Tantalum and tantalum suicide contacts were investigated as high temperature rectifying contacts on type MB natural diamond. Tantalum and silicon were co-sputtered using DC and RF planar magnetrons, respectively. Current-voltage measurements of tantalum suicide subjected to various anneals and of pure tantalum contacts were recorded at 50°C intervals up to 400°C which was the desired operating temperature of the rectifying contact. Tantalum contacts to diamond maintained good rectification up to 300°C whereas amorphous tantalum suicide operated well up to 400°C.

Schottky diodes were fabricated from boron doped diamond grown in a turbulent flame. The substrates used were type IIa diamond (100) crystals 1.5 mm in diameter and.25 mm thick. A p/p+ structure was deposited using the p+ layer as an ohmic contact. Current-voltage (I-V) and capacitance-voltage (C-V) measurements were made on the finished devices. An ideality factor of 1.8 was obtained from the I-V characteristics. Doping levels from C-V measurements indicate an acceptor concentration on the order of 5 × 1017/cm3.

The technology to fabricate polycrystalline diamond film resistors has been initiated using modified thick film patterning techniques and in situ solid source doping.

Doping of polycrystalline diamond films in microwave plasma CVD systems has been achieved historically through use of diborane gas, which may contaminate the deposition system causing all diamond films thereafter to be doped p-type. We have attempted noncontaminating in situ doping utilizing two solid source dopants, and have met with preliminary success.

The more effective source (B2O3) produces a fairly even dopant concentration across the substrate, with sheet resistances ranging from 800 ohms per square to 4500 ohms per square. The other source (BN) showed significant doping in a narrow band surrounding the source, but the doping concentration decreased rapidly with distance from the source. Films grown afterwards with no doping were evaluated through resistance measurements; no evidence of doping contamination was observed.

The modification of the wear properties of type Ha diamond following ion implantation with 100 keV carbon and nitrogen has been studied at implantation temperatures of 150 and 470 K. Abrasion testing using low load multiple pass scratch testing with a Rockwell diamond indenter has shown a decrease in wear resistance. Microstructural modifications resulting from ion implantation have been assessed using Channeling Rutherford Backscattering Spectroscopy (C-RBS). No correlation was found between the presence of ion beam induced point defects (as measured by C-RBS) and the increase in wear. There are no obvious wear rate differences observed for nitrogen or carbon implantation.

Vapor pressure control technology is successfully applied to the bulk crystal growth, epitaxial growth and diffusion process of ZnSe crystals. Surface morphology and the crystal quality are investigated by the optical microscope and the X-ray double crystal diffractometry as the function of the growth temperature and the applying Zn vapor pressure. The cathode luminescence is also measured to evaluate the optical properties and the effect of low temperature growth and the application of Zn vapor pressure are demonstrated, p-type ZnSe crystals are grown from the Se solution with group Ia element as a dopant under controlled Zn vapor pressure, p-n junction diodes are also prepared by the Ga diffusion from Zn solution under Se vapor pressure. Emission spectra from the p-n junction and its Zn and Se vapor pressure dependencies are also presented.

Zinc selenide films have been grown heteroepitaxially on Si(100) substrates by molecular beam epitaxy. The initial stages of growth are dominated by the reaction of Se and Si atoms to form the compound SiSe2- The compound formation disrupts epitaxy, and several growth methods which avoid this are described and compared. We find that room temperature deposition plus solid phase epitaxy does not lead to significant SiSex formation and yields uniformly thick films which are misoriented with respect to the substrate and contain large regions of twinned ZnSe. The use of an As monolayer on the Si surface before the start of ZnSe growth allows good ZnSe epitaxy without any Si-Se reaction or any misorientation. ZnSe films have also been used as interlayers for GaAs growth on Si. This has allowed us to obtain uniform GaAs films at thicknesses which typically manifest a coalesced island morphology for GaAs grown directly on Si.

Striking progress in the development of II-VI semiconductor heterostructures, coupled with seminal advances in doping, has very recently led to the first demonstration of blue and blue/green diode lasers operating from cryogenic to room temperature. The active region in these devices was based on the (Zn, Cd)Se/ZnSe multiple quantum wells (MQW) which had earlier been actively studied as a candidate for laser medium by optical pumping techniques. We report on the performance of such MQW diode lasers with emphasis on structural versatility in terms of preparation on both p-type and n-type GaAs substrates, and where sulfur is or is not incorporated for blue/green color lasing. In this work we have obtained pulsed, high power, high quantum efficiency laser emission up to near room temperature conditions. Efficient LED devices are described which operate in the blue (494nm) at room temperature.

