Highly sterically hindered chalcogenolato complexes M(EC6H2R3-2,4,6)2 (M = Zn, Cd, Hg; E = S, Se, Te; R = Me, Pri, But) have been prepared. Compounds with R -= But are volatile under reduced pressure and are suitable as precursors for the deposition of II-VI films.

This paper discusses the application of gas chromatography-mass spectroscopy (GC-MS) to the assessment of precursors for the MOVPE growth of (Hg,Cd)Te. GC-MS has been used to analyse precursors for volatile organic and organometallic impurities. An extension of the technique has also allowed precursor decomposition reactions and interactions to be studied. Information obtained on alkyl purity, decomposition and interactions has been shown to be of direct relevance to the optimisation of growth.

We report the utility of \Cd(Se4)2]2-, \Cu4Se12]2- and \In3Se15]3- as convenient low temperature precursors to semiconducting CdSe and CuInSe2. DMF and DMSO solutions of these complexes react with Se-abstracting reagents such as CN- and n-(Bu3)P to yield the corresponding binary solids at 155 °C or less. Appropriate stoichiometric mixtures of \Cu4Se12]2- and \In3Se15]3- react to give CuInSe2. The semiconducting solids were characterized with UV/vis spectroscopic, X-ray crystallographic and electron (scanning and transmission) microscopic techniques. The particle size of these materials can range from the quantum-size regime to the bulk regime, depending on the reaction conditions, metal precursor complex and Se-abstracting reagent used.

The unintentional and intentional incorporation of carbon has been investigated in order to understand both the growth kinetics as well as develop new and useful carbon doping sources. We present in this study a systematic investigation of the use of halomethanes during the MOVPE based growth of GaAs. We have used 13C tagged trimethyl gallium, AsH3, together with non-isotopically tagged halomethane sources, in order to determine the source and mechanism of the carbon incorporation. The carbon concentration was determined by secondary ion mass spectroscopy (SIMS). The carbon incorporation in the unintentionally doped material is compared to that obtained with the series of halomethanes, CHxI4-x (x=0,2-4), the chlorine analogs, CHC13 and CCI4, and the bromine containing compounds, CHBr3 and CBr4 which are used to intentionally introduce carbon in the epitaxial GaAs. The incorporation of carbon is studied here as a function of the halogen/H ratio in the source material and on the halogen ligand on the carbon nucleus. The standard growth parameters of susceptor temperature and gas phase composition were varied in order to discern the useful growth parameter regimes for these compounds.

High levels (≃ 1018cm-3) of oxygen were introduced into GaAs by using dimethyl aluminum methoxide (DMAlM0) as an oxygen-bearing precursor during metalorganic vapor phase epitaxy. Layers co-doped with oxygen and intentionally added silicon, both to concentrations of ≃ 1018 cm-3, were depleted of free carriers and had no measurable luminescence. Deep levels were present in layers grown with lower oxygen incorporation, but the compensation mechanism due to oxygen incorporation is not apparently tied to a specific defect level. The material with the electronic deep levels also possessed deep luminescence energy lines. All layers exhibited excellent surface morphology. For comparison, other layers were grown by introducing low levels of 02 and trimethyl aluminum during GaAs growth. The surface morphology of these layers was usually hazy and the layers did not exhibit the same well defined electrical and optical characteristics as the layers grown with DMAlMO.

Trimethylamine alane (TMAAl) has been demonstrated to be a superior Al precursor for growth of AIGaAs by metal-organic molecular beam (MOMBE). TMAA1 reduces both carbon and oxygen contamination relative to the standard Al source, triethylaluminum (TEA1). However, AlGaAs grown with TMAAl still shows a residual oxygen background of ∼2 × 1018 cm−3 when used with triethylgallium (TEGa) and either As4 or ASH3. This background is independent of Al mole fraction and is due primarily to alkoxides in the TEGa. AIGaAs grown with TMAAl and elemental Ga contains oxygen at levels commonly obtained in MBE, −2 × 1017 cm-3. While an oxygen level of −2 × 1018 cm-3 is not desirable, we have found that most of this impurity is electrically inactive as evidenced by room temperature photoluminescence and n-type dopant activation. In light of this, we have assessed the applicability of AlGaAs grown with TMAAl to the fabrication of high-speed GaAs/AIGaAs devices. The source is found to be suitable for structures like the heterojunction bipolar transistor.

We have investigated the growth of Alx Gal-xAs (0.1 ≤ x ≤ 1) by organometallic vapor phase epitaxy using trimethylamine alane (TMAA1) as the aluminum precursor. A low pressure (30 Torr) reactor was used with hydrogen as the carrier gas. At the high gas velocities (> 1 m · s-1) employed there was no visible deposition upstream of the substrate. AIGaAs epilayers with featureless surface morphology could be obtained over the entire range of composition. The layers exhibited very strong room-temperature photoluminescence and excellent compositional uniformity (x = 0.235 ± 0.002 over a 40 mm diameter). A comparison was made between the electrical and optical characteristics of AlGaAs grown with either trimethylgallium (TMGa) or triethylgallium (TEGa). The hole concentration of the layers grown using TMGa was significantly higher than that with TEGa (e.g., 6–7 × 1017 cm-3 vs. 1 × 1016 cm-3) for the same TMAA1 and AsH3 mole fractions. High-purity AlGaAs was achieved with TMAAl and TEGa at higher AsH3 flow rates.

