High quality epitaxial films of ZnSe and ZnSe/ZnS strained layer superlattices (SLS) have been grown on (100) GaAs substrates using diethylZinc, dimethylSelenide, diethylSelenide, and propyleneSulfide as reagents in both atmospheric and low pressure environment. This source combination produces the results showing the influence of process conditions, such as reagent flow ratio (fv1/f11) and substrate temperature, on the film stoichiometry, surface morphology, and crystalline quality. Low temperature photoluminescence (PL), Rutherford backscattering spectrometry (RBS), cross-sectional TEM, and x-ray diffraction have been used to characterize the films. Photoluminescence studies at 2.8 K on samples of ZnSe/ZnS strained layer superlattices; 10 periods ZnSe(1.5 nm)/ZnS(8.5 nm), have shown quantum size effect with the peak energy blue-shifted to 3.03 eV with the FWHM=73 meV. Atomic force microscopy (AFM) was applied to study surface morphology of multilayer samples.

Data from numerous LMMS analysis of specimens of a polished sample of CdTe crystal are treated statistically to estimate the accuracy and reproducibility of quantitative analysis. The data are consistent with the instrument producing a fixed condition in plasma for a given laser power. The plasma chemistry is shown to control the conditions reached in the plasma for a given power.

The semiconductors of zinc blend structure are promising candidate materials for numerous experimental and theoretical investigations. In recent years, considerable effort has been made to study the lattice infrared absorption spectrum of II-VI compounds, renewed interest has been taken in CdTe owing to its relatively high electro - optic coefficient in the near infrared. In addition, its nonlinear response to two-phonon absorption in the infrared region is of interest because the material is transparent in this spectral region.

We examine native-defect compensation, solubility limits, and dopant self-compensation in ZnSe. Our results are based on a formalism, using first-principles density-functional theory, that treats dopant atoms and native defects on an equal footing. For the case of acceptor doping of ZnSe with Li, we find that compensation due to interstitial Li donors and to native donor defects can be reduced to a tolerable level by carefully adjusting the growth conditions. A more serious impediment to Li doping comes from the solubility limit of Li in ZnSe.

Electronic applications of diamond require control over native defects as well as the ability to dope it p- and n-type. B is an excellent p-type dopant, but n-type doping has proven very difficult. Diamond films have also been very difficult to anneal, indicating a high activation energy for self-diffusion. We have investigated the properties of native defects and impurities through large-scale band structure and Car-Parrinello calculations. We indeed find that the activation energy for self-diffusion is very high in the intrinsic material, but it decreases by as much as 3 eV in either p- or n-type material. P, Li, and Na are shallow donors, but their solubilities are too low for incorporation into diamond through in-diffusion. It is energetically favorable for B and N to dissolve in diamond, which explains their prevalence in natural diamond. The calculations explain for the first time the reasons for the distortion of atoms around N from the fully tetrahedral site, as well as why N is a deep rather than a shallow donor. We also consider the effects of simultaneous doping with N and B on the thermodynamic equilibrium between diamond and graphite.

Material growth is an inherently non-equilibrium process. However, thermodynamic considerations often provide important insight into material growth, the structure of grown materials, and process control parameters. In essence, thermodynamic considerations are important when activated processes are either slow or fast on the time scale of the growth. Activated kinetic processes are important when their time scale is the same as that of growth. Realistic ab-initio calculations of material structure and dynamics can provide a microscopic understanding of both thermodynamics and the kinetics of material growth. The primary focus of this article is a recently proposed defect-assisted multiple-regrowth stabilization of cubic phases. in this theory the incorporation of vacancies at the growth face changes the relative binding energy of cubic versus hexagonal phases so that diamond and cubic boron nitride can nucleate and grow. This theory predicts that diamond nucleation and growth is enhanced under electron rich or positive ion conditions. Experimental results on growth of both diamond and cubic boron nitride that motivate and support theoretical predictions are described. Cubic boron-nitride grows under off-stoichiometric conditions. The nucleation rate of diamond is increased by many orders of magnitude when a flux of electrons impinges upon the surface. Raman line broadening and ESR measurements indicate the presence of significant concentrations of point defects. Predictions and experimental evidence for both n and p type doping will be discussed. Ab-initio calculations of key kinetic processes and thermodynamic quantities for diamond and boron nitride growth are described.

We present a theoretical formalism to investigate doping efficiencies of impurities in semiconductors, and show results for various acceptor impurities (Li, Na and N) in ZnSe. These results, obtained from first-principles calculations, yield important insights in the mechanisms that govern impurity formation energies and solubilities.

