ; S.J. Sweeney ; A.R. Adams ; D. McConville ; H. Riechert ; L. Geelhaar
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 447 –451
      • DOI:  10.1049/ip-opt:20040886
      • Type: Article
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      • p. 447 –451 (5)
        Relatively small changes in growth parameters, such as the active layer growth temperature, have been shown to have dramatic effects on the threshold current density Jth for GaInNAs-based lasers. The authors consider the influence of the growth temperature on the contribution of the defect-related current to Jth in structures with nominally identical quantum wells. The two sets of devices used in this study are 1.27-μm GaInNAs SQW edge-emitting lasers which are nominally identical except that the active regions were grown at 422°C and 456°C. At room temperature it was found that Jth for the high growth temperature lasers (∼330 A/cm2) is reduced by a factor of ∼2.8 when compared to Jth of the low growth temperature devices (∼970 A/cm2). To determine the processes responsible for this change the light emitted from a window in the substrate contact of the devices was measured as a function of current and temperature, which yields the absolute magnitudes of the defect-, radiative- and Auger-related recombination processes at threshold. The results show that the strong increase in Jth with changing growth conditions can be explained almost entirely by an increase in the monomolecular recombination coefficient A, yielding a larger defect-related current contribution. Furthermore, the extracted radiative- and Auger-related current paths in the two devices are of very similar magnitude. This is strong evidence that the change in growth conditions does not affect the internal losses of the devices, as the threshold carrier density nth appears not to have changed significantly. By increasing the number of wells to three, Jth per well of the high growth temperature devices could be further reduced (∼190 A/cm2) at room temperature. The results suggest that increasing the number of wells not only decreases the carrier density at threshold but additionally reduces the average defect-related current density in these devices.
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      Synthesis and properties of highly mismatched II–O–VI alloys
      • Author(s): K.M. Yu ; W. Walukiewicz ; M.A. Scarpulla ; O.D. Dubon ; W. Shan ; J. Wu ; J.W. Beeman ; P. Becla
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 452 –459
      • DOI:  10.1049/ip-opt:20040932
      • Type: Article
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      • p. 452 –459 (8)
        Ternary and quaternary dilute II–VI oxides were synthesised using a highly non-equilibrium method: the combination of O ion implantation and pulsed-laser melting. CdOxTe1−x thin films have been produced with x up to 0.015 and with the energy gap reduced by 0.15 eV. Optical transitions corresponding to both the lower (E−) and upper (E+) conduction sub-bands, resulting from the anticrossing interaction between the localised O states and the extended conduction states of the matrix, are clearly observed in quaternary Cd0.6Mn0.4OxTe1−x and Zn0.88Mn0.12OxTe1−x layers. These results have important implications for the existing theoretical models of the electronic structure of the highly mismatched alloys. In Zn1−xMnxTe, where the O level lies below the conduction band edge, it was demonstrated that incorporation of a small amount of oxygen leads to the formation of a narrow, oxygen-derived band of extended states located well below the conduction band edge of the ZnMnTe matrix. The three absorption edges of this material (∼0.73, 1.83 and 2.56 eV) cover the entire solar spectrum providing a material envisioned for multiband, single-junction, high-efficiency photovoltaic devices.
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      Mutual passivation effects in highly mismatched group III–V–N alloys
      • Author(s): J. Wu ; K.M. Yu ; W. Walukiewicz
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 460 –464
      • DOI:  10.1049/ip-opt:20040933
      • Type: Article
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      • p. 460 –464 (5)
        The authors have recently discovered a new effect in the dilute InGaAsN alloy system in which electrically active substitutional Si donors and isoelectronic N atoms passivate each other's activity. This is manifested in a drastic reduction of the free electron concentration and, simultaneously, an increase in the fundamental bandgap in Si-doped InGaAsN alloys. Systematic studies of the mutual passivation effect in Si-doped InGaAsN alloys show that the passivation process is controlled by the diffusion of Si to the nearest neighbours of N-occupied sites, forming nearest neighbour Si–N pairs. Analytical calculations of the passivation process based on Ga-vacancy-mediated diffusion show good agreement with the experimental results. It is shown that the mutual passivation provides a method to precisely control electrical properties of InGaAsN:Si. Investigations were made of scattering mechanisms limiting electron mobility in InGaAsN through a judicious choice of the annealing conditions to vary the electron concentration by more than two orders of magnitude. The mobility of free electrons in InGaAsN is quantitatively explained on the basis of the band anticrossing model.
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      Effect of lattice ionicity on hydrogen activity in II–VI materials containing isoelectronic oxygen impurities
      • Author(s): M. Felici ; V. Cesari ; A. Polimeni ; A. Frova ; M. Capizzi ; Y.D. Choi ; B. O ; Y.-M. Yu ; Y. Nabetani ; Y. Ito ; T. Okuno ; T. Kato ; T. Matsumoto ; T. Hirai ; I.K. Sou ; W.K. Ge
      • Source: IEE Proceedings - Optoelectronics, Volume 151, Issue 5, p. 465 –468
      • DOI:  10.1049/ip-opt:20040912
      • Type: Article
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      • p. 465 –468 (4)
        The authors studied the effect of hydrogen irradiation on the optical properties of ZnTe, ZnTe1−ySy (y=0.015) and ZnSe1−xOx (x=0.0023, 0.0057 and 0.009) epilayers. Photoluminescence measurements show the full passivation of O-related recombination bands in ZnTe and ZnTe0.985S0.015 samples unintentionally doped with oxygen. However, hydrogen irradiation does not affect the bandgap reduction following O incorporation in ZnSe1−xOx alloys. This lack of interaction between O and H in ZnSe1−xOx points toward a scarce localised character in the ZnSe1−xOx band edges, as supported by the study of the temperature dependence of the ZnSe1−xOx bandgap.
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