Metallic transition metal aluminides and gallides with the CsCI structure and semi-metallic rare earth monopnictides with the NaCi structure have been grown as buried conducting layers in III-V compound semiconductor heterostructures. The criteria for achieving (100) oriented epitaxial growth on (100)111-V semiconductor surfaces is different for each class of materials. The methods used to achieve III-V/metal/llI-V heteroepitaxial structures are discussed here with emphasis on the different approaches needed for the aluminides or gallides and the monopnictides. Work producing exact lattice matching between the buried metal and surrounding semiconductor layers makes possible the separation of lattice mismatch effects from those due to other interface parameters. Results to date indicate that defect structures in the overgrown semiconductor layers arise more because of differences in crystal symmetry, interface chemistry and bonding across the interface than lattice mismatch.

Single-crystal films of InP have been deposited on GaAs, GaAs-coated Si, and InP substrates by metalorganic chemical vapor deposition (MOCVD). Defect-reduction schemes involving various thermal annealing recipes have been developed and characterized. Material quality has been assessed by a variety of methods including transmission electron microscopy, X-ray rocking curve analysis, low-temperature photoluminescence, lifetime measurements, Hall-effect measurements, electrochemical profiling, and Nomarski microscopy. The use of either a thermal-cycle-growth or a thermal-cycle-annealing process leads to heteroepitaxial InP film quality which is significantly improved over that of its as-grown state, with the thermal-cycle growth appearing to be the more effective technique.

The formation and structures of misfit dislocations are significant factors in understanding heteroepitaxy of lattice-mismatched materials. In this study, GaAs/Si, CoGa/GaAs and ErAs/GaAs heterojunctions in materials grown by molecular-beam epitaxy have been characterized using transmission electron microscopy. Different types of misfit dislocations have been generated at these interfaces. The different dislocation configurations are discussed, along with interactions between 60° and 90° dislocations in GaAs/Si heterojunctions; the 60° dislocations might be associated with surface steps or edges of islands. The growth of antiphase boundary structures in the CoGa and ErAs grown on GaAs are proposed.

The microstructure and the structure of defects in GaAs/ScxEr1–xAs/GaAs (x=0 and 0.3) heterostructures grown on (100) GaAs substrates by molecular beam epitaxy have been characterized using transmission electron microscopy. The top GaAs layer forms islands on ScxEr1–xAs at the initial growth stage, and the area covered by GaAs varies with the growth temperature. In addition to regions of epitactic (100) GaAs, regions of {122}- and (111)-oriented GaAs are observed on (100)-oriented ScxEr1–xAs. A high density of stacking-fault pyramids is found in epilayers of GaAs grown on a thin epilayer of ErAs, where the ErAs layers are only one or two monolayers thick. The apex of each stacking-fault pyramid is located at the ScxEr1–xAs/GaAs interface.

Atomic layer epitaxy(ALE) of III-V compound semiconductors is reviewed. This technology has grown in recent years because of potential applications to nanometer-order structures as well as to monolayer/cycle growth with high-uniformity in growth thickness, and to excellent selective-area growth. Recent developments in chloride ALE of various compounds and heterostructures are described. Potentials of ALE for producing such fine structures are shown.

Zinc selenide films have been grown heteroepitaxially on Si(100) substrates by molecular beam epitaxy. The growth has been carried out for raised substrate temperatures and also at room temperature followed by solid-phase epitaxial (SPE) regrowth. The ZnSe films have been characterized by a number of surface-sensitive techniques and both the interface and the bulk material have been examined with high resolution transmission electron microscopy (HRTEM). We find that an interlayer, which is most likely SiSex, is present between the ZnSe film and the Si substrate for growths made at 300 °C and causes loss of epitaxy. In the case of room temperature deposition and SPE, it is absent, leading to good epitaxy. In the latter situation, the films are very uniform and there is a 4° rotation of the ZnSe crystal axes relative to those of the Si substrate.