Cd1-xZnxTe ZriTe crystals grown by the travelling heater methode (THM) have been investigated by low temperature photoluminescence (PL). The excitonic energy gap as a function of the alloy composition was determined for the complete range of x - 0 to x - 1. The composition dependent broadening of the neutral acceptor bound exciton (A°X) line was measured and compared to theoretical calculations. The Donor - Acceptor pair luminescence in the crystals is a superposition of recombinations due to residual Cu acceptors and A - centers (anion vacancy - donor pairs ).

We have characterized MOCVD grown ZnS layers for thin film electroluminescence (TFEL) devices. Films with thicknesses ranged from several Å to 2 μm were studied by x-ray diffractometry (XRD), cross-sectional transmission electron microscopy (XTEM), high-resolution transmission electron microscopy (HRTEM), and ultraviolet-visible photospectrometry (UVS). From HRTEM micrographs, it was observed that ZnS films consist of a mixture of hexagonal and cubic phases. Correlation of UV absorption spectra with XRD analysis resulted in a method for quantitative determination of the cubic packing fraction of polymorphic ZnS films. The initial ZnS layer (< 1000 Å) deposited on BaTa2O6 had more hexagonal than cubic phase because of denser crystal defects. However, the fraction of cubic phase increased with the film thickness. In addition to film microstructures, the mean grain size, growth rate, film uniformity, and surface roughness of MOCVD grown ZnS thin films as functions of film thicknesses and substrate temperatures were also calibrated by XTEM results.

ZnSe/ZnCdSe diode structures were grown on (In, Ga)As buffer layers by molecular beam epitaxy. Lattice distortions and defect distributions in buffer layers and diode structures were examined by X-ray diffraction and transmission electron microscopy. Diode structrues with low dislocation densities were obtained by the growth on tetragonally distorted In0.043 Ga0.957 buffer layers, the lattice spacing of which is slightly smaller than that of ZnSe.

The (ZnSe) /(ZnS ), strained layer super-lattices (SLSs) on (100) GaAs and (ZnTe)/(ZnSe) SLSs on (100) InP have been grown by molecular beam epitaxy (MBE) and atomic layer epitaxy (ALE). The structural characteristics of these SLSs were investigated in situ RHEED observation, low-angle X-ray diffraction spectra, TED image and AES analysis. The optical properties of the SLSs, such as refractive index of superlattice materials, photoluminescence (PL) spectra, transient PL spectra, Raman spectra, far-infrared reflectivity spectra and Optical nonlinear have been studied.

Spectroscopie ellipsometry is a well developed technique for studying the semiconductor materials and heterostructures. Here, we have applied this technique to in-situ studies of ZnSe and ZnCdSe growth in a low pressure organometallic vapor phase epitaxy system. The growth of ZnSe on GaAs was studied using a light source in the range 2 to 4 eV, and film thickness of a few tens of angstroms could be monitored by this technique. The band gap and the composition of Zn1-χCdχSe could also be measured as a function of real time. It was found that, for a gas phase DMCd composition of 60%, the amount of Cd incorporated in the layers is less than 25%. Spectroscopie ellipsometry is demonstrated to be a valuable technique for in-situ monitoring of semiconductor growth in organometallic vapor phase epitaxy systems.

Pulsed KrF (248nm) laser ablation of a polycrystailine ZnS target has been used to grow high quality, carbon-free, epitaxial ZnS thin films on GaAs(OOl), GaAs(111), and GaP(OOl). The films were grown at temperatures of 150–450°C, using a rotating substrate heater and deposition geometry that produces films with highly uniform thickness. X-ray rocking curves are consistent with (111) stacking faults being the dominant defects in the ZnS films grown on GaAs. The estimated stacking fault density is ∼6 × 1010 cm-3, comparable to the best MOCVD ZnS films. RBS analysis shows that these defects are located predominantly near the GaAs-ZnS interface. The anisotropy of the ZnS growth rate, between the GaAs(001) and GaAs(111) surfaces, was found to be temperature-dependent.

Several series of sodali te analogues of unit cell composition M8X2(TO2)12, where M is Zn or Cd, X is a chalcogen, and T is a tetrahedral cation B, or Be in combination with Si or Ge, have been prepared. An M4X tetrahedron, which is the first coordination sphere of the bulk semiconductor MX, sits at the center of each sodalite cage. These materials have been structurally characterized by solid state 77Se and 125STe MAS NMR and by powder X-ray diffraction. Diffuse reflectance optical absorption spectra are reported for each series. The borates have optical properties similar to the bulk MX whereas the beryllosilicates and germanates exhibit large blue shifts in the absorption spectra.