Most compound semiconductors crystallize in the zincblende or the wurtzite structures. In both cases, all the host atoms are tetrahedrally coordinated. However, the two lattices have no high symmetry interstitial sites in common. As a result, the stability, lowest-energy configuration, electronic structures, and barriers for diffusion of interstitial impurities are in general very different. This situation is illustrated here in the case of interstitial H in 3C (zincblende) and 2H (wurtzite) SiC. The results can be used to obtain the properties of H in other hexagonal polytypes, in particular 6H-SiC.

Potential energy surfaces and electronic structures of interstial oxygen (Oi) in cubic C, Si, AIP, SiC, and BN have been calculated. The equilibrium site is a bent-bridged bond. In compound semiconductors, Oi has a larger degree of bonding with the most electronegative of the host atoms (P, C, or N) than with the least electronegative one. In addition to the barrier for rotation of O, about the < 111 > axis, which does not involve breaking a bond, we calculated the barriers for migration between adjacent bond-centered sites. There are two such barriers in compound semiconductors. In order to estimate the relative stability of Oi in the various hosts, we calculated the energies involved in inserting O2 into the lattice and dissociating it into two isolated Oi's.

Total energy and band structure results of linear-muffin-tin orbital calculations within the atoiuic-spliere-approxiiuation are presented for SiC, GaN and A1N in the zincblende and the wurtzite structure. We discuss the origin of the directness or indirectness and the relative magnitudes of the band gaps.

We study the Burstein-Moss shift (BMS) in quantum wiies and quantum dots of wide-gap semiconductors, taking Ge as an example, it is found that the BMS increases with increasing electron concentration in a ladder like manner. The numerical values of the BMS is greatest in quantum dots and least in quantum wells. The theoretical analysis is in agreement with the experimental results as given elsewhere.

in this paper we study the Einstein relation in superlattices of wide-band gap semiconductors under crossfield configuration and the for.-ning materials incorporating spin and broadening of Landau levels, it is found, taking GaAs/AÀAs superlattice as an example that the diffusivity-mobility ratio increases with increasing electron concentration and oscillates with inverse quantizing magnetic field due to SdH effect. Thetheoretical analysis is in agreement with the suggested experimental method of determining the same ratio in degenerate materials having arbitrary dispersion laws.

The method for controlling the electrical properties of n-type GaN and AIGaN have been established. Both GaN and AIGaN films having p - type conduction have been realized for the first time. High quality AIGaN/GaN mu I t i-he t er ostrueture showing clear quantum size effect has been fabricated. P-n junction type UV/blue LED with double he t e ros t rue ture have been developed for the first time.

The nitrides of Al, Ga and In are III-V compound semiconductors with properties more closely akin to those of the II-VI system and applications problems of similar type. All three have wide, direct band gaps and relatively light, therefore mobile, electrons. Less encouragingly, native point defects appear to play a significant role in both optical and electronic properties.

Both experiment and theory point to a triplet of donor states associated with the nitrogen vacancy, with deep compensating centres deriving from antisite defects. The ionic radius of the metal then seems to determine the conductivity of as-grown material, indium is reluctant to occupy nitrogen sites while aluminium does so readily and gallium is equivocal. Thus the upper donor level of InN is not depleted and n-type behaviour is always observed, the equivalent level in AIN is always overcompensated and the remaining donor levels are too deep to contribute free electrons at normal temperatures so that the material is consistently insulating. GaN may be n-type or semi-insulating since compensation ratios either side of unity appear to be possible, depending on the method of growth.

In this paper we review the evidence, both optical and electrical, for the existence, nature and energetic location of the four basic point defects in each nitride, noting in particular that all four broad luminescence bands in GaN:Zn can be accounted for by the presence of nitrogen on gallium sites and of nitrogen vacancies.

Extensive and systematic studies on reactive magnetron sputtering of InN thin films are summarized. The films have been deposited onto several types of substrates, with variations in such process parameters as deposition temperature, partial pressures of reactive and inert gases, sputtering power and gas flows. These films have been characterized by measuring their electrical, optical, structural and morphological properties. It has been shown that epitaxial growth of InN occurs on the basal plane of single-crystal (00.1) sapphire and (001) mica substrates and on the (111) face of cubic substrates such as silicon and zirconia.

Two principal problems currently limit the usefulness of thin films of InN. First, although epitaxy can be attained with the proper choice of substrate type and deposition temperature, the resulting film is an agglomerate of epitaxial grains -- not a single crystal. Second, all magnetron sputtered InN films prepared to date have low mobility and high carrier concentration (likely due to nitrogen vacancies). In an attempt to address these problems, experiments on the growth and characterization of sputtered InN films have been carried out and are discussed here with particular emphasis on seeded heteroepitaxial growth and the effects of film deposition temperature.

