Device quality GaAs was grown in a conventional Organometallic Chemical Vapor Deposition (OMCVD) reactor, using sequential group III and V reactant gas exposures typical of Atomic Layer Epitaxy (ALE). The importance of gas phase concentration transients during the ALE cycles was revealed by systematic investigations of the effect of the sequences used, for the cycles, on impurity incorporation as well as on the growth rates. In this study, we attempt to quantify the effects of such transients by solving the diffusion equation for the reactant gases, with initial conditions specific to ALE. We used this model to calculate the time dependence of the reactant gas concentration at the growing surface. This quantitative study gives us new insights into the ALE technique and confirms that the V/II ratio at the substrate surface can be controlled by the choice of the gas sequence.

The saturation behavior of growth of GaAs and InAs by atomic layer epitaxy is studied. The growth rate is found to be strongly dependent on alkyl exposure time for the same total alkyl exposure per cycle. The longer the exposure time, the higher the saturated growth rate is. For short exposure, the growth rate saturates to a value less than one monolayer (ML)/cycle. Strong saturation of the growth rate to one ML/cycle is achieved for InAs at a growth temperature of 340°C with 3 sec of trimethylindium exposure. For GaAs, saturation of the growth rate to one ML/cycle is achieved at the growth temperature of 400°C with 10 sec of trimethylgallium exposure. At higher growth temperatures, the growth rate does not saturate but increases slowly with increasing exposure. The large physical size and finite decomposition time of the initial adsorbate are suggested as the cause for the dependence of ALE growth rate on alkyl exposure time.

A major limitation to the continuing development of organometallic vapor phase epitaxy (OMVPE) for the growth of II/V semiconductor materials is the hazard posed by the hydride sources, AsH3 and PH3, which are virtually universally used, in high pressure cylinders, as the group V source materials for the growth of the highest quality materials. The set of stringent requirements for an organometallic group V source, which includes a high vapor pressure (>50 Torr) and freedom from undesirable carbon contamination, eliminates most commonly available non-hydride group V sources. Recent research on newly developed sources has shown considerable promise. The entire area of group V sources, including the elemental sources, for OMVPE growth of II/V materials will be reviewed. The sources with no hydrogen atoms attached to the group V atom, the elemental, trimethyl-V, and triethyl-V, sources all appear to give unacceptably high carbon incorporation, as does dimethylarsine. Diethylarsine, which has one H attached to the As, produces high quality GaAs. Tertiarybutylarsine (TBAs) and tertiarybutylphosphine (TBP) appear to be promising source materials. TBP has a very low toxicity, a vapor pressure ideal for OMVPE growth, and the pyrolysis occurs at lower temperatures than for PH3. No carbon contamination can be attributed to the TBP. Control of the As/P ratio in OMVPE grown GaAsP is much improved for TBP as compared with PH3 due to the more rapid pyrolysis. TBAs has similar attributes including a favorable vapor pressure and lower pyrolysis temperature than AsH3. The substitution of TBAs for AsH3 results in no observable increase in carbon in the epitaxial GaAs. Phenylarsine is a similar source, with a phenyl radical substituted for a single H atom on AsH3. The vapor pressure of phenylarsine is quite low and the pyrolysis temperature is expected to be some what lower than that for AsH3. Limited results indicate that carbon incorporation in GaAs is acceptable only when TEGa is the group V source.

The chemical kinetics of two new organometallic arsenic substitutes, tris-trifluoromethylarsenic (As(CF3)3) and phenylarsine (PhAsH2), for use in the MOCVD of GaAs have been characterized through the use of microbalance gravimetry and molecular beam mass spectrometry. Both growth rate and gas-phase cracking studies demonstrate that phenylarsine interacts only slightly with the common gallium precursors, which may make it a useful alternative to arsine. Growth with tris-trifluoromethylarsenic is achieved only at low V/III ratios and with pressures above 250 Torr. The compound etches GaAs under most conditions.