Films of GaN have been grown on silicon by remote plasma-enhanced chemical-vapor deposition using trimethyl gallium and ammonia. The ammonia is rf plasma excited along with He, and the trimethyl gallium is introduced downstream from the plasma generation zone. The activation energy for the growth of GaN is 0.95±0.05 eV. This is tentatively assigned to the activation of NH groups, extracted from the plasma as primary precursors for the surface reaction with trimethyl gallium (TMG), or adsorbed fragments of this molecule. At high He flow rates, an abrupt increase in the growth rate is observed corresponding to a change in the reaction mechanism which is attributed to the formation of atomic nitrogen.

Doping of indium phosphide, grown by organometallic vapor phase epitaxy (OMVPE), has been carried out using hydrogen sulfide. For low partial pressures of H2S, the carrier concentration in the epitaxial layers is found to increase linearly. However, for higher partial pressures a region of superlinear doping is seen. For still higher partial pressures, a rapid decrease in carrier concentration is seen. In the linear region, the doping has a weak dependence on phosphine pressure, however, peak carrier concentration is higher for lower phosphine pressures.

The layers were studied using Hall Effect and Double Crystal X-Ray Diffraction, in order to elucidate the nature of impurities and compensating centers introduced. A model which explains the above characteristics is proposed for S incorporation in MOVPE grown InP.

We present an analysis of compositional variations in the growth of the compound semiconductor, InxGal-xAs, by metal organic chemical vapor deposition (MOCVD). A three dimensional transport model for fluid flow, heat, and mass transfer is solved using the finite element method. The Delta Lattice Parameter (DLP) model is used to describe the thermodynamics of the solid solution, and the Hertz-Langmuir equation is used to calculate the evaporation rate of indium from the growing crystal. Wall depletion is incorporated by allowing for explicit wall deposition of In vapor throughout the reactor.

Comparison of model predictions with experimental observations by MOCVD of InGaAs in a horizontal reactor suggests that transport phenomena lead to composition variations across the substrate, and that solution thermodynamics have little effect on the InAs incorporation rate at a given deposition temperature. However, thermodynamic factors appear to influence the change in indium incorporation with growth temperature.

A novel, close-spaced, inverted, stagnation flow, organometallic vapor phase epitaxy (OMVPE) reactor has been designed and fabricated for achieving high deposition efficiency and good large-area uniformity for solar cell applications. A computer model for this reactor, which is based on the conservation of mass, momentum, energy and species equations, has been used for predicting its operating characteristics. Due to the close spacing between the nozzle and susceptor, extensive measurements of the nozzle temperature were carried out for different reactor conditions and compared with simulation results. The maximum nozzle temperature was about 110°C showing the feasibility of GaAs growth from trimethylgallium and arsine. GaAs epitaxial layers were grown at different susceptor-nozzle distances, gas flow rates, reactor pressures and susceptor temperatures. The morphology, electrical properties and thickness uniformity of the layers were found to be of an acceptable quality. The measured and computed deposition efficiencies were found to be independent of reactor pressure and increasing with decreasing gas flow rates. The highest gallium deposition efficiency achieved was about 42%.

We present detailed chemical reaction mechanisms that describe the deposition of GaAs films from tertiary-butyl-arsine (TBA) and trimethyl-gallium (TMG) as well as the deposition of AlxGa1-xAs (0≤x≤1) films from trimethyl-aluminum (TMAl), TMG and arsine during metalorganic vapor phase epitaxy (MOVPE). The kinetic models include both gas-phase and surface reactions, whose rates are used to predict production or consumption of the participating species as well as the growth rate of the film. Two-dimensional simulations of flow, heat and mass transfer in horizontal MOVPE reactors have been coupled with the kinetic models to provide a realistic picture of the process. The predicted growth rates at different operating conditions as well as the predicted incorporation ratio, x, of Al in the AlxGal-xAs films are in good agreement with experimental observations.

Contact metallizations for space-based GaAs solar cells must survive at high temperatures for several minutes. Which metallizations will survive can be predicted by properly calculated phase diagrams instead of performing hundreds of reactions. A method for calculating the ternary temperature constitution phase diagrams Is briefly explained and the phase diagrams are calculated for two Ga-As-X alloy systems. The free energy functions of the liquid and solid phases are approximated by the regular solution theory. The phase diagrams of the three binary alloy systems which form the boundaries of the ternary alloy system are utilized to calculate the binary regular solution parameters. The free energy functions for the ternary liquid and solid phases are expressed In terms of the binary regular solution parameters. The temperature and composition of the liquidus and solidus boundaries for the ternary alloy systems are calculated from these free energy functions. Calculated results are presented for the Ga-As-Ag and the Ga-As-Ge systems.