For example, it was found early that the growth of InN on the bare surface of several crystalline substrates at growth temperatures near 350°C results in a morphological transition that causes a degradation of semiconducting properties. The predeposition of an AIN seed layer inhibits this morphological transition and stabilizes a relatively high mobility state, but a still too high carrier concentration obtains. Further progress critically depends on optimizing the seeded heteroepitaxial growth technique in conjunction with the achievement of InN films with lower density of nitrogen vacancies.

The low temperature deposition (400–650° C) of AlxGa1-xN films by metalorganic chemical vapor deposition (MOCVD) was characterized. Triethylgallium (TEG), trimethylaluminum (TMA), and ammonia (NH3) served as the precursors and both sapphire and silicon as the substrates with helium as the carrier gas. The deposition was operated at the atmospheric pressure. The crystallinity was improved even at low temperatures when AlxGal-xN was grown on a thin buffer layer of A1N at 400° C. With an AlxGa1-xN/AIN layered structure, epitaxial growth of AlxGa1-xN was obtained at 650° C on sapphire substrates. Auger results showed that the Al fraction x was less than 0.1. X-ray diffraction indicated a strong peak at 2θ =34.9 degrees for the (0002) planes from the film on sapphire substrates. The electron channelling pattern (ECP) of the film produced at 650° C revealed a 6 fold symmetry contrast pattern indicating the epitaxial growth of the film. Photoluminescence (PL) showed a dominant emission at 353 nm for the film on sapphire substrate. Surface morphology examined by SEM was featureless for the film produced at 500° C, while a relatively rough surface can be seen on the film produced at 650° C (5, 000x). The band gap was measured as 3.56 eV. The Al mole fraction x in the alloy was observed to be lower than that in the gas phase.

GaN films were grown on c-plane (0001), a-plane (1120) and r-plane (1102) sapphire substrates by the ECR-assisted MBE method. The films were grown using a two-step growth process, in which a GaN buffer is grown first at relatively low temperatures and the rest of the film is grown at higher temperatures. RHEED studies indicate that this growth method promotes lateral growth and leads to films with smooth surface morphology. The epitaxial relationship to the substrate, the crystalline quality and the surface morphology were investigated by RHEED, X-ray diffraction and SEM studies.

Epitaxial GaN films were grown on Si(001) and (111) substrates, using a two-step process. The films on Si(001) are single crystalline having the zincblende strucutrue, while those on Si(111) have the wurtzite structure. The crystalline qualities of the films were studied by X-ray diffraction. While the zincblende GaN has a perfect cubic structure, the wurtzitic GaN on Si(111) has a considerable amount of stacking faults along (0002) direction, which gives rise to significant zincblende component with (111) orientation. Room temperature resistivity for both type of GaN films was found to be larger than 100 Ω· cm. The temperature dependence of th resistivity gives a defect level at HOmeV for wurtzitic GaN and 80meV for cubic GaN. Optical studies show that GaN on Si(001) has a gap 3.2eV, and GaN on Si(111) has a gap of 3.4eV at room temperature.

The seeded-heteroepitaxial growth, morphology and electrical transport properties of InN overlayers deposited by reactive magnetron sputtering on AIN-nucleated (00.1) sapphire have been investigated. For comparison, InN films were grown directly onto (00.1) sapphire under identical experimental conditions. These unseeded films showed a unimodal growth and were a mixture of textured and broadly heteroepitaxial grains. Low Hall mobility and carrier concentration and high resistivity were typical. In contrast, the AIN-nucleated InN overlayers exhibited a bimodal growth, strongly heteroepitaxial grains, and high Hall mobility. A particularly interesting aspect of the films grown on seeded (00.1) sapphire is the preservation of electrical continuity and high Hall mobility even in the limit of InN overlayers with thicknesses only on the order of 20–40Å.

Gallium nitride thin films were prepared by atmospheric pressure chemical vapor deposition from hexakis(dimethylamido)digallium, Ga2(NMe2)6, and ammonia precursors at substrate temperatures of 100–400 °C with growth rates up to 1000 Å/min. The films were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry and forward recoil spectrometry. The N/Ga ratio varied from 1.05 for films deposited at 400 °C to 1.5 at 100 °C. The hydrogen concentration increased from 10 atom % for films deposited at 400 °C to 24 atom % at 100 °C. Films deposited at 100 °C were amorphous but films deposited at higher temperatures were polycrystalline. Bandgaps of the films varied from 3.8 eV for films deposited at 400 °C to 4.2 eV at 100 °C.