This chapter deals with the use of ion beam analysis (IBA) techniques, in particular in channeling geometry, to study defects in semiconductors. After a tutorial (Section 11.1) introducing the basic principles of IBA and channeling techniques, selected examples of their use to characterize defects (e.g., lattice location of dopants and implantation damage) are described in Section 11.2. Finally, Section 11.3 consists of a brief outlook into future developments and applications.

The impact of substrate doping on the short-channel effects (SCEs) of bulk-planar junctionless transistor (BPJLT) has been studied. It has been found that increasing substrate doping in bulk region reduces off-state leakage current (I _OFF) and the sub-threshold slope (SS) of the device. To further reduce the SCEs of BPJLT heavily doped δ-layer of thickness 10 nm has been added below the channel. Despite the presence of δ-layer in BPJLT reduces SCEs, the SCE, mainly SS, is still limited by the fundamental limit of 60 mV/decade. Therefore, to reduce SS below 60 mV/decade, negative capacitance (NC) δ-BPJLT has been proposed by adding the layer of ferroelectric material at gate stack. It has been found that in comparison with conventional BPJLT and δ-BPJLT, the insertion of ferroelectric layer in NC-δ-BPJLT not only reduces the I _OFF and the SS but also improves I _ON/I _OFF ratio of the device. Thus, embedding heavily doped δ-layer in the bulk region and the ferroelectric layer at the gate stack of BPJLT makes it a promising device for low-power applications.

Hexagonal CdS and Fe-doped CdS nanorods were synthesised by a facile hydrothermal method and characterised by X-ray diffraction, energy dispersive X-ray spectroscopy, UV–vis absorption, photoluminescence, and X-ray photoelectron spectroscopy. The magnetic properties of undoped and Fe-doped CdS nanorods were investigated at room temperature. The experimental results demonstrate that the ferromagnetism of the Fe-doped CdS nanorods differs from that of the undoped CdS nanorods. The remanence magnetisation (M _r) and the coercive field (H _c) of the Fe-doped CdS nanorods were 4.9 × 10⁻³ emu/g and 270.6 Oe, respectively, while photoluminescence properties were not influenced by doping. First-principle calculations show that the ferromagnetism in Fe-doped CdS nanocrystal arose not only from the Fe dopants but also from the Cd vacancies, although the main contribution was due to the Fe dopants.

A simple and new solid-state molten-salt method to synthesise silver (Ag)-doped titanium dioxide (TiO₂) nanoparticles for solar light-induced photocatalytic applications is examined. Ag-doped TiO₂ nanoparticles with varied Ag content ranging from 3 to 10% were synthesised by a single-step molten-salt synthesis method. The effect of Ag content on the antibacterial and photocatalytic activity of nanoparticles was tested. The prepared nanoparticles were studied by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectrometry, ultraviolet–visible (UV–vis) diffusive reflectance spectrometer (UV–vis DRS) and powder X-ray diffraction. The SEM image of nanoparticles clearly showed the presence of agglomerated spherical particles. The EDX analysis of the particles confirmed successful doping of particles in the presence of the Ag in the particles. The doping of Ag in TiO₂ produced TiO₂ pure anatase phase. According to UV–vis DRS results, increasing Ag-doped content in the Ag-doped TiO₂ resulted in a higher visible absorption capability of the materials. Ag doping also improved the antibacterial and photocatalytic activity of TiO₂ nanoparticles. The maximum photocatalytic activity under light irradiation was observed for 5% Ag-doped TiO₂.

The low Pr-doped Bi₂O₃ photocatalyst was prepared via the acrylamide polymerisation method. The photocatalytic activity of prepared samples was evaluated by degrading methyl orange under visible-light irradiation. In comparison to α-Bi₂O₃ nanoparticles, 4% Pr-α-Bi₂O₃ photocatalyst exhibit obviously enhanced photocatalytic performance. The theoretical calculation and experimental results show that Pr doping can extend the optical absorption range from 436 to 518 nm and improve the photocatalytic efficiency from 40.9 to 70.4%. This long-wavelength response can be happened because of Pr doping that gives rise to the modification of electron structure and the hybridisation of the energy levels.