Vapor pressures of commercial electronic grade TMA,.TMG and TMAs samples have been measured at various temperatures and compared with those of known pure samples. Only TMA showed the presence of impurities. The UV absorption spectrum of impure TMA shows toluene to be an impurity. The UV absorption cross sections of TMA, TMG and TMAs have been measured and tabulated at several wavelengths.

Very high carbon impurity levels (1018-1021cm−3) in GaAs films grown using triethylarsenic (Et3As) and trimethylgallium (Me3Ga) can be dramatically reduced by substituting a portion of the Et3As reagent with arsine during growth. Gallium arsenide epilayers grown at a deposition temperature of 560°C, a total V/III ratio =10, and the Group V reagent consisting of a mixture of Et3As and arsine, were found to exhibit carbon levels of only 5-7×1015cm−3for Group V mixtures ranging from 0-65% Et3As. All of these films were n-type, except for those grown using 100% arsine, which were p-type. The reduction in carbon incorporation in films grown using Et3As and arsine as co-reagents is shown to result from a unique, synergistic, reaction chemistry involving the two arsenic reagents. In particular, the decomposition of arsine to provide carbon-free, active arsenic fragments for growth is greatly enhanced by the presence of Et3As as a co-reactant.

The rapid growth of the microelectronics industry has spawned environmental problems associated with the process gases used to prepare semiconductors. Historically, many of these problems have been ignored because relatively low volumes of gases are associated with semiconductor fabrication; however, the exceptionally high toxicity of these materials (e.g. arsine, phosphine, silane, etc.) can cause major problems, especially for small quantity hazardous waste generators. Large commercial users have built expensive facilities for handling these materials, but small quantity generators typically have vented to the atmosphere through their exhaust ductwork. This is particularly true during cylinder changes where the gas manifold is repeatedly purged into the ductwork of the facility with no other treatment.

A new family of novel vent gas scrubbers that will cost-effectively reduce toxic air emissions below the Threshold Limit Value (TLV) during cylinder changes is described. Called a vent gas scrubber (VGS), this device combines high capacity, high selectivity and very high capture-effectiveness. These properties permit the VGS to be extremely compact (ca. 125 ml), last a long time in use (several years or more) and to reduce emissions to well below the TLV for improved gas handling safety.

This paper presents proposals for the synthesis of several group III metal organics (In, Ga, Al compounds) and preliminary results on their use in the MOVPE (metal organic vapor phase epitaxy) of III-V semiconductors. The common feature of all these precursors is that they are saturated by interor intramolecular coordination. They are even non-pyrophoric and air resistant which is an interesting aspect with respect to safe handling. In addition, the compounds are liquid at room temperature with a low but sufficient vapor pressure for MOVPE without additional heating of the source.

Using an alternate arsenic source, namely, Tertiary Butyl Arsine, a concentrator GaAs solar cell has been grown in a low pressure metal organic chemical vapor deposition reactor. Under 72 sun, air mass 1.5 illumination, the cell had an open circuit voltage of 1.1 V, a fill factor of 83% and an overall efficiency of 21%.

This paper discusses recent improvements achieved in the growth of epitaxial layers of GaAs and AlGaAs using the liquid arsine substitute tertiarybutylarsine (TBA) and metal alkyls. The high purity TBA now available yields undoped GaAs with residual donor/acceptor concentrations in the low 1014 cm−3 range. Under optimized growth conditiorp the layers are either n-type and have 77*K mobilities up to 85,000 cm2 //Vs or they are compensated or p-type. For aluminum gallium arsenide, layers grown with TBA have properties similar to arsine-grown material as demonstrated by low temperature photoluminescence (PL). The PL efficiencies and line widths of the TBA-grown AlGaAs samples are comparable to those prepared with arsine.

