The paper theoretically analyzes properties of graded-band-gap (GBG) p-n structures in which band gap linearly enlarges with increasing the distance from the junction metallurgical edge. It is shown that by means of band-gap grading one can significantly reduce the diffusion reverse current caused by carrier thermal generation in the structure base regions and Ohmic contacts. The numerical estimations have been made for the case of p-n junction on the basis of CdHgTe solid solution.

Compounds of the type M(S2CNRR’)2, M = Ni(II), Pd(II), RR' = Et2, MeEt and MenBu, have been synthesized and used as single-source precursors for the fabrication of NiS and PdS thin films via low-pressure (LP) metal-organic chemical vapour deposition (MOCVD). The phase of nickel sulfide films deposited on glass substrates was found to be NiS1.03 or a mixture of NiS1.03 and NiS, whilst palladium sulfide films were only tetragonal PdS. The films have been characterized by X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), transition electron microscopy (TEM) and energy dispersive analysis of X-rays (EDAX).

Thermodynamic analysis of the vapor phase over ZnGeP2 in Zn-Ge-P-Cl system has been carried out. The analysis showed that this system can be used for the vapor growth of ZnGeP2. Homoepitaxial layers of ZnGeP2 were grown in a closed system using chemical vapor transport. Electrical and photoluminescence properties of the layers were studied, and crystal lattice parameters were measured. Comparison of properties for bulk and vapor grown ZnGeP2 crystals were carried out. It was found that the vapor grown crystals have more perfect structure than the bulk ones, particularly, they have significantly lower vacancy concentration.

A preliminary device was investigated as a first step in making an on-chip electrical readout based on the semiconductor CdS for a novel 3-D optical data storage method. The optical data is stored in glass as subsurface nanometer size defects called voxels. These voxels display secondary harmonic generation (SHG) to 800 nm input light. The device begins with an indium tin oxide film on a glass substrate coated with a film of Al2O3. In this preliminary device the Al2O3 was patterned via optical lithography with a periodic array of 10 micron holes that were filled with electrodeposited CdS. X-ray diffraction, and energy dispersive X-ray analysis were used to characterize the CdS. The device operation depends on the ability of the CdS with a bandgap of 2.4 eV to detect the 3.1 eV SHG light from the voxels while remaining unresponsive to 1.6 eV input light. The electrodeposited CdS was found to absorb 400 nm light at least a factor of 10 times greater than 800 nm light. Light to dark photocurrent ratios of 15 to 63 were observed from the CdS pillars using a 150 W xenon broadband light source. A light to dark ratio of about one was found when a long pass optical filter allowed only wavelengths above 750 nm. Thus the 10 micron CdS pillars have detected 400 nm light while rejecting the 800 nm input light.

We prepared othorhombic β-FeSi2 thin-films on Si(111) substrates by a pulsed laser deposition method (PLD) and studied the relationship between bandgap energy and composition ratio by themal annealing of β-FeSi2 thin-films on Si substrate. When the substrate temperature was 500·°C, β-FeSi2 thin-films were grown on Si(111) substrates. The sample prepared on Si(111) substrate was a monocrystalline structure since only (220) or (202) signals of β-FeSi2 were observed. A large amount of defects existed in the thin film. These defects were reduced by using high temperature and long time annealing. Heat treatment of 20 hours or more time was effective for reducing diffect. The iron diffusion of β-FeSi2/Si interface was observed by RBS spectra. Composition ratio of the prepared β-FeSi2 was Fe:Si=30:70. As-deposition β-FeSi2 was Si-rich. The p-n diode characteristics of these heterostructure diodes were investigated by C-V measurements. β-FeSi2/Si interface prepared by 400· °C was an ideal one-side step junction. The surface roughness was decreased by annealing.

A series of epitaxial single crystal ZnO samples were grown by Pulsed Laser Deposition (PLD) on c-axis, double-side polished sapphire at temperatures ranging from 600°C to 800°C. A comprehensive optical study, consisting of cathodoluminescence (CL) and transmission spectroscopy measurements, was performed before and after annealing the samples in air and oxygen environments. The structural characteristics of the films were observed by x-ray diffraction and transmission electron microscopy (TEM). Using these measurements, the data revealed that annealing significantly improved the luminescence and exciton line-width of the better material grown at the higher end of the temperature range. In lower quality samples grown at the lower end of the temperature range, the optical quality of the material was degraded. In the samples grown at higher temperatures, annealing improved the optical qualities. An increase in the below band-gap, green band emission was also observed under some annealing conditions.

