Several fundamental problems are reviewed that must be solved if GaAs on Si growth is to be achieved with device-quality already close to the GaAs/Si interface, rather than relying on thick buffer layers: (a) antiphase disorder, (b) interface charge and cross-doping, and (c) misfit dislocations. An extensive discussion is given of the mechanism by which antiphase disorder is suppressed on (100)-oriented substrates

GaAs and GaAsP with the entire compositional range are grow on Si using an intermediate layer of GaAsP strained superlattices to relax the lattice mismatch. The orientation of the overgrown GaAs layer is found to be determined by the direction of the off-angle of the Si (100) surface. The grown layers are characterized by photoluminescence, x-ray diffraction, electro reflectance and DLTS. GaAs/GaAlAs double heterostructure lasers and GaAsP visible LED's are fabricated on Si substrates. The structural and electronic properties of the grown layers and the device performances are reported in this paper.

Data is presented on the optimization of several molecular beam epitaxial growth processes to provide low dislocation density and high mobility GaAs single crystals on (100) Si wafers. The substrate tilt angle, the growth temperature, and the first buffer layer structure, were investigated Tor this purpose. Using Hall measurements the GaAs layers grown on 2 or 3-degree tilt (100) Si showed consistently high mobilities which are equivalent to the homoepitaxial GaAs mobility. Transmission electron microscopy (TEM) revealed that on tilted (100) Si substrates most of the misfit dislocations were confined within the first 50 Å GaAs layer by forming a type of edge dislocation at the Si surface step edges. Also low temperature grown buffer layers always gave better morphologies and lower etch pit densities while keeping the high mobilities on overgrown GaAs layers.

Successful growth of GaAs on Si has recently been demonstrated. This work is directed toward an understanding of the processes occurring during the growth and their effects on the quality of the GaAs epilayers. Reflection High Energy Electron Diffraction monitoring of the growth in situ shows that the islands that are initially formed coalesce into an epilayer with a 2×4 surface reconstruction. Ion channeling indicates that the crystallinity of the entire epilayer improves with coverage. Substantial reordering of the material occurs when buffer layers grown at low temperatures are annealed at 575°C before and during further growth at this temperature. Comparison of 300 nm layers differing in the growth temperature of the first 100 nm shows no variation in the crystallinity as determined by ion channeling. Surface morphology degrades, however, and 77K photoluminescence intensity rises with the initial growth temperature. The optical and structural properties of 2μm thick films are also discussed.

Direct observations of early stages of growth of GaAs on (100)Si are presented. Cross sectional TEM and plan view SEM images show three dimensional island growth, for growth above 300°C. Island size, island spacing, surface morphology and stacking fault defect spacing all decrease with substrate temperaturefor fixed Ga and As2 fluxes. Below 300C, 7nm thick films are uniform. Diffusion-controlled growth kinetics are inferred.

In recent years, the heteroepitaxial growth of GaAs layers on Si substrates has been gained an increasing interest [1 - 14]. GaAs is one of the most important III-V materials and has been well studied and used for optical and electrical devices. On the other hand, with Si we have large size wafers of superior quality and sophisticated technologies and Si is a main material for semiconductor industries. Therefore, GaAs/Si system has possibilities for realizing new types of functional devices or ICs with GaAs and Si devices. This system, however, has two serious problems. One is the large lattice mismatch of about 4 % between these materials and the other is the polar on nonpolar problem i.e., the formation of an antiphase domain disorder. It was reported that when (211)-oriented Si substrates were used, there was no problem of the formation of an antiphase domain structure 5. For growing materials on lattice mismatched substrates, it was reported that the thin layers deposited at low temperatures were effective to relax the lattice mismatches for the systems such as SiC on Si[15] and Si on saphire [16]. In GaAs/Si system, the Ge buffer layer has been used to relax the lattice mismatch[17 - 22] It was also reported that the composite strained layer superlattice with GaP/GaAsP and GaAsP/GaAs was very effective as a buffer layer[23 - 25].