The replacement of arsine and phosphine in a hot-walled VPE reactor by Group V alkyls is described. Epitaxial layers of lnP and InGaAs were grown using trimethylarsenic and trimethylphosphorus respectively. The surface morphology obtained was equivalent to that of samples grown using arsine and phosphine. InGaAs samples with no intentional doping were n- type with a background carrier concentration of 6 × 1015 cm−3, about 3 times higher than that of comparison samples grown using arsine. Mobilities measured at 77 K and 300 K respectively were similar to those measured for corresponding samples grown using arsine, suggesting that no significant carbon incorporation occurred. InP was n-type with a background carrier concentration of 3-6 × 1017 cm−3, significantly higher than that of samples grown using phosphine. Preliminary SIMS measurements on the layers suggest that this is due to silicon-based impurities in the trimethylphosphorus. Results reported for MOCVD using arsenic and phosphorus alkyls are contrasted with present results for a hot-walled reactor.

The the Halide-CVD technique is used in both research and development as well as production at AT&T. The unique requirements of the production environment dictate that reactor designs include features to improve reproducibility and maintenance, as well as reduce operator intervention. Features incorporated in the Halide-CVD reactor at AT&T include microprocessor control of valves, mass flow controllers, and furnace temperature setpoints. The unique needs of a production facility, such as process reproducibility, and commonality with standard plant equipment and information systems, will be highlighted.

A new, large-scale, barrel-type MOCVD reactor which is capable of pro- ducing seven 3-inch wafers or fourteen 2-inch wafers at a time has been developed. Experiments and computer modelling studies of this geometry have been performed. The physical and electronic properties of n-type GaAs as a function of growth conditions are presented. Through the use of experimental design methods, the growth process has been optimized to yield highly uniform growth rates. The demonstrated uniformity supports the use of this reactor for production environments requiring 3-inch wafers.

The epitaxial growth of GaAs/AIGaAs layers and multilayer structures has been investigated in different low pressure horizontal multiwafer reactors for high throughput capable to handle several 2“ and 3“ wafers in one run. The growth behavior in these reactors will be described with respect to gas flow dynamics. The background carrier concentration is in the 1014 cm−3range. The uptake of dopants (SiH4) is strongly reduced upon pressure reduction.

The uniformity of GaAs and AIGaAs layer thickness is better than ±3 % over 3“ diameter substrates. The uniformity of composition (measurer on HEMT structures) is better than ± 1 % across 98 % of the wafer areas (± 0.5 % across 75 %). Also the reproducibility is better than 1 %. Results on the uniformity of dopant distribution will also be presented.

HEMT structures grown at low pressure conditions show mobilities of 100,000 cm2/Vs at 77 K and over 210,000 cm2/Vs at 20 K (ns= 6×1011 cm−2, spacer thickness 9 nm). HEMT devices with transconductance of 330 mS/mm could be achieved.

Metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) are well established methods for growing epitaxial GaAs and AlGaAs films. However, MOCVD equip- ment uses the highly toxic gas, arsine, and MBE equipment is very costly and coats only one wafer at a time. We have developed a vacuum chemical epitaxy (VCE) reactor which avoids the use of arsine and allows multiple wafers to be coated in a production environment.

We review the growth of GaAs on Si by MO-CVD and MBE and discuss the relative merits of these techniques. Major emphasis is placed on the structural and optical characterization of the material that may be indicative of device performance. Typical GaAs layers on Si are free of anti- phase domains and the crystallinity at the surface for a 3-4μm thick deposit approaches that of bulk GaAs, as evidenced by the RBS backscattering yields and Si ion implantation profiles. The major drawbacks of GaAs heteroepitaxy on Si are the very large dislocation densities (106 - 109cm−2), the relatively high unintentional doping concentration (>5 × 1014cm−3 ) that is partly attributable to Si outdiffusion, and the excessive bowing due to thermal expansion coefficient mismatch. While there are growth and processing techniques to overcome bowing or at least its influence, dislocations and low resistivity are hard to remedy. We discuss novel schemes to reduce dislocations (selective area growth, superlattices and thermal cycling) and efforts to improve the electrical properties (doping, optimization of V/III ratio). A variety of electronic devices and circuits have been fabricated using GaAs/Si. We shall present results on MESFETs, HBTs and HFETs processed in our laboratory and elsewhere. It is quite encouraging that HFETs with a transconductance of 220mS/mm are achievable. However, lasers in room temperature CW operation still have a very limited lifetime. Finally, we discuss the implications of GaAs/Si for a broader area of mismatched heteroepitaxy (InP/Si, InP/GaAs, etc.) and speculate on the future prospects for this new materials technology.