A widely used approach to reduce the charge recombination and improve the performance of a silicon based Schottky barrier solar cell (SBSC) is to use an interfacial layer between metal and Si. In the present work we have investigated the role of graphene oxide (GO) as interfacial layer for p doped Si (p-Si) based SBSC utilizing AZO (Aluminum doped ZnO) as transparent top contact. The not obvious compatibility of the different layers combined in the solar device results clear from the improvement of all the electrical parameters measured in the AZO/GO/p-Si solar cell respect to the simple AZO/p-Si device used as reference. In particular dark IV characterization put in evidence the majority carrier blocking properties of the GO in this type of structure, with an increment of 140 meV in the barrier height respect to the device without GO, resulting in a 100% enhancement in the final solar cell efficiency.

A triple p–n junction Si photodetector using 0.25-μm standard CMOS process at 650- and 850-nm wavelengths is presented and investigated. Triple p–n junctions are formed vertically by n⁺-implant/p-well (N+/HVPW), p-well/n⁺-buried layer (HVPW/NBL), and n⁺-buried layer/p-substrate (NBL/P-sub) junctions to attain a wavelength-dependent response. The responsivity and pulse response were characterised in different bias schemes. Measured photocurrents from HVPW/NBL and NBL/P-sub junctions under reverse biasing and a floating electrode on N+-HVPW showed the smallest FWHM values. The −3 dB bandwidth of 1.9 GHz converted from pulse measurement is the highest result ever reported in 654-nm wavelength using standard CMOS technology. The proposed triple p–n junction Si photodetector with bias schemes shows combined excellent performance in 650- and 850-nm wavelengths.

In this reported work, TiO2 nanoparticles containing anatase-rutile and pure rutile phases were prepared by sol–gel and hydrolysis in acidic solution methods, respectively. Two general procedures, doping during synthesis (DDS) via a hydrolysis method and doping on the provided TiO2 nanoparticles (DOP) that is performed by the impregnation method have been studied by doping copper to these nanoparticles. The photocatalytic activity was evaluated by photodegradation of C.I. Acid Red 27 as a model contaminant. The prepared samples were characterised by X-ray diffraction, atomic absorption flame emission spectroscopy and scanning electron microscopy. It is found that the photosensitised degradation activity can be enhanced by doping an appropriate amount of Cu. Photocatalytic activity results indicated that samples that have been doped by the DDS procedure show higher photocatalytic efficiency than samples doped by the DOP procedure.

N, C-codoped BiOCl (BiOCl–NC) flower-like hierarchical structures were synthesised by an one-pot solvothermal process and characterised by X-ray diffraction patterns, X-ray photoelectron spectroscopy, UV–vis diffuse reflectance spectra, transmission electron microscopy and high-resolution transmission electron microscopy. As-synthesised BiOCl–NC showed higher photocatalytic activity in an aqueous RhB photodegradation system than pure BiOCl under visible light irradiation. The trapping experiments of active species during the photocatalytic reaction showed that the photocatalytic degradation of organic pollutants in the BiOCl–NC system proceeds through direct hole transfer and O₂^•− rather than •OH.

Al-doped ZnO nanoparticles have been synthesised via sol–gel method. Aluminum nitrate and aluminum chloride, as two widespread doping sources, have been compared in various Al/Zn molar ratios of 0.1, 0.5, 1, 2 and 5. After sol preparation, all samples with different Al content have been aged and then dried at 120°C. The resultant grinned powders calcined at different temperatures of 400, 500, and 600°C. X-ray diffraction (XRD) method has been used to investigate crystallisation behaviour and structural properties of samples. Less crystallinity in chloride source samples is detected compared to the nitrate source; however, identical distortion of hexagonal wurtzite unit cell in both sources was evident in XRD results. Field emission scanning electron microscopy demonstrates semisphere morphology of ZnO nanoparticles with particle size less than 60 nm. Fourier transform infrared spectroscopy was conducted to find possible chemical reactions and complexes during the sol–gel process in different Al source samples. UV-vis spectroscopy was carried out to find optical properties of the Al:ZnO samples. The results represent different optical properties in Al chloride and Al nitrate sources.