An approach to the composite layer growth of GaAs/Ge on Si(100) and insulator–coated Si(100) has been investigated. To overcome a problem of antiphase disorder of GaAs occurring along with epitaxial growth on Ge, thermal etching on Ge surfaces in hydrogen was introduced just prior to the growth. Antiphase–domain–free GaAs grown on a Ge(100) wafer exhibited mirror surfaces, photoluminescence characteristics comparable to those of homoepitaxial layers, and low etch–pit densities. The autodoping of Ge into GaAs induced a highly doped interfacial layer several thousand angstroms thick. The present study also involves heteroepitaxial growth of Ge on Si by vacuum deposition and Ge crystal growth on insulating layers over Si by LESS method.

The ability to grow high quality epitaxial GaAs films directly on Si substrates has recently been demonstrated by Molecular Beam Epitaxy. Many of the most successful growth techniques include initial growth at low temperatures and slow growth rate to nucleate the compound on the elemental semiconductor with subsequent normal growth under conditions used for homoepitaxial GaAs MBE. The mechanisms for the success of this method are still poorly understood. This work focusses on a study of the structural evolution of this low temperature initial layer and conventionally grown overlayer. Thin films in the 5 to 300 nm range were used to evaluate the effect of the temperature and thickness on the growth process. Thicker films, described elsewhere, were used to evaluate the crystalline and optical quality of potential device layers.

The structure of the thin buffer layers was studied as a function of both temperature and thickness. The crystalline quality of these layers was found to be quite poor, with substantial disorder at the GaAs/Si interface. The quality improved slowly as a function of thickness. The effect of the conventional overgrowth on this initil layer was also investigated. It was found that the quality of the low tumperature layer improved as normal overgrowth continued, as measured by ion channeling aligned yields. After 200 nm of overgrowth, ion channeling aligned yields from the material at the interface had declined substantially. This indicates that substantial regrowth and annealing of defects occurs as growth continues. These observations are further confirmed by TEM.

Recent studies have shown that high quality GaAs films can be grown by MBE on Si substrates whose surfaces are slightly tilted from the (100) plane. In order to investigate the effect of the tilting of substrate surfaces on the formation of threading dislocations, the GaAs/Si epitaxial interfaces have been observed with a 1 MB ultra-high vacuum, high voltage electron microscope. Two types of misfit dislocations, one with Burgers vectors parallel to the interface and the other with Burgers vectors inclined from the interface, were found in these epitaxial interfaces. The observation of crosssectional samples perpendicular to each other has shown that the tilting of the substrate surface directly influences the generation of these two types of misfit dislocations. The mechanism of the reduction of threading dislocations by the tilting of the substrate surface is discussed based on these observations.

We report some results on the chemical, structural and electrical characterization of Ge and GaAs films, grown on Si (100) substrates by electron-beam evaporation and MOCVD, respectively. Good quality Ge films have been obtained at 700°C substrate temperature at a growth rate of 5 nm/sec in 5 × 10−7 torr. Similarly, good GaAs films were obtained at 650°C and at 0.3 nm/sec. RBS data for GaAs films (1.1 μm) show Xmin approaching 3.5%, and Ge films (1.5 μm) around 3.6%. Photoluminescence of the same films show peaks around 852 nm with FWHM of 14 meV. Cross-sectional TEM and etching show a near-exponential decrease in defect density away from the Ge/Si interface. Detailed characterization results of the S-R, I-V, C-V, and X-ray studies are also described.

Recent progress in the research of heteroepitaxial growth of Si, Ge, and GaAs films on CaF2/Si structures is reviewed. Growth conditions and material properties of the Si/CaF2/Si structures are first discussed. It is shown that such growth techniques as the predeposition technique and the recrystallization method are useful to improve the crystalline quality of Si films on the CaF2/Si structures. Then, device application of the Si/CaF2/Si structure to field effect transistors with epitaxial MIS (metal-insulatorsemiconductor) gate electrodes is described. Finally, epitaxial growth of Ge and GaAs films on the CaF2/Si structure are discussed, in which such growth parameters as the substrate temperature and growth rate are optimized to obtain high-quality films with excellent crystallinity and smooth surface.

We have extended our studies of epitaxial insulator-metal-semiconductor heterostructures composed of CaF2 and CoSi2 layers grown on Si(111) substrates to cover a broader range of growth conditions. We find that rapid thermal annealing plays a crucial role in optimizing the epitaxial quality of the CaF2 layer over the entire range of conditions studied. The chemical stability of the fluoride layer is also enhanced by the annealing process.