Metal-induced low temperature (≤ 550 °C) crystallization of a-Si1-xGex (0 ≤ × ≤ 1 ) layers on SiO2 films has been investigated. For low Ge fractions below 20 %, Ge-doping enhanced plane growth was observed. This realized strain-free poly-Si0.8Ge0.2 films with large grains (18 μm). On the other hand, dendrite growth was dominant for intermediate Ge fractions with 40–60 %. Directions and widths of dendrites became straight and narrow with decreasing annealing temperature. As a result, very sharp needlelike crystals (width: 0.05 μm, length: 10 μm) were obtained at the optimized growth conditions (x: 0.4, annealing: 450 °C, 20 h). These new polycrystalline SiGe films on insulators should be used for the advanced system-in-displays and novel one-dimensional wires.

Electrothermal-Chemical Synthesis (ETCS) is a relatively new process for the synthesis of nanocrystalline powders. With ETCS nanoparticles are formed through the controlled chemical reaction of a metal plasma, produced by cathode erosion, with a gas. By controlling the quench rate of the plasma precisely, the average particle size can be varied from as small as 6–8 nm up to 100 nm and above. The process is quite versatile and can be used to produce a wide variety of nanopowders including metals, oxides, and nitrides. However, before the nanoparticles produced by this process (or any other process for that matter) can find wide scale commercial acceptance, their physical properties must be characterized. Among many characterization techniques, electron microscopy can provide structural, chemical, and morphological information on nanoparticles. In this paper, we will discuss the SEM and TEM characterization of metal and metal oxide nanoparticles powders produced by ETCS.

We report on light and heat distributions in the active area of infrared lasers and light-emitting diodes operating at 300 K in the 0, 8–4,7 μm spectral range. To separate light and heat produced by these devices, we developed a high-resolution multi-spectral infrared (<1 m, 3–5 m and 8–12 m ranges) “vision” facility capable of providing <20 m spatial resolution and 10 s temporal resolution. We show how current crowding and Joule heating combined drastically decrease integral power emitted by light-emitting diodes and provoke remarkable non-uniformity in light and heat maps. As concerning stripe lasers, we comment on heat spreading and heat bottlenecks inside the laser dome and quality of heat sink.

A high power conversion efficiency above 1% from a bulk crystalline silicon (c-Si) light-emitting diode (LED) has been demonstrated at near room temperature. These devices are based on normally weak one- and two-phonon assisted sub-bandgap light emission processes. Their improved performance results from device designs that take advantage of enhanced light absorption by a light trapping scheme which was developed for high efficiency silicon solar cells, and from reducing scope for parasitic non-radiative recombination within the diode. Each feature individually is shown to improve efficiency by a factor of ten, accounting for an improvement by factor of one hundred compared to baseline devices.

Also demonstrated is a greatly improved band-edge light emission and detection using bulk c-Si diodes. A bulk c-Si LED is combined with a similar diode used as a detector that collects the light emitted with a high quantum collection efficiency of 33%, to produce a silicon to silicon optically coupled system that demonstrates 0.18% coupling quantum efficiency. The crystalline silicon LED demonstrates similarly high performance at very low power levels, where it has even higher power efficiency than a high efficiency GaAlAs LED.

Electric field – induced effects are studied in thin films of amorphous Si grown by magnetron sputtering performed in continuous and pulse modes. Current-voltage characteristics are measured under the room temperature in different spectral ranges. It is shown that the investigated dependencies are of exponential character in all range of applied bias. Good photosensitivity was revealed by the samples prepared in continuous mode in the near-IR and visible interval. The samples grown by the pulse magnetron technology were shown room-temperature photosensitivity in near-IR range after 2000C hydrogenation.

We present results on growth and fabrication experiments of AlN/AlGaN superlattices for ultraviolet (UV) optoelectronic devices. Superlattices with extremely short periods have been studied. The AlN “barrier” layers are 0.5 nm thick, and the AlxGa1-xN “wells” are 1.25 nm thick, with x ∼ 0.08. This combination gives an average AlN mole fraction of 0.63 across one full period. The superlattice periods, AlN mole fractions, and energy gaps are determined using TEM, X-ray diffraction, and optical reflectance. They are all consistent with each other. For device fabrication, p-i-n structures are grown doped with Si (n-type) and Mg (p-type). The acceptor activation energy of ∼ 0.2 eV is found. Mesa structures are plasma etched using chlorine chemistry. Etch rates of AlN are ∼ 1/3 those of GaN under identical circumstances. Etch rates of 250 nm/min are used for the device structures. A light emitting diode, with primary emission at 280 nm is reported, and a detector with sensitivity edge at 260 nm are reported.