The atmosphere compensating technique with an individual selenium source is, first, used in the growth of phosphorus-doped p-type ZnSe nanowires. The morphology and structure characterisations reveal that the as-synthesised ZnSe nanowires have a wurtzite structure with a diameter of about 160 nm, a growth direction of [001]. The electrical properties’ characterisations demonstrate that the selenium atmosphere compensation technique assisted with phosphorus-doping leads to a substantial action in p-type conductivity of ZnSe nanowires with a high mobility of 1.25 cm² V⁻¹ S⁻¹ and carrier concentration of 1.47×10¹⁸ cm⁻³. The photoluminescence measurements show a dominant emission and two donor–acceptor pair emission.

This paper gives detailed view on the Nanoelectronics and the approaches adopted for improving the speed of the device without compromising the performance. Performance of the device is mainly based on the speed of operation, Operating voltage and size of the device. In the recent years the two main approaches adopted for optimizing the device performance are new and modified device architectures and using alternate materials which are different from the normal materials used for electronics. Device structures have been modified and designed according to the application. Device modelling is the approach adopted by various companies and research groups in the universities to modify and design new device structures using device modelling and simulation software's. Performance of the device can be improved by using alternate materials such as GaAs, ZnO, BiTe, In, TiO, Fe, Co, Al, Zr etc. Materials other than silicon and germanium with better optoelectronic and electronic properties have been used to improve the performance of the device. The property of the materials can be improved by doping different materials at different compositions and preparing nanomaterials by using different preparation techniques. Materials property is analyzed by using different characterization techniques such as XRD, SEM, TEM, UV, LCR, etc.

A commercial silicon-based variable optical attenuator has been converted to a low bandwidth (quasi-CW) light monitor through an ion implantation and annealing process. The measured total optical loss of the device is <5 dB while the responsivity per tapped fraction is 1 mA/W/dB. The straightforward manner in which the monitoring functionality is induced suggests a cost-effective route to CW optical monitors using a widely available commercial product.

A number of GaAs-based long-wavelength, vertical-cavity, surface-emitting laser structures with optical and electrical confinement based on selective area epitaxy have been fabricated and evaluated. The influence on output power, threshold current, thermal stability and modal properties from design parameters such as bottom-distributed Bragg reflector (DBR) doping, cavity doping, dielectric top DBR design and carrier confinement barriers is evaluated. More than 7 mW of output power is emitted from multimode devices with a square active region size of 10 µm. Single-mode power from smaller devices is restricted to 1.5 mW because of a non-optimal cavity shape.

A high-growth-temperature GaAs spacer layer (HGTSL) is shown to significantly improve the performance of 1.3 µm multilayer InAs/GaAs quantum-dot (QD) lasers. The HGTSL inhibits threading dislocation formation, resulting in enhanced electrical and optical characteristics and hence improved performance of QD lasers. To further reduce the threshold current density and improve the room-temperature characteristic temperature (T₀), the high-reflection (HR) coating and p-type modulation doping have been incorporated with the HGTSL technique. A very low continuous-wave room-temperature threshold current of 1.5 mA and a threshold current density of 18.8 A cm⁻² are achieved for a three-layer device with a 1 mm HR/HR cavity, while a very low threshold current density of 48 A cm⁻² and a negative T₀ are achieved in the p-doped lasers.

The segmented contact method is used to study the performance of intrinsic and p-doped quantum dot structures emitting at 1.3 µm. From measurements of the absorption, it is shown that despite being doped to a level of 18 acceptor atoms per dot, only 19% of the quantum dot states are filled by excess holes, illustrating the importance of the continuum states in the wetting layer. We directly measure the modal gain and non-radiative recombination and show that the modal gain is increased as a function of transparency point when p-dopants are introduced without a significant increase in non-radiative recombination. These results explain the 65% reduction in threshold current observed for uncoated 1500 µm long devices at 300 K.