GaAs was grown on Si substrate by metalorganic chemical vapor deposition using GaAs/GaAsP strained layer superlattice (SLS) intermediate layers. The dislocation density decreases at the interface between GaAs and SLS, but does not decrease in the SLS. When GaAs/GaAsP SLS is used as the intermediate layer, a part of the dislocation propagates into the top GaAs layer because of the lattice mismatch of GaAs and SLS. The low etch-pit-density of (3-5) x 105 cm−2 was obtained by using the intermediate layer of GaAs/GaAsP SLS and AlAs/GaAs superlattice with thermal-cycle annealing.

The structural quality of GaAs/Si layers deposited directly at the normal growth temperatures (650°C,750°C) is compared with that of layers grown by the standard two-step growth process using Metalorganic Chemical Vapor Deposition (MOCVD). The directly grown layers are highly twinned and polycrystalline in nature whereas the two step growth process produces single crystal layers even at growth temperatures as high as 800°C. The origin of these effects is related to the initial growth of the GaAs, which is in the form of highly defective separate islands, for the case of direct growth, and connected single crystal islands for the case of two-step growth. The directly grown islands exhibit a “ripening” type behavior, with a strong dependence of the Si substrate surface coverage by the GaAs layer, on the growth temperature. The generation of structural defects such as stacking faults and microtwins, which destroy the epitaxial relationship could be triggered by the presence of surface imperfections on the Si substrate.

We have successfully grown undoped GaAs of very high resistivity on Si by MOCVD. The back and side edges of the Si substrate were coated with a Si3N4/SiO2 stacked layer to suppress Si incorporation Into GaAs by the gas phase transport mechanism during MOCVD growth. A 3- μm-thick GaAs layer was grown on this Si substrate at 750 °C in an atmospheric MOCVD reactor using the two-step growth technique. The electron concentration measured by a Polaron C-V profiler is 3xl0l4 cm−3, as low as that of GaAs grown on GaAs substrate, up to the depth of 1.5 μm from the surface.

The novel concept of using a SixGe1–x multilayer structure as a buffer layer between a silicon substrate and a GaAs epitaxial layer to accommodate the GaAs/Si 4.1% lattice mismatch is introduced. Initial results using a 340 nm trilayer SixGe1–x multilayer structure are presented and are critically assessed. Significant potential is demonstrated, and the work to date indicates that certain guidelines and procedures must be adhered to for this method of threading dislocation reduction to be effective.

The nucleation and interfacial defect structure of thin GaAs films grown on reactive ion etched Si substrates by normal molecular beam epitaxy (MBE) and modulated molecular beam epitaxy (MMBE) at 300°C were studied by plan view and high resolution cross-sectional electron microscopy (TEM). Plan view TEM micrographs show a pronounced three-dimensional (3-d) island type nucleation for the MBE grown sample. A high density of microtwins is also found in these nucleated islands from high resolution cross-sectional TEM micrographs. The 3-d nucleation and the interfacial twinning is suppressed however in the MMBE grown samples. The FWHM of the (400) Bragg peak for 3 μm thick GaAs on Si films shows a reduction of 60 arcseconds when the initial buffer layer is grown by MMBE as compared to normal MBE.

InP and GaInP layers were heteroepitaxially grown on (100) Si substrates by atmospheric pressure MOCVD. TEM and photoluminescence (PL) were used to measure the defect density and the minority carrier lifetime in these structures. The direct growth of InP on Si resulted in either polycrystalline or heavily faulted single-crystal layers. The use of GaAs buffer layers in InP/Si structures gave rise to significantly improved morphology and reduced the threading dislocation density. The best InP/Si layers in this study were obtained by using GaAs-GaInAs graded buffers. Additionally, the growth of high quality GaInP on Si was demonstrated. The minority carrier lifetime of 7 ns in these layers is the highest of any III-V/Si semiconductor measured in our laboratory.

