A modulation doped Al.35Ga.65As/GaAs single interface structure using Si delta doping setback from the two dimensional electron gas (2 DEG) by 700Å, was measured in van der Pauw geometry at 0.35K and showed an electron mobility of 1.17× 107 cm2 /V see at a carrier density of 2.2× 1011electrons/cm2. An Al.30Ga.70As/GaAs single quantum-well 250Å wide of similar structure with a 500Å setback yielded a 2 DEG mobility of 5.1× 106 cm2 /Vsec at 3.0×1011 electrons/cm2under similar measurement conditions. These mobilities exceed those previously published by more than a factor of two for the single interface structure, and by nearly an order of magnitude for the quantum-well. The samples were grown by solid source MBE in a Varian Gen II modified with He closed-cycle cryogenic vacuum pumping, and in other ways, to achieve a base pressure of 1.5× 10−12 torr, as measured on a extractor-type ionization gauge that is not subject to the usual x-ray limited reading.

RHEED intensity oscillations were used to investigate As-controlled incorporation rates. The measurements were made under Ga accumulation at the surface of the substrate, and at fluxes and substrate temperatures common for 1.0 micron/hr GaAs growth. The results between the dimer and tetramer As species were compared. The transition between Ga and As controlled incorporation rates was constant within 2.5°C for a constant As flux and was independent of the substrate temperature. Also, the As-controlled incorporation rate curves shows two regions as the substrate temperature increases. At low substrate temperatures, the As incorporation rate is substrate temperature independent. Then at higher substrate temperatures, the As incorporation rate has an arrhenius dependence with a positive activation energy. An interpretation of these results is possible by assigning the maximum sticking coefficient of the tetramer to the region where the As incorporation rate is independent of substrate temperature. This assignment allows one to derive the As (dimers and tetramers) sticking coefficient dependence with substrate temperature. The dimer sticking coefficients are greater that the tetramer sticking coefficients for a given substrate temperature and As flux, and the maximum sticking coefficient of the As dimer was determined to be 0.8 in these experiments.

Optical absorption and photoluminescence experiments are performed on GaAs doping superlattices, which have a δ-function-like doping profile of alternating n-type and p-type dopant sheets. Absorption and emission spectra reveal for the first time the clear signature of quantum-confined interband transitions. The peaks of the experimental absorption and luminescence spectra are assigned to calculated energies of quantum-confined transitions with very good agreement. It is shown that the employment of the δ-doping technique results in improved optical properties of doping superlattices.

We have examined some aspects of inter-facet migration during molecular beam epitaxical(MBE) growth of AlxGal-xAs on patterned GaAs (100) substrates. Scanning and cross-sectional transmission electron microscopy are employed to examine the evolution of the growth front profile. We observe significant inter facet migration from (3111/1411) facets which originate from the terrace edges to the flat terrace region. The migration length of cations on these facets is at least 0.9 μm for GaAs growth while for A10.5Ga0.5As it is less than 0.3 μm. We also observe a decreasing inter- facet migration rate with increasing growth. This interfacet migration is exploited for in situ, growth kinetics controlled, creation of laterally confined quantum well structures on the top terrace region and photoluminescence results for these structures are presented.

We report very small interdiffusion and surface segregation of Si in δ-doped GaAs, A10.3Gao.7As and Quantum Wells grown at 580 C by Gas Source Molecular Beam Epitaxy. Capacitance-Voltage profiles of δ-doped layers are 38 Å wide for growth at 580 C and further, insignificant profile narrowing is observed at 530C and below. Much wider profiles are observed at equivalent substrate temperature for As4 growth. Atomic diffusion of Si in δ-doped Al0.3Ga0.7As is found to have a rate of D0=5× 10−cm2/sec with an activation energy of 1.8 eV.

We demonstrate a vacuum lithography process which uses a finely focused Ga ion beam to write the pattern which is then transferred to the InP pattern by low energy dry etching. Surface steps on the order of 1000-2000A in height, and lateral resolution limited only by size of the ion beam, can be efficiently prepared using moderate Ga ion fluences. The surfaces prepared by this process are damage free and suitable for epitaxial overgrowth. GaInAs/InP heterostructures grown on in-situ patterned substrates show excellent morphology and high luminescence efficiency.

Recent efforts employing reflection high energy electron diffiaction measurements to study the chemical beam epitaxial growth of GaAs is reviewed. A reaction model which assumes the dominance of Ga alkyls and their derivatives adsorbed on the growing surface can explain most of the growth results in a consistent way. Dynamic evolution of the reconstruction pattern of the adsorbed triethylgallium or trimethylgallium overlayer illustrates how the alkyl-Ga bonds are cleaved sequentially. The growth rate dependence on temperature and incident flux can be fitted quite well in this reaction model. In the absence of As flux, the existence of a metastable Ga alkyl overlayer makes possible the atomic layer epitaxy of GaAs.

