Ultraviolet light-driven epitaxial growth of gallium arsenide at reduced substrate temperatures

We report on the photodeposition of gallium arsenide on gallium arsenide and silicon at low substrate temperatures utilizing ultraviolet radiation. A 1000 W Hg-Xe arc lamp serves as the light source with triethylgallium and arsine serving as the reactants. In this study, single crystal gallium arsenide thin films are obtained at substrate temperatures of approximately 357°. The electrical, chemical and structural properties of the photodeposited films are presented and the mechanisms involved in the deposition process are discussed. It is found that both photolytic and pyrolytic mechanisms are involved in the deposition process for the experimental conditions considered and that the desorption of excess arsenic is important in the low temperature growth of GaAs using photochemical means.     

An analytical evaluation of GaAs grown with commercial and repurified trimethylgallium

An analytical study of the impurities in trimethylgallium (TMGa) and subsequent correlation of the effect of these impurities on resulting GaAs films grown by metalorganic chemical vapor deposition (MOCVD) is presented. The effects of using fractional distillation techniques to improve the quality of TMGa and to help isolate and identify major source impurities in TMGa is detailed. Photothermal ionization data are presented which show the residual donor species present and their relative concentrations in the epitaxial layers. Correlations of the residual donor concentrations with TMGa preparation are made. It is demonstrated that high purity GaAs with μ₇₇ K ≈ 125,000 cm²/V-sec can be grown by MOCVD using repurified trimethylgallium and arsine source materials. Work supported in part by the U.S. Naval Research Laboratory on Contract No. N00173-80-C-0066.     

Investigation of carbon incorporation in GaAs using13C-enriched trimethylarsenic and13Ch4

In the metalorganic chemical vapor deposition of GaAs there is increasing interest in replacing arsine with a less toxic arsenic source. However, GaAs films grown with metalorganic arsenic reactants usually contain significantly higher levels of carbon than films grown with arsine. Using 50% isotopically enriched¹³C trimethylarsenic (TMAs), we report the first direct evidence that the methyl groups from TMAs are a major source of the carbon observed in the GaAs films. The measured¹³C concentration in these films was 5 x 10¹⁶ cm.³ Conversely, incorporation of¹³C was not detected when 99%¹³C-enriched methane was added to the source gases during growth of GaAs with arsine in place of the¹³C-TMAs.     

Laser enhanced epitaxial growth of gallium arsenide from elemental arsenic

Metalorganic compounds and group V hydrides absorb strongly in the far ultraviolet region. The metalorganic vapor phase epitaxial (MOVPE) growth of gallium arsenide (GaAs) can be enhanced by irradiation with a laser of appropriate wavelength. To alleviate the hazard associated with arsine, the commonly used group V source for MOVPE of GaAs, elemental As has been used in this work. Elemental arsenic is believed to be the best alternate As source for most applications; organoarsenic compounds (such as tertiarybutylarsine), though of scientific interest, are unlikely to be used for epitaxial GaAs production because of their extremely high costs. The use of ArF excimer laser (193 nm) has been found to enhance the epitaxial growth of GaAs from As and triethylgallium (TEGa). The epitaxial temperature is reduced, and the growth rate is increased. The extent of enhancement depends strongly on the laser fluence. The grownfilms ] are usuallyn-type with a room temperature net carrier concentration of (1-6) x 10¹⁵ cm^-3; however, mobility measurements indicated a high degree of compensation, particularly in films grown under high fluences. Epitaxial GaAs films grown with high laser fluence have also been found to have high carbon concentration from photoluminescence measurements, due presumably to the dissociation of C-C and C-H bonds in TEGa. This type of material may not be suitable for certain minority carrier devices. Supported by SDIO/ONR under contract N00014-90-C-0032-P00003 and DARPA under grant MDA972-88-5-1006.     

Optimization of undoped gaas by low-pressure OMVPE using trimethylgallium

Optimization of the electrical characteristics of undoped GaAs grown by low-pressure OMVPE using trimethylgallium is presented. The use of a lower growth pressure was found to reduce both then- andp-type background impurity incorporation. Both electrical and optical measurements revealed that the arsine partial pressure controls the background impurity level during low-pressure growth. Variation of this parameter allowed the attainment of both high mobility (maximum of 136,000 cm²/V-sec at 77 K in this study) and high resistivity layers suitable for field-effect transistor buffers. AlGaAs/ GaAs two-dimensional electron gas structures and GaAs MESFETs using the high resistivity buffer layers showed excellent electrical characteristics. Similar trends were obtained using different AsH₃ sources despite variations in purity.     