Bulk crystals of CdGeAs2 have been characterized using photoluminescence (PL), optical absorption, Hall effect, and electron paramagnetic resonance (EPR) techniques. An absorption band near 5.5 microns at room temperature is observed in all of the p-type samples we have studied. A correlation between the magnitude of this optical absorption and the excess hole concentration at room temperature is established. Also, an EPR signal is found to correlate with the strength of this absorption band. PL data are consistent with an increased concentration of shallow acceptors being present in high-absorption samples. From the EPR data, we suggest that a model for the paramagnetic defect associated with the absorption at 5.5 microns may be an acceptor on an anion site.

Chemical bath deposition (CBD) techniques for the growth of CdS polycrystalline thin films are now well developed. However, there usually appear different structures, grain sizes and energy gaps in CdS polycrystalline films by CBD, which implies that the influence of growth process on the structures and properties of CBD CdS thin films must be considered. In this paper, the optical, compositional and structural properties of CBD CdS thin films in the reaction process have been studied by XRD, AFM, XPS and optical transmission spectra measurements. The results can be explained using atomic mechanism and lattice transition in the CdS thin films.

We report on photoreflectance measurements performed in the 0.8–1.6 eV photon energy range in as grown and hydrogenated InxGa1-xAs1-yNy/GaAs single quantum wells grown on GaAs substrates by molecular beam epitaxy. In the hydrogenated samples, a blue-shift of all the QW spectral features and a surprising change with temperature in the nature of the lowest energy transition are found. These features are related to the interaction of H with N atoms. An increase in the binding energy of the heavy-hole exciton upon N introduction into the InxGa1-xAs lattice has been measured also and explained in terms of an increase in the electron effective mass.

An electrically pumped 1.24um GaxIn1-xAsyP1-y Vertical Cavity Surface Emitting Laser (VCSEL) has been designed and simulated. Threshold gain of 153cm-1 and threshold current of 1.00mA was obtained. The external efficiency predicted is 0.31. Also the optimized design of VCSEL structure is presented in this article. GaInAsP and AlInAs constitute the Distributed Bragg Reflectors (DBRs) multilayer stack. Reflectivity of the top DBRs is 0.97 and reflectivity of the bottom DBRs is 0.9978 and is shown to provide a good resonant cavity and sufficient lasing intensity. Compared with other reported structures, the present VCSEL has a lower threshold current and higher threshold gain.

Conjugated polymers are very interesting for light emitting diodes. Further improvement in device performance requires a better understanding on the correlation between the polymer structure and device characteristics. A mesoscopic study using a generalised Monte Carlo method of bipolar charge transport in thin poly(p-phenylene-vinylene) (PPV) films is presented in this paper. We show that energy and spatial molecular disorder have a serious influence on migration of charge carriers within the polymer layer. The transfer of carriers between two polymer chains is made dependent on the chemical potential difference as well as on other features such as the distance between both molecules involved and the direction of the electric field. The purpose of the present work is to clarify the effects of local energy and polymer structural disorder on current flow, trapping and recombination on polymer based devices.

The compound [MeCd(SePiPr2)2N]2 is used as a single-source precursor to cadmium selenide films in a low-pressure chemical vapour deposition process. Thermogravimetric analysis (TGA) shows that the precursor is reasonably volatile, making it suitable for the deposition of thin films. As-deposited films were identified as CdSe confirmed by X-ray powder diffraction (XRPD) and their morphologies were studied by scanning electron microscope (SEM).

A Raman scattering study for self-organized Ge dots on Si substrate is presented. Raman signals from the Ge islands and Si substrate have been separated, by means of difference Raman spectroscopy technique. The wetting layer thickness and strain were estimated from the line width and the position of the peak. The estimated wetting layer thickness values are comparative with the Ge dot height obtained from microscopy measurements. As explained, the strain is observed to decrease with an increase of the Ge island height and the wetting layer thickness.

The paper discusses some recent developments in the GaSb/GaInAsSb/GaAlAsSb heterostructure epitaxial growth and fabrication of GaInAsSb/GaAlAsSb photodiodes for the 0.9–2.55 μm spectral range.