J. K. Klingert

Use of tertiarybutylarsine in the metalorganic chemical vapor deposition growth of GaAs

Epitaxial films of GaAs have been grown by metalorganic chemical vapor deposition using a new arsenic source, tertiarybutylarsine (TBAs). Films with excellent surface morphology were obtained for low V/III values over a wide temperature range (600–800u2009°C), and relatively strong free‐exciton emission was observed in the photoluminescence spectra. Hall measurements indicate carrier concentrations as low as 5×1015u2009cm−3 and mobilities μ300=4000 cm2/Vu2009s. These are equivalent or better than results obtained with trimethylarsenic. In contrast to growth with arsine, the layers were found to be n type for all values of V/III ratio investigated (2–20). Higher quality layers can be expected with source repurification of synthesis via a purer chemical process.

Investigation of carbon incorporation in GaAs using 13 C-enriched trimethylarsenic and 13 CH 4

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.

13C isotopic labeling studies of growth mechanisms in the metalorganic vapor phase epitaxy of GaAs

Isotope tracer techniques using 13C are employed to obtain information on how the alkyl reactants used in MOVPE affect heterogeneous growth process and impurity incorporation reactions. GaAs growth was performed using trimethylgallium, 13C-enriched (50%) trimethylarsine and 13C-enriched (99%) methane. Data were obtained on isotope-labeled effects resulting from substrate crystallographic orientation, gas phase composition and growth temperature. Secondary ion mass spectrometry (SIMS) was used to detect the level of 13C in the deposited films. SIMS sensitivity for carbon species was improved by as much as a factor of 50 by use of the 75As13C− ion at me=88, rather than standard detection at me=13 which is subject to interference from 12CH− ions. Similarly, a factor of 10 increase in 12C sensitivity was achieved by detection at me=87 rather than me=12. The 13C experiments provide the first direct evidence that methyl groups from metalorganic reactants are a major source of carbon in MOVPE grown GaAs films. The measured 13C concentration was as high as 1017cm−3. Carbon incorporation increased with growth temperature, but was independent of the V/III molar ratio. Films deposited on misoriented substrates exhibited a monotomic increase in carbon content as the misoreintation angle from the {001} crystal plane was decreased from 6° to 0°. For substrates with different crystallographic orientations the carbon level was highest for {001} and {011} surfaces, and least for the {111} As face. Addition of 13C-methane to the reactants had no effect on either the growth process or carbon incorporation level. The implications of these results for MOVPE growth models are discussed in detail.

Comparison of alternate As-sources to arsine in the MOCVD growth of GaAs

Abstract We have investigated the use of methyl-, ethyl-, and butyl-based alkylarsine compounds as alternatives to arsine in the epitaxial growth of GaAs. These are all low vapor pressure liquids that can be handled more safely than arsine, which is stored as a high pressure gas. Films were deposited over a wide range of growth conditions ( T g ) = 550-850°C, V/III=2-20) at atmospheric pressure in a horizontal MOCVD reactor. The quality of the films grown with the alkylarsine sources was limited by the presence of both carbon and donor impurities. Isotopic labeling studies using 50% enriched 13 C-trimethylarsine provided direct evidence that the methyl groups from trimethylarsine were a major source of the carbon observed in the films. The effects of source purity and composition on the morphological, electrical and optical properties of the GaAs films will be presented.

Improvements in the heteroepitaxy of GaAs on Si

Successful application of GaAs on Si heteroepitaxy to majority‐carrier device fabrication has recently been demonstrated. However, the quality of the GaAs heteroepitaxial films is considerably below that routinely achieved for films grown on GaAs substrates. We have investigated the initial growth stages of GaAs on Si using ion channeling and double‐crystal ‐ray diffraction, and report improvements in the growth technique leading to higher quality GaAs films. The crystalline perfection of the films was found to be critically dependent on the growth parameters of the initial GaAs buffer layer. Growth interruption after deposition of this layer, followed by an in situ annealing step (10 min at 750u2009°C) prior to final GaAs growth, improved both the structural and optical properties of the films.