Growth of zinc- blende GaN on GaAs (100) substrates at high temperature using low-pressure MOVPE with a Low V/lll molar ratio

Zinc-blende GaN films were grown on GaAs (100) substrates by low-pressure metalorganic vapor phase epitaxy using trimethylgallium or triethylgallium and NH₃. Films grown at lower temperatures contained considerable amounts of carbon, but the carbon concentration was reduced in high temperature growth. When the film was grown at 950°C using triethylgallium and NH₃, its carbon concentration was on the order of 10¹⁷ cm⁻³. The crystalline and optical quality of zinc-blende GaN crystal also improved with high-temperature growth at a low V/III ratio using a thin buffer layer. The films exhibited only one sharp photoluminescence peak at 3.20 eV with a full width at half maximum as low as 70 meV at room temperature.     

Growth of device quality GaAs by chemical beam epitaxy

The growth of high purity GaAS with excellent uniformity and very low defect density by chemical beam epitaxy using triethylgallium and arsine is described. The residual background impurity is mostly carbon. A mobility of 518 cm²/Vs with a hole density of 3.6 x 10¹⁴ cm⁻³ has been obtained for a growth temperature of 500° C. The electrical quality is further evaluated by fabricating a Si doped epilayer into MESFET device using 1 μm gate length. A transconductance of 177 mS/mm has been measured. The results indicate that chemical beam epitaxy is a very attractive growth technique for GaAs integrated circuits.     

Capless annealing of silicon implanted gallium arsenide

Numerous commercially available semi-insulating GaAs substrates have been implanted with silicon ions and the post implantation annealing carried out using the technique of capless annealing in an arsine atmosphere. Results are presented on the implanted atomic silicon distribution along with carrier concentration and mobility profiles, Hall mobility and percentage activation figures for various implanted substrates. The phenomenon of thermally induced surface conduction layers in semi-insulating GaAs is discussed in the context of a capless annealing technique.     

Investigations on low temperature mo-cvd growth of GaAs

The growth conditions for the deposition at low temperatures of epitaxial layers of GaAs on (100) GaAs crystals using TMG and arsine are studied in detail. The films are grown at atmospheric pressure in a vertical reactor in which the arsine is fed in through the rf heated susceptor for precracking. The growth temperature was varied between 680°C and 450°C. In the whole temperature range epitaxial growth was obtained. The growth rate at temperatures below 600°C depends on the AsH₃ flow, suggesting that the availibility of As vapor species, not AsH₃ limits epitaxial growth in this temperature range. For a constant AsH₃ /TMG ratio of 8 the growth rate decreases by exp (-E/kT) with an activation energy of E = 1.5 eV. Growth rates as low as 0.5 um/h have been achieved. Unintentionally doped layers show semi-insulating behaviour at growth temperatures below 500° C, similar to the behaviour seen from MBE layers. However, n-type layers with reasonable mobilities can be grown in the low temperature range (450 ° C) using H₂ Se as the doping gas.     

The growth of GaAs,AIGaAs, InP and InGaAs by chemical beam epitaxy using group III and V alkyls

The growth kinetics of chemical beam epitaxy (CBE) were investigated with the growth of GaAs, AIGaAs, InP, and InGaAs. Results obtained with epilayers grown by using trimethylarsine (TMAs) and triethylphosphine (TEP) instead of arsine (AsH3) and phosphine (PH₃) were reviewed with some additional results. The CBE grown epilayers have similar optical quality to those grown by molecular beam epitaxy (MBE). Superlattices of GaAs/AlGaAs with abrupt interfaces have been prepared. Since trimethylindium (TMIn) and triethylgallium (TEGa) used in the growth of InGaAs emerged as a single mixed beam, spatial composition uniformity was automatically achieved without the need of substrate rotation in the InGaAs epilayers grown. Lattice-mismatch Δα/α< 1 x 10^-3 have been reproducibly obtained. For epilayers grown with high purity TMAs source, room-temperature electron mobility as high as 9000 cm²/V sec and concentrations of ˜7 x 10¹⁵ cm^-3 were produced. In general, the electron mobilities were as good as those obtained from low-pressure metalorganic chemical vapor deposition. (MO-CVD). Unlike MBE, since the In and Ga were derived by the pyrolysis of TMIn and TEGa molecules at the heated substrate surface, respectively, oval defects observed in MBE grown epilayers due to Ga splitting from Ga melt were not present in CBE grown epilayers. This is important for integrated circuit applications. Unlike MO-CVD, the beam nature of CBE allows for selective area growth of epilayers with well-defined smooth edges using mask shadowing techniques. Typically, growth rates of 2-5μm/h for InP, 2-6μm/h for GaAs and AIGaAs, and 2-5μm/h for InGaAs were used.     