It has. generally been concluded that good doping in wide-gap semiconductors is best accomplished by non-equilibrium means. Excimer lasers, because of their high intensity and short pulses, are ideal for this. Our earlier laser annealing work on bulk ZnSe resulted in complications due to increased twinning of the sample. Our present work shows that twinning can be eliminated by the use of originally untwinned MBE material. The MBE samples had the additional advantage, over bulk, of a far smoother surface, which simplified the investigation of melting and evaporation. Use of power levels of 10, 20, and 35 MW/cm2 showed no melting at 10 MW/cm2, melting and no detectable evaporation at 20 MW/cm2, and evaporation at 35 MW/cm2. Combined ion beam cratering and SEM examination showed a depth of the melted layer, at 20 MW/cm2, of - 0.5 μm. Moreover, AES analysis showed minimal decomposition of the 20 MW/cm2 sample.

Organometallic vapor phase epitaxial (OM VPE) growth of ZnSe on GaAs was carried out using dimethylzinc (DMZn) and dimethylselenium (DMSe) as source precursors. The growth of ZnSe can be initiated either by introducing DMZn first (Zn stabilized) or DMSe first (Se stabilized).

A systematic study of this growth initiation step on the properties of ZnSe epilayers was carried out using Photoluminescence (PL) and Double Crystal X-Ray Diffraction (DCD) in order to optimize the ZnSe-GaAs interface. PL and DCD data show a considerable difference in lattice relaxation mechanism between Zn and Se stabilized layers. Se stabilized layers are also seen to be considerably tilted with respect to the substrate. PL properties of Se stabilized layers exhibit strong near band edge emission (NBE) and weak deep level emission such as Y0, compared to layers grown by Zn stabilization.

Wide-band gap II-VI semiconductors have direct bandgaps which cover the energy range from the red to the u-v. This makes such compounds ideal for optoelectronic applications. CdS has a band gap of 2.42 eV and becomes potentially useful for the green region of the spectrum. However, because CdS has a preference to adopt the hexagonal wurtzite structure, epitaxial growth of this semiconductor is complicated. Nevertheless succesful growth of CdS layers onto CdTe is possible. We report a detailed photoluminescence study of CdS/CdTe heterostructures grown by CVD. The CdS layers have high quality hexagonal structure. Luminescence lines are narrow enough and we could detect a splitting ocurring on the excited state of a neutral acceptor bound exciton, at 2.5462 eV.

Epitaxial and bulk ZnSe of good structural perfection have been grown by vapor-phase techniques. Epitaxial undoped ZnSe layers were grown by metal-organic chemical vapor deposition (MOCVD) on GaAs {100} substrates in a horizontal-flow quartz reactor chamber. Conventional pyrolytic growth at 450°C was used, with diethyl zinc (DEZn) and diethyl selenium (DESe) reactants transported in hydrogen carrier gas.

Layers with smooth surface morphology and very good crystal structure were obtained, with no evidence of gas-phase pre-reaction. Sharp electron channeling patterns produced in the scanning electron microscope (SEM) indicated that {100}-oriented ZnSe layers were grown on (100) GaAs surfaces, as expected. X-ray rocking-curve analysis with a silicon four-crystal monochrom-ator gave full-width at half-maximum (FWHM) line widths of 165 to 180 arc-sec for layers 2.5 to 3.0 μm thick, better than values for MOCVD-grown ZnSe/GaAs reported to date in the literature known to us. Cathodoluminescence (CL) imaging in the SEM showed significant defect substructure in the layers, probably due to lattice-misfit dislocations in the interface region. Bright blue CL emission from the layers was observed in the SEM at both 77K and room temperature, indicating the dominance of radiative recombination in the material.

Bulk ZnSe crystals were grown using a physical vapor transport technique. The crystals, a few millimeters on a side, had fully developed crystal facets, predominantly {110(-oriented. X-ray rocking-curve analysis gave FWHM values of about 19 arc-sec, indicating excellent structural perfection.

Growth of ZnSe on GaAs from H2S9 and Zn[N(TMS)2]2 precursors has been demonstrated. When Et2Zn is used as the zinc precursor a higher quality deposit is obtained. Results of experiments employing Et2Zn as the main zinc source with Zn[N(TMS)2]2 introduced at a dopant level indicate nitrogen has been incorporated. Final thin films were characterized by PL, XRD, SIMS, and Raman.

Among II-VI semiconductors CdTe is the one that can be grown in better crystal quality. However most of the edge and near edge luminescence properties are still to be clarified. CdTe can be obtained in both n and p type and conductivity type conversion is obtained under heat treatment.

In this work we studied the behaviour of a batch of CdTe samples under annealing in different conditions. We observed the growth and destruction of the 1.47 eV band and separated the 1.47 eV and 1.43 eV bands. We also show that these bands are strongly related with the chemical stoi chiometry.