Epitaxial InP films have been successfully deposited on GaAs coated silicon wafers with a buried oxide for the first time by MOCVD. The SOI wafers were prepared using the Separation by IMplantation of Oxygen (SIMOX) process. The quality of InP on SIMOX is comparable to the best of InP on Si deposited in the same reactor. Preliminary results on defect reduction techniques such as Thermal Cycle Growth (TCG) show an order of magnitude increase in the photoluminescence intensity and a factor of five reduction in the defect density. TCG has been found more effective than Thermal Cycle Annealing (TCA) in improving the crystalline perfection and optical properties of the deposited films.

Growth of Ge on GaAs at reasonably high temperatures, which produce better crystallinity in the Ge, presents serious difficulties due to the dissociation of the GaAs substrate. In this paper, we describe the growth of a lowtemperature buffer layer of Ge on GaAs that prevents decomposition of the GaAs during high-temperature growth of Ge. Using this approach, we present the first report of highly specular, mass-transport-limited high-temperature growth of Ge on GaAs that is comparable to the homoepitaxy of Ge. The factors affecting the minority-carrier lifetime of Ge on GaAs, using such an epitaxial growth technique, were studied with a non-invasive microwave technique. Lifetime variations, from very low values to about 0.45 μsec, were obtained as a function of the growth conditions. Significantly, the removal of the surface oxide on the GaAs substrate prior to low-temperature buffer-layer growth, terminating the flow of germane(GeH4) during the ramp to high growth temperatures, thinner buffer layers, and high-temperature growth of Ge were found to be important for obtaining long lifetimes.

Alkyl substituted arsine compounds, RnAsH3–α are attractive alternatives to arsine, AsH3. for metalorganic chemical vapor deposition (MOCVD) of GaAs-based compounds because they are typically low vapor pressure liquids which can be stored and handled more safely than the high-pressure gas cylinders used for AsH3. Despite their increased safety, the alkylarsines have not been widely used due to carbon incorporation problems and high background doping levels in the deposited films. To determine the impact of alternative growth chemistries on MOCVD processes we have investigated the thermochemistry controlling the decomposition of AsH3 and its alkyl substitutes. Data are presented on the thermal stability of the Ascompounds, their resulting growth properties, and the composition and formation kinetics of the volatile products formed during thermal decomposition in an H2 ambient. The gas phase reactions controlling decomposition are identified. The implications of our results for CVD growth models and the potential of alkylarsine compounds for different CVD processes are discussed.

Growth of (111)B oriented GaAs, GaInAs, and AlInAs by MBE was investigated through a study of surface morphology, R.HEED patterns, and photoluminescence. Considering growth on both nominally oriented and 2 ° mis-oriented (111)B GaAs substrates, we have found that MBE growth in the (111)B direction proceeds quite differently than (100) growth. Except in the case of high substrate temperature growth on nominally oriented (111)B substrates, the growth of (111)B GaAs and GaInAs results in films which are characterized by macroscopically rough or faceted surfaces and by weak photoluminescence. We demonstrate that the surface morphology of these macroscopically rough films may be dramatically improved by growing with modulated Ga and In fluxes. Also, we find that AlAs and Al-containing alloys grow much more smoothly than GaAs on the (111)B surface. We report an AlAs/Al.5In.5As strained MQW structure which exhibits both good surface morphology and good photoluminescence spectra. Growth mechanisms which may explain the observed differences between (111)B and (100) MBE growth are proposed.