Multiplanar silicon doping of GaAs using disilane by GSMBE

Silicon multiplanar doping was employed to improve the disilane doping efficiency during the growth of GaAs by GSMBE using triethylgallium and arsine as matrix element sources. The doping efficiency was 100% for Si planar separations ( delta s) of 10 nm or greater. A maximum carrier concentration of 7.5*10/sup 18/ cm/sup -3/ was achieved at delta s=5 nm.<>     

Carbon reduction in triethylarsenic-grown GaAs films using chemically activated arsine as a co-reagent

N-type gallium arsenide films grown from triethylarsenic (Et₃As) and trimethylgallium (Me₃Ga) are generally of poor quality (μ_77K(max) = 16,100 cm²/V-s) and are severely contaminated with carbon (>10¹⁸ cm⁻³), whereas films grown using a mixture of triethylarsenic and arsine (AsH₃) with Me₃Ga are typically of high purity (β_77K(max) = 60,000 cm²/V-s) and contain significantly reduced carbon levels (~mid-10¹⁵ cm^-3). These differences in film purity are due to the inherent growth chemistry of each reagent mixture. The respective growth chemistries of these reagent systems have been inferred from a series of decomposition experiments carried out under pseudo-growth conditions, and the differences in growth chemistry are consistent with the differences in corresponding epilayer purity. Triethylarsenic appears to decompose primarily via a bond homolysis reaction to generate alkyl-containing radical species, which can react with a growing GaAs epilayer to cause severe carbon contamination. In the Et₃As/AsH₃ coreagent system, the Et₃As reagent decomposes to produce these alkyl-containing radical intermediates, but they then apparently react further with the arsine co-reagent to generate reactive arsenic hydride radicals under relatively facile conditions. These reactive arsenic-hydride radical species can contribute to the GaAs growth process without introducing carbon into the resultant films.     

Intentional ρ-type doping by carbon in metalorganic MBE of GaAs

We report on the intentional ρ-type doping of GaAs layers grown in an UHV system from molecular beams of arsine (AsH₃) and mixtures of frimethyl gallium (TMG) and friethyl gallium (TEG). The entire doping range between 10¹⁴ cm^-3 (growth from pure TEG) and 10²⁰ cm^-3 (growth from pure TMG) can be covered by using mixtures of TMG and TEG. As revealed by SIMS and photoluminescence (PL) carbon is the dominant acceptor in the layers. Comparison of the Hall mobility and of the PL spectra shows that the quality of our films equals that of the best LPE and MBE grown ρ-type GaAs layers.     

Growth of AlxGa1−x as by metalorganic chemical vapor deposition using trimethylgallium and trimethylamine alane

High-quality Al_xGa_1−xAs layers with aluminum arsenide contentx up to 0.34 have been grown in a low pressure metalorganic chemical vapor deposition (MOCVD) system using trimethylgallium (TMG), trimethylamine alane (TMAA) and arsine. The carbon content in these films depended on growth conditions but was in general lower than in those obtained with trimethylaluminum (TMA) instead of TMAA in the same reactor under similar conditions. Unlike TMA grown layers, the TMAA grown Al_xGa_1−xAs layers, (grown at much lower temperature—down to 650° C), exhibited room temperature photolu-minescence (PL). Low temperature (25 K) PL from these films showed sharp bound exciton peaks with a line width of 5.1 meV for Al_0.25Ga_0.75As. A 39 period Al_0.28Ga_0.72As (5.5 nm)/GaAs (8.0 nm) superlattice grown at 650° C showed a strong PL peak at 25 K with a line width of 5.5 meV attesting to the high quality of these layers.     

Atomic force microscopy studies of CdTe films grown by epitaxial lateral overgrowth

Epitaxial lateral overgrowth (ELO) of CdTe was carried out on GaAs using silicon nitride as the mask material. Windows were delineated on silicon, nitride mask deposited on GaAs substrates and CdTe was grown using metalorganic vapor phase epitaxy. The films were characterized by atomic force microscopy (AFM). It has been shown that highly selective growth of CdTe can be achieved at temperatures higher than 500 C and pressures lower than 25 torr using silicon nitride as the mask layer. Optimizing the growth conditions as well as the stripe directions on the substrates enables the growth of ELO-CdTe with a flattop surface and vertical sidewalls. AFM studies show that ELO-grown CdTe contains large grains with reduced defect densities, but there seems to be no difference on the films grown on the window region or on the masked region. The results suggest that the growth mechanism for CdTe growth on GaAs is different from that of ELO-grown GaN. A possible growth model for the patterned CdTe growth is also proposed.     