Heteroepitaxial growth of GaAs, InP, GaP and InGaP on Si substrates is studied using MOCVD (Metal-Organic Chemical Vapor Deposition). High qgaliti GaAs films on Si, with a dislocation density of about 106 cm−2, are obtained by combining strained- layer superlattice insertion and thermal cycle annealing. Reduction of dislocation density in the III-V compounds on Si is discussed based on a simple model, where dislocation annihilation is assumed to be caused by dislocation movement under thermal and misfit stress. As a result of dislocation density reduction, high-efficiency GaAs-on-Si solar cells with total-area efficiencies of 18.3% (AMO) and 20% (AM1.5), and red and yellow emissions from InGaP-on-Si light-emitting diodes (LEDs) have been realized.

We report growth by MBE and fabrication of state-of-the-art AlGaAs/GaAs selectively doped heterostructure transistors (SDHT's) and ring oscillators on Si substrates. In MBE growth, use of minimum As4/Ga flux ratio during initial nucleation combined with in-situ thermal cycles gave a marked improvement in material quality. Although undoped GaAs buffer layers were highly resistive and were fully depleted under a Schottky contact, a parallel n-type conduction path confined in a thin region (<0.1 pm) near the GaAs/Si interface was sometimes observed whose sheet density (1012 - 1013 cm−2) and mobility (600-900 cm2V−1 s−1) were independent of temperature between 77K and 300K. This parallel conduction did not affect the dc behavior and switching speed of SDHT's, and it was successfully prevented by doping the GaAs with Be near the interface. For a 2DEG sheet density of 1012 cm−2, a mobility as high as 53,500 cm2V−1s−1 at 77K was obtained, as against a mobility of ∼70,000 cm2 V−1 s−1 for a similar structure on GaAs substrates. For 1 μm-gate-length devices, maximum transconductances of 220 and 365 mS/mm were measured at 300K and 77K, respectively. A minimum propagation delay time, Td, of 28 ps/stage was measured at 300K for direct coupled FET logic (DCFL) ring oscillators for 1.1 mW/stage power dissipation. rd reduced to 17.6 ps/stage at 77K. From microwave S-parameter measurements at 300K, current gain and power gain cutoff frequencies of 15 GHz and 18 GHz, respectively, were measured. These results are comparable to the SDHT technology on GaAs substrates.

A systematic study pertaining to the molecular beam epitaxial growth and charac- terization of GaAs films on various crystallographic orientations of sapphire is presented. For integration with silicon circuitry, heteroepitaxial GaAs layers have also been grown on commercially-available chemical vapor deposited silicon-on-sapphire (SOS) and SOS substrates that have been upgraded by the double solid-phase epitaxy process.

High quality of Si-doped n-type MBE GaAs grown directly on 4° off (001) towards [0111 Si substrates has been achieved by a multiple step MBE growth procedure. Epilayers have been characterized for the doping range 2x1016 to 3x1018cm-3 with thickness up to lOm by double crystal x-ray rocking curves, Hall mobilities, photoluminescence spectra, dislocation etching pit densities and I-V characteristics of MESFET of GaAs/Si. The results show that the electron mobilities are 2900 to 1430cm2 /Vs while free electron concentration of 3.5x1017 to 2.7x1018cm-3. The FWHM of the DCRC are 175 to 350 arc sec, the EPD are 1x106 to 2x107 cm-2 for most of samples and both of them appear variation with thickness of epilayer. The main peak of PL appears a few meV shift to long wavelength in comparison with GaAs on GaAs. The FWHM of the PL are 21 meV for n-type GaAs/Si in a doping level of 3.5x1017cm-3. MESFET show a acceptable I-V characteristics. All of epilayers with thickness less than 5pm appear good morphology. Some slightly orthogonal cracking was observed in the 5 to 10µm thick films of GaAs/Si.