In this paper, the effect of atomic hydrogen on carbon impurity incorporation during the metalorganic-molecular-beam-epitaxy (MOMBE) growth of GaAs is studied. Atomic hydrogen was introduced into the MOMBE chamber during the growth by cracking molecular hydrogen with a high temperature cracker cell. Atomic hydrogen appears to be effective in reducing the background doping level of MOMBE-grown GaAs, presumably by reacting with hydrocarbon radicals. Background doping levels as low as 4 × 1014 cm−3 and room temperature hole mobilities as high as 430 cm2/V-sec were achieved. This result demonstrates that it is feasible to grow high quality GaAs films in MOMBE without using AsH3 or a high flux of As4by introducing atomic hydrogen into the chamber during the growth.

We have grown high quality AlGaAs/GaAs heterostructures by GSMBE, using triethylalkyls and arsine, for MODFET device applications. Al.28Ga.72As/GaAs modulation-doped structures with moblilities as high as 7,200 and 47,000 cm2/V-s at 300 and 77K, respectively, were obtained for a spacer layer thickness of 30Å and a sheet carrier concentration of l×l012cm−2. These results are comparable to films of a similar structure grown by elemental source MBE or by OMVPE techniques. Quarter-micron gate length MODFETs fabricated from this material have fr greater than 38 GHz and exhibit a 1.7 dB noise figure with 10 dB associated gain at 18 GHz when operated at room temperature.

InP based alloy epitaxial heterostructures currently are being developed as light sources and detectors for optoelectronic applications. High performance requirements at very high frequency operation have resulted in the need for complex device structures which can require one or more epitaxial steps. As a result, hybrid growth techniques combining LPE with either hydride VPE, trichloride VPE or metal organic CVD previously have been used to grow emitter and photodetector heterostructures. In this paper, a hybrid trichloride-hydride VPE growth technique for complex heterostructures is described. Trichloride VPE which is particularly suited for certain regrowth applications because of its inherent in-situ etching capability has been successfully utilized to regrow low-doped, high purity InP on InP/InGaAs/InGaAsP heterostructures grown by hydride VPE. Transmission electron microscopy has shown that the regrowth interface is free of major defects and dislocations. P-diffused APD mesa devices obtained from these structures were operated with fields at the regrowth interface as high as 3.8 × 105V/cm. Primary dark currents were observed as low as 1.4nA.

Long wavelength (l.3pm<X<l.551un) InGaAs/InP multiquantum well (MQW) PIN structures in which the quantum confined Stark effect can be observed, are of particular interest because of their potential for high modulation contrast ratios and high speed operation. The chemistry of trichloride VPE lends itself to the growth of high purity InGaAsP heterostructures which are essential for the realization of high performance optical modulators and switches. In this study, we investigate the application of multi-frit trichloride VPE for the highly uniform epitaxial growth of InGaAs/InP MQW structures on two-inch InP substrates for advanced photonic device applications. The growth of MQW structures with various well thicknesses was studied as was the effect of substrate orientation. The structures have been characterized by infrared absorption and photoluminescence spectroscopy, cross-sectional transmission electron microscopy and double crystal x-ray diffraction.

The Vapor Levitation Epitaxy (VLE) system utilizes quartz frits directly in front of the growth surface of the substrate. This impacts on both epitaxial layer thickness uniformity and compositional uniformity. The highly uniform layers achievable with the process have been described.

In this paper we discuss the compositional uniformity of InGaAs epitaxial layers grown by the VLE process. The composition of the InGaAs is shown to vary with time during a growth run and across the wafer when using the same growth conditions as for an open tube halide system. This compositional variation occurs for InGaAs layers exceeding 1.5 μm in thickness. We show that with the proper gas phase composition, InGaAs epitaxial layers in excess of 5.0 μm thick can be grown with excellent compositional uniformity.

Using a real-time surface probe with 0.01 monolayer (ML) sensitivity, we determine the rate-limiting steps for atmospheric-pressure, alternating-layer-epitaxy OMCVD growth on (001) and (110) GaAs with trimethylgallium and arsine sources. The reaction of TMG with AsH3- saturated (001) GaAs is limited by a competition between decomposition (at 39 kcal/mole) and desorption of TMG chemisorbed (at −26 kcal/mole) via an excluded-volume mechanism. The reaction of AsH3with TMG-saturated (001) GaAs shows an initial fast transient followed by a slower recovery. On (110) GaAs, TMG reacts essentially instantaneously with an AsH3-saturated surface while the reaction of AsH3 with a TMG-saturated surface is relatively slow. In the latter case temperature and pressure dependences indicate a fast AsH3 -surface reaction that is blocked by an adsorbed species that must be desorbed before the AsH3 -surface reaction can take place.