The heteroepitaxial growth of InP and GaInAs on GaAs substrates has been studied by using a new combination of source materials: ethyldimethylindium (EDMIn) and trimethylgallium (TMGa) or triethylgallium (TEGa) as group III sources, and tertiarybutylphosphine (TBP) and tertiarybutylarsine (TBAs) as group V sources. The heteroepitaxial growth was carried out in a horizontal reactor in H2 under atmospheric pressure using a 2 kW quartz lamp as the substrate heater. Epitaxial InP layers of good surface morphology were obtained by using a two step process. The continuity and thickness of the buffer layer are important parameters. The InP layers deposited at 600°C are n-type, and the electron concentration decreases with decreasing TBP/EDMIn molar ratio. The 4.2 K photoluminescence of InP films is very similar to that of homoepitaxial InP films deposited at 600°C using trimethylindium (TMIn) and phosphine. Epitaxial GaxIn1–xAs layers with In composition varying from 3% to 53% have been deposltedi on GaAs substrates at 500° -550°C. A single growth step can be used for the deposition of GaxIn1–xAs with In composition of less than 20%. An InP buffer layer was used when the GaxIn1–xAS layer contains about 53% In. The composition of GaInAs was determined by optical absorption and photoluminescence techniques.

Layers of InSb and InAsxSb1-x were grown on GaAs and GaAs on Si substrates and then characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) to determine the epilayer quality. Hall-effect measurements and photoluminescence (PL) were also performed. Single-crystal XRD indicated that the 5-μm InSb layers grown on GaAs had a peak full width at half maximum (FWHM) of 120 arc sec for the (004) reflection. Planar TEM of a 7-μm-thick InSb layer on GaAs(001) indicated a dislocation density of 2 x 106 cm−2 at the top of the layer. Hall effect measurements of an undoped 3.5-μm-thick InSb on semi-insulating GaAs indicated an electron density of 3.7 x 1016 cm−3 at 300K and a mobility of 45,000 cm2 / V-sec. At 77K these values were 2.7 x 1016 cm−3 and 49,200 cm2 / V-sec, respectively. The composition of the InAsxSb1-x was a function of the growth temperature and the As2/In ratio for both Sb2 and Sb4. The XRD (004) peak FWHM increased with the x value, indicating a deterioration in material quality. This may be caused by alloy segregation in InAsxSb1-x. The peak FWHM rapidly increases from x=0.1 to x=0.3 and then its value drops, indicating that the quality of the layers improved. InSb layers displayed a strong PL whereas the PL for the InAs0.5Sb0.5 layers was very weak. We also grew InSb and InAsxSb1-x layers on GaAs on Si. Optical transmission measurements on InSb indicated that the layers were under tensile stress. We believe this tensile stress could be used to lower the bandgap of InAsxSb1-x layers to provide longer cut-off wavelengths for infrared detectors.

The MBE growth and related materials characterisation of InSb/InAlSb strained-layer structures is described. Band-gap considerations and critical thickness calculations are presented and indicate that this material system should offer considerable device potential. Detailed structural studies, performed using both transmission electron microscopy and X-ray diffraction, confirm the growth of high quality multiple quantum-wells, and 2K photoluminescence has shown corresponding energy upshifted transitions.

We have successfully grown InGaAs/AIAsSb quantum-well (QW) structures lattice-matched to InP by molecular beam epitaxy for the first time. We studied the band-edge discontinuity and the interface abruptness of these heterostructures. A cross-sectional lattice image of InGaAs/AlAsSb QWs taken along the [100] axis showed atomically smooth heterointerfaces. The photoluminescence (PL) peak energy of the 20-nm-thick InGaAs well (0.758 eV) was lower than that of InGaAs bulk (0.799 eV), indicating that the InGaAs/AlAsSb system has a staggered lineup. The conduction band-edge discontinuity, ΔEc, was evaluated to be 1.74 ± 0.04 eV, which was derived from parameter fitting to the 4.2 K PL peak energy shifts of QWs as a function of InGaAs well width between 2.1 nm and 20 nm. The corresponding valence band-edge discontinuity, ΔEv, was 0.07 ± 0.02 eV. We also fabricated a resonant tunneling barrier structure of InGaAs (4.4 nm)/AlAsSb (2.9 nm), and obtained a very high peak-to-valley current ratio of 15 at 300 K.