Electrical characteristics of InAsSb/GaSb heterojunctions

Heterojunctions of n‐type InAs0.95Sb0.05 grown by metalorganic chemical vapor deposition on n‐type GaSb substrates were studied by capacitance‐voltage and current‐voltage measurements. The n‐n heterojunctions are strongly rectifying and behave like metal‐(n) GaSb Schottky diodes with a barrier height of 0.80±0.02 eV. These measurements establish that the band lineup in this system is of the broken gap variety. We measure the valence‐band offset, Ev(GaSb)−Ev(InAs0.95Sb0.05), to be 0.67±0.04 eV.

Alternative group V precursors for CVD applications

Abstract The chemical vapor deposition (CVD) techniques used to grow III/V semiconductors films, such as metalorganic vapor phase epitaxy (MOVPE), hydride VPE, chemical beam epitaxy (CBE) and gas source molecular beam epitaxy (GS-MBE), all use hydrides (AsH 3 and PH 3 ) as the Group V source. However, the hydrides are extremely toxic gases which are stored under high pressure (200–2000 psi). To reduce the safety hazards associated with these gases, alternative Group V precursors have been investigated. Organoarsenic and phosphorous compounds have received the most attention as replacements for AsH 3 and PH 3 because they are typically low vapor pressure liquids, and thus present significantly lower exposure risks than the hydrides. For AsH 3 these have included the methyl, ethyl and butyl-based derivatives R n AsH 3- n , with varying degrees ( n = 1–3) of hydrogen atom substitution. In this paper the growth properties, thermochemistry and toxicity of the various alkylarsine precursors are compared with arsine. Data are presented on the impact of the thermochemistry of these compounds on film electrical properties, and on the effects of precursor composition and purity on overall film quality. The suitability of alternative As-precursors for device applications is demonstrated, and selection criteria are presented for the most effective alkylarsine compound for a particular CVD growth process.

Investigation of triethylarsenic as a replacement for arsine in the metalorganic chemical vapor deposition of GaAs

GaAs growth experiments have been performed with triethylarsenic (TEAs) to investigate its potential as a replacement for arsine, and to compare the effects on film properties of substituting ethyl for methyl groups in alkyl arsenic sources used in metalorganic chemical vapor deposition. Films were deposited over a wide range of growth conditions (Tg=550–750u2009°C, V/III=2–13), and data were obtained on film electrical and optical properties and variations in growth rate. Growth with TEAs yielded films with good surface morphology, low background doping levels (<1015 cm−3) and 77 K mobilities of 13u2009000 cm2/Vu2009s. Although this represents a considerable improvement over films grown with trimethylarsenic, film properties still appear to be limited by unacceptably high levels of carbon incorporation. Experiments using triethylgallium as the group III source in place of trimethylgallium resulted in substantially reduced and nonuniform growth due to prereaction at the reactor walls.

Epitaxial growth of n+‐n GaAs metal‐semiconductor field‐effect transistor structures using tertiarybutylarsine

We report the first demonstration of metal‐semiconductor field‐effect transistors (MESFETs) made from GaAs structures grown with an alkylarsine source, tertiarybutylarsine (t‐BuAsH2). MESFET fabrication was performed in parallel on t‐BuAsH2 and arsine‐grown wafers to enable direct comparison of device characteristics. The GaAs n+‐n MESFETs made with t‐BuAsH2 exhibited excellent saturation and pinch‐off characteristics, and diode performance comparable to arsine‐grown devices. Although the peak transconductance gm was lower than that achieved with the arsine sample, the form of the gm versus gate voltage curves for the t‐BuAsH2‐grown devices were characteristic of well‐behaved GaAs MESFETs. These initial results demonstrate the capability of t‐BuAsH2 for growing electronic device structures having good carrier transport properties and effective isolation layers.

An integrated laboratory-reactor MOCVD safety system

Abstract A comprehensive MOCVD safety interlock system has been designed and implemented which provides continuous monitoring of critical reactor and laboratory systems. Operator response to system alarms is limited to a single rule — immediate evacuation of the laboratory. The safety interlock system automatically aborts reactor and laboratory operation to predetermined latched states, provides audible and visual indication of the alarm condition, and identifies the detector and location giving rise to the alarm. Computer control of all operating systems enables additional safety to be programmed through interactive software design that eliminates most operator-based errors and provides for safe and reliable reactor operation. A full description is presented of the safety concepts incorporated into the design and construction of the laboratory and reactor system. Since its installation during the past year, the safety interlock system has operated successfully through several power failures and has demonstrated its effectiveness for ensuring a dependable fail-safe environment.