A kinetic model for metalorganic vapor phase epitaxy (MOVPE) of GaAs from trimethylgallium and arsine is imbedded into two-dimensional transport phenomena descriptions of horizontal and vertical MOVPE reactors. The mechanism involves 15 gas-phase species, 17 gas-phase reactions, 9 surface species and 26 surface reactions. The surface reactions take into account different crystallographic orientations of the GaAs substrate. Carbon incorporation is predicted to occur via carbene containing species. A sensitivity analysis shows that only a few reactions are needed to simulate observed growth rates while the full mechanism is important in computing carbon levels in GaAs. The model predictions are in good agreement with data for trimethylgallium decomposition in hot isothermal tubes, with GaAs growth in horizontal reactors, and with carbon incorporation in vertical reactors. The transport-reaction model demonstrates that both gas-phase and surface reactions as well as transport phenomena are important in predicting MOVPE reactor performance.

This paper presents a detailed mathematical model of the coupled gas-phase chem- istry, surface chemistry, and fluid mechanics in the MOCVD of GaAs from trimethylgallium and arsine in a rotating-disk reactor. The model predicts steady-state deposition rates as a function of susceptor temperature and partial pressure of the reactants. Rate constants in the model have been adjusted to match experimental deposition rates from the literature.

The electrical and photoluminescent properties of vanadium incorporated into GaAs epitaxial layers from a VO(OC2 H5)3 source during organometallic vapor phase epitaxy were examined. The vanadium concentration in the GaAs was controllably varied from 1016 to 1018 atoms cm−3. Deep level transient spectroscopy showed the presence of an electron trap at Ec – 0.15 eV which increased in concentration with vanadium content of the epitaxial layers. A maximum value of 8 × 1015 cm−3 for this trap was obtained. There were no midgap electron traps associated with vanadium. In intentionally Si-doped epitaxial layers, co-doping with vanadium was observed to have no effect in reducing the carrier density when the Si concentration was > 4 × 1016 cm−3. The net carrier concentration profiles resulting from 29 si implantation into GaAs containing 1018 cm−3of total V had sharper tails than for similar implantation into undoped material, indicating the presence of less than 1016 cm−3V-related acceptors. Photoluminescent spectra exhibited the characteristic V+3intracenter emission at 0.65∼0.75 eV. No other deep level photoluminescence was detected. For a V concentration of 1016 cm−3only 2.5 × 1013 cm−3was electrically active. Over the entire V concentration investigated this impurity was predominantly (≥99%) inactive.

The crystal habits of GaAs and GaAlAs grown on structured substrates by Metalorganic Chemical Vapor Deposition (MOCVD) have been investigated. The growth behavior was delineated by depositing alternating thin layers of AlGaAs and GaAs over grooves and mesas. A strong temperature dependence of facet growth rate and an anisotropy of Al composition with facet orientation are observed. This latter effect so far undocumented in MOCVD has been analysed by Auger Electron Spectroscopy performed on cleaved cross-sections. BCF theory has been used to extract quantitative microscopic data. These observations demonstrate the importance of surface effects and provide an insight into MOCVD growth mechanisms.

The complete requested range of epitaxial deposition from one monolayer to tens of microns is available integrating LP-MOVPE and LP-VPE into wafer fabrication. Uniformity across 2 inch wafers for thickness, composition, and doping show a variation of less than 2 %. Electrical properties of the 1014 cm−3range and less for background doping, carrier mobilities of 210,000 cm2/Vs for AIGaAs and 190,000 cm2/Vs for GalnAs, both HEMT structures, are achieved. FWHM of 3.4 meV and 18.6 meV for 10 nm and 2 nm GaInAsP wells have been measured. GaAsP layers including a “graded” layer reveal FWHM of 15 nm. A new model for the understanding of high growth rates in the hydride system is demonstrated.

Flow modulation techniques have been used to prepare highly strained InAsxPl-x/InP quantum well structures in an atmospheric pressure organometallic vapor phase epitaxial reactor. The compositions of the pseudomorphic wells ranged from x=0.40 to 0.74, corresponding to biaxial compressive strains of 1.3-2.4%. Well thicknesses ranged from 2 to 26 monolayers. The flow modulation growth conditions were found to have a strong influence on interface formation in the wells. For wells grown under optimized modulation conditions, low-temperature photoluminescence spectra revealed peak-splitting of the emission from the thinnest wells. This splitting is attributed to emission from regions in the wells with atomically smooth interfaces over areas greater in lateral extent than the exciton diameter. The full-width at half-maximum of the peaks is in the 6-15 meV range, comparable to the best reported values for lattice- matched InGaAs(P)/InP quantum wells grown by any technique, and is independent of well thickness or composition.

As the demands for InP epitaxial materials grow, the need for larger throughput growth techniques becomes important. However, uniformity of thickness and particularly composition of InGaAs and InGaAsP films has proved troublesome. This has limited much of the InGaAsP growth work to single wafer machines. The purpose of this work is to demonstrate good film properties and uniformity on a multi-wafer machine that holds three, two-inch diameter wafers.