Hot plasma chemical vapor deposition of GaN on GaAs(100) substrate

GaN films have been deposited on GaAs(lOO) substrates by a novel growth technique, hot plasma chemical vapor deposition. A radio frequency N plasma source with high power, up to 5 kW, provides an abundance of nitrogen atoms during growth. In addition, strong ultraviolet emissions from the hot plasma irradiate onto the substrate and promote the dissociation of triethylgallium, this results in growth of GaN at very low temperature (even at room temperature). In this paper, we describe the characteristics of hot nitrogen plasma and present the results of the low temperature growth of GaN. In addition, we have investigated the effects of the nitridation of GaAs substrates. Reflection high energy electron diffraction indicates the formation of a surface cubic nitrided layer on the pretreated GaAs. The GaN films grown on fully nitrided GaAs(l00) substrates are of dominantly cubic structures.     

A comparison of TMG with TEG for the growth of InxGa1−xAs

MOCVD growth of In_xGa_1?xAs from trimethylgallium (TMG), triethylgallium (TEG), trimethylindium (TMI) and arsine was studied over a wide range of growth conditions. It was found that the In_xGa_1?xAs strain with respect to InP is strongly influenced by the arsine concentration when grown with TEG and TMI. In contrast the In_xGa_1?xAs strain was independent of arsine concentration when grown with TMG and TMI. It was also observed that the growth rate of In_xGa_1?xAs is higher for TMG than for TEG with the same TMI and arsine flow. In addition an interaction between TEG and dimethylzinc (DMZ) was also observed. We show that MOCVD growth process involves many complex reactions and cannot be considered as a simple decomposition of each precursor. The interactions between precursors, which takes place in the gas phase or on the growing surface, has to be considered. We have utilized the TEG/arsine interaction for the growth of strain compensated superlattices by modulating the arsine flow into the reactor chamber while keeping the TEG and TMI constant. Structures with up to 100 periods of 100 Å of +1% In_0.6Ga_0.4As and 200 Å of ?0.5% In_0.5Ga_0.5As were grown with excellent characteristics.     

Photoluminescence spectroscopy measurement of elastic strain in heteroepitaxial GaAs films

GaAs films have been grown on silicon and various insulating substrates. These include silicon-on-sapphire, silicon with a buried implanted oxide, and single crystal sapphire. Quantitative comparison of the respective measured shifts in the dominant photoluminescence peaks (7 K) indicates that the GaAs layers deposited on silicon-on-sapphire substrates that have been microstructurally upgraded by the double solid-phase epitaxy process are strain-free.<>     

Molecular-beam epitaxy of mercury-cadmium-telluride solid solutions on alternative substrates

Growth processes were considered for heteroepitaxial structures based on a mercury-cadmium-telluride (MCT) solid solution deposited on GaAs and Si alternative substrates by molecular-beam epitaxy. Physical and chemical processes of growth and defect-generation mechanisms were studied for CdZnTe epitaxy on atomically clean singular and vicinal surfaces of gallium-arsenide substrates and CdHgTe films on CdZnTe/GaAs surfaces. ZnTe single-crystalline films were grown on silicon substrates. Methods for reducing the content of defects in CdZnTe/GaAs and CdHgTe films were developed. Equipment for molecular-beam epitaxy was designed for growing the heteroepitaxial structures on large-diameter substrates with a highly uniform composition over the area and their control in situ. Heteroepitaxial MCT layers with excellent electrical parameters were grown on GaAs by molecular-beam epitaxy.     

The growth and properties of mixed group V nitrides

Bearing in mind the problems of finding a lattice-matched substrate for the growth of binary group III nitride films and the detrimental effect of the large activation energy associated with acceptors in GaN, we propose the study of the alloy system AlGaAsN. We predict that it may be possible to obtain a direct gap alloy, with a band gap as wide as 2.8eV, which is lattice-matched to silicon substrates. The paper reports our attempts to grow GaAsN alloy films by molecular beam epitaxy on either GaAs or GaP substrates, using a radio frequency plasma source to supply active nitrogen. Auger electron spectra demonstrate that it is possible to incorporate several tens of percent of nitrogen into GaAs films, though x-ray diffraction measurements show that such films contain mixed binary phases rather than true alloys. An interesting observation concerns the fact that it is possible to control the crystal structure of GaN films by the application of an As flux during growth. In films grown at 620°C a high As flux tends to increase the proportion of cubic GaN while also resulting in the incorporation of GaAs. Films grown at 700°C show no evidence for GaAs incorporation; at this temperature, it is possible to grow either purely cubic or purely hexagonal GaN depending on the presence or absence of the As beam.