We report for the first time the growth of GaSb/AlSb multilayers and alloys on Si(100) by molecular beam epitaxy. High quality films were achieved in spite of the large lattice constant mismatch of 12%. Room temperature, optically pumped pulsed lasers emitting at 1.8μm have been demonstrated. Lateral photoconductive detectors with responsivities of 0.18 A/W have also been made. The film nucleation on the Si substrate was observed in-situ by reflection high energy electron diffraction. Characterization of the grown epilayers and preliminary optical device results are described.

In this paper, a study is made of the electrical properties and of the types of structual defects which can occur in epitaxial CaF2 grown on Si(111) substrates by molecular beam epitaxy (MBE). High-resolution transmission electron microscopy (HRTEM) and high-energy (≥2 MeV) He+ ion channeling techniques are used to characterize defects in the epitaxial layer and at the CaF2 /Si interface while current-voltage (I–V) and capacitance-voltage (C–V)3 measurements are used to characterize the electrical properties. The HRTEM images show an atomically abrupt interface between the CaF2 and Si. The most common defect we have been able to identify is associated with an atomic step at the interface and is similar to a Shockley partial dislocation at a (111) twin interface in an fcc crystal structure. The ion channeling measurements also indicate the presence of defects at the CaF2 /Si interface. The apparent defect density measured by ion channeling decreases in the CaF layer as one moves away from the interface at a rate which depends on ihe final thickness of the epitaxial film. Ion channeling has also been used to measure strain and it is found that, while thin layers of epitaxial CaF2 on Si(111) have large strain, the strain becomes vanishingly small as the layers exceed 200 nm in thickness. This result can be adequately explained using an equilibrium model for the introduction of strain relieving misfit dislocations and indicates that epitaxial fluoride layers may be useful as thermal mismatch buffers in heteroepitaxial structures. In C–V measurements of epitaxial CaF2 layers on Si(111) which have been fabricated into metal-insulator-semiconductor structures, the capacitance is observed to remain constant over a large variation in applied voltage. This constant capacitance region can be explained as due to a high density of interface states in the band gap. In addition, I–V measurements indicate that, at low fields, the CaF2 resistivity exceeds 1014 Ω-cm. At high fields, the CaF2 starts to conduct in a manner which we speculate is due to defects at the CaF2/Si interface. The field at which this conduction takes place has been ovserved to exceed 1 MV/cm for a 42-nm-thick CaF2 film with the device geometry used for this work.

Single crystalline epitaxial GaAs layers have been grown on silicon substrates with a thin germanium interlayer. All semiconductor layers were deposited by the chemical vapor deposition technique. The surface condition of the silicon substrate is an important factor affecting the quality of GaAs/Ge films on silicon. P+/n homojunction solar cells of 0.25 cm2 area with an AM1 efficiency near 12% have been prepared.

Four layer HgCdTe/CdTe/GaAs/Si structures have been prepared by the sequential growth of (100) GaAs on (100) Si by MBE, (100) CdTe on GaAs/Si by congruent evaporation in UHV and (100) HgCdTe on CdTe/GaAs/Si by vapor transport. Infrared transmission, X-ray rocking curves, differential interference contrast microscopy and selected area electron channelling patterns characterize the structures.

Remarkably good device performance at both dc and microwave frequencies has recently been obtained from GaAs based devices grown on Si substrates. In GaAs MESFETs on Si, current gain cutoff frequencies and maximum oscillation frequencies of fT = 13.3 GHz and fmax = 30 GHz have been obtained for 1.2μm devices, which is nearly identical to the performance achieved in GaAs on GaAs technology for both direct implant and epitaxial technology. For heterojunction bipolar transistors, current gain cutoff frequencies and maximum oscillation frequencies of fT = 30 GHz and fmax = 11.3 GHz have been obtained for emitter dimensions of 4×20μm2. In GaAs AlGaAs MODFETs. current gain cut-off frequencies of about 15 GHz with lμm gates were obtained on GaAs and Si substrates. The pseudomorphic InGaAs/GaAs MODFETs were also fabricated and found to be comparable to GaAs MODFETs although they should perform better. The structures were also shown to maintain their properties when put through ion implantation and annealing process. Given the performance already demonstrated in GaAs on Si devices and the advantages afforded by this technology, the growth of III-Vs on Si promises to play an important role in the future of heterojunction electronics.

One approach to the development of optical interconnects between Si systems