The aim of the authors is a performance comparison of quantum dot infrared photodetectors (QDIPs) with quantum well infrared photodetectors (QWIPs) under various operating conditions. This type of photodetector is interesting from the point-of-view that QWIPs have numerous advantages over photodetectors based on HgCdTe. From a quantum structure point-of-view, QDIPs have several advantages over QWIPs, especially their wide spectrum range that can be covered, as well as the availability of absorption normal incident light. However, they still have some problems that include high values of dark current and lower values of their responsivity. For these reasons, there is a need to make a theoretical comparison between the two fundamental types of quantum photodetectors. The more interesting parameters of these detectors to achieve this comparison are calculated. These parameters include dark current, photocurrent, responsivity and detectivity. Numerical results show that QDIPs have a lower value for their responsivity and detectivity for the same operating conditions. The aim is to reduce the dark current by adjusting the doping level of these detectors. Moreover, the effect of lateral size and its associated adaptive value can improve the behaviour of the QDIPs that are processed to some extent.

The fabrication and characterisation of a monolithic extended cavity ridge laser using low-energy ion-implantation induced quantum well intermixing on InGaAs/InGaAsP quantum-well structure are presented. An extremely low propagation loss of 2 cm⁻¹ in the passive waveguide section has been measured.

An n-InAsSb/p-GaSb tunnel junction for intra-device contacts with an extremely low contact resistivity of 2.4×10⁻⁶ Ω cm² is reported. Both sides of the junction were doped with silicon, using the amphoteric nature of the dopant for n- and p-type doping. This should provide long-term stability of the device.

Two of the most important intermixing techniques, ion implantation and impurity free vacancy disordering, are investigated and compared in InGaAs/(Al)GaAs quantum well (QW) and quantum dot (QD) structures. For ion implantation induced intermixing, arsenic implantation was performed and the amount of interdiffusion created was found to vary as a function of implantation dose and temperature. Impurity free vacancy disordering was also enhanced by deposition of SiO₂ in both QW and QD structures and annealing at different temperatures. In order to obtain large differential energy shifts for device integration using both methods, the essential issue of suppression of thermal interdiffusion using a TiO₂ capping layer was also addressed.

A proton-implanted photonic crystal vertical-cavity surface-emitting laser for fibre optic applications is demonstrated. Ultra-low threshold current of about 1.25 mA, single fundamental mode (SMSR>40 dB) CW output power of over 1 mW, with a pulsed output power exceeding 2 mW has been achieved in the 850 nm range.

Optical studies of GaAs_1−xN_x/GaAs and B_xGa_1−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 B_xGa_1−xAs alloys compared to pure GaAsN structures.

Epitaxial growth and characterisation of Ga_1−xIn_xAs_1−yN_y films and quantum wells are presented. Starting with the epitaxy on GaAs, recent results on the local bonding of nitrogen in Ga_1−xIn_xAs_1−yN_y 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 Ga_1−xIn_xAs_1−yN_y 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 Ga_1−xIn_xAs_1−yN_y 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 Ga_0.22In_0.78As_0.99N_0.01 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.

Passivation of GaAs by silicon nitride (Si_xN_y) deposition using low-frequency PECVD (LF PECVD) is presented. The high amount of hydrogen implantation during this process enhances the passivation effect, demonstrating for the first time the unpinning of the Fermi level by a simple deposition of Si_xN_y on a deoxidised GaAs surface. The (NH₄)₂S/Si_xN_y passivation is also simplified, and MIS capacitors are fabricated by a novel process, which consists in exposing the GaAs surface directly to sulphur solution, without the usual deoxidation etching step, followed by the deposition of LF PECVD Si_xN_y. Good modulation of the surface potential is observed, and the interface state density (D_it) as measured from 1 MHz C–V characteristics has a minimum of 3×10¹¹ cm⁻² eV⁻¹.