The solid phase equilibria in the Ni-In-P system at 800 °C have been determined at ambient pressure using X-ray diffraction supplemented with differential thermal analysis from room temperature to 800 °C. One ternary phase, Ni21In2P6, was found in the system. It crystallizes with space group Fm3m and is isostructural with Cr23C6. Indium phosphide forms equilibria with the nickel phosphides Ni2P, Ni5P4, NiP2 and NiP3 and indium with Ni12P5 and Ni2P. The results are in agreement with previous observations that Ni2P is a stable phase when a nickel thin film deposited on InP is reacted to completion.

The kinetics of the bromine-methanol etching of CdTe were studied in a rotating disk reactor as a function of temperature, bromine concentration, substrate orientation, and rotation rate. The results indicated that the etching process is mass transfer controlled from -20°C to 40°C and to a maximum rotation rate of 1200 RPM. A one-dimensional transport model was used to obtain effective diffusion coefficients for bromine in methanol. The diffusion coefficient of the etchant in methanol is given by 3.7×10-8 (T/η) cm2/s over the range of 2.5°C to 23°C.

A study of the changes in surface structure and composition of CdTe(100) irradiated by 248 nm excimer laser radiation in the fluence range 18-75 mJ/cm2 is presented. Material is removed from the CdTe surface at all fluences, but above a threshold fluence of 40 mJ/cm2 the surface becomes Te-rich. Reflection high energy electron diffraction measurements indicate that the original 2×1 surface reconstruction is converted to a 1×1 pattern at fluences < 40 mJ/cm2. At exposures which generate a Te-rich surface a RHEED pattern is not observed. Temperature programmed desorption experiments show that weakly bound Tex exists on the surface after exposure at all fluences used in this study. A correlation of Auger data, desorption lineshapes, and model calculations suggest that the excess Te forms three dimensional islands on the surface.

Reaction processes leading to the deposition of Si and Ge epilayers have been delineated using a combination of surface spectroscopies. The dissociative adsorption of disilane and digermane has been investigated on the Ge(111) surface using multiple internal reflection infrared spectroscopy (MIRIRS). Molecular adsorption of Si2H6 and Ge2H6 occurs for adsorption below 150K. Molecular and dissociative adsorption are competitive processes at 110-140K. Dissociative adsorption of Si2H6 and Ge2H6 occurs above 150K. Trihydride formation (SiH3 and GeH3) is favored near 150-200K, while Si-H and Ge-H bond scission becomes significant above 200K. Di- and trihydrides are dominant below 300K, while the monohydrides are most prevalent above 300K. Decomposition of all surface hydrides occurs by 600K. On the Si(100) surface, digermane adsorption leads to the deposition of a Ge overlayer. Hydrogen desorption from the Ge/Si(100) surface is strongly altered with respect to the clean Si surface. The observed desorption behavior has important consequence on the low temperature deposition of Sil-xGex by thermal CVD.

Crystalline films of Ge have been homoepitaxially grown through a liquid Au medium by the so-called vapor-liquid-solid (VLS) mechanism at relatively low temperature (400-450 °C). During the process, the Ge vapor is delivered by a molecular beam evaporator and the liquid phase in the system is formed at the interface by heating a Au metal film above its eutectic point with the semiconductor. This process has a potential of a high growth rate at low temperature. The growth process and the crystallinity of the films were monitored in situ by high energy ion backscattering and channeling. The surface morphology and quality of the films were examined by scanning electron microscopy and cross-sectional transmission electron microscopy. The experimental results are presented, together with a discussion of the growth mechanism and the nature of the liquid metal-semiconductor interface.

Low temperature and high growth rate selective epitaxial growth (SEG) on Si02 patterned Si (001) substrate in gas-source molecular-beam epitaxy (GS-MBE) using pure Si2H6 has been investigated by RHEED observation. In the temperature range of 550 to 850°C, SEG was completely obtained at an initial growth stage. Limiting conditions of SEG were closely related with critical volume of supply gas that was equal to the total amount molecules supplied on SiO2 surface during the incubation period of initial growth. The surface SiO2 was induced to evaporate with Si2H6 supplied above 800°C, so that thermal cleaning temperature for removing native oxide came down to 800°C. As a result, the maximum process temperature of Si SEG now became 800°C, and its growth rate reached as high as 645A/min at growth temperature of 700°C.

We have succeeded in depositing both activated n- and p-type μc-Si, by a low temperature, 250°C, remote PECVD process in which dopant gases (PH3 or B2H6)/Silane (SiH4) mixtures are injected downstream from the exit port of a He/H2 plasma. The room temperature conductivities and activation energies for the n- and p-type μc-Si are respectively, 40 S/cm with Eaa=0.018 eV, and 5 S/cm with Ea =0.040 eV. Doped μc-Si is obtained for PH3/SiH4 ratios up to 1%, and for B2H6/SiH4 ratios to 0.1%. For B2H6/SiH4 ratios < 0.1%, the deposited p-type material is doped a-Si rather than doped μc-Si. We have shown that these heavily doped μc-Si film are a viable candidate for the gate electrode in MOS devices. The application of these doped μc-Si films in p-i-n diode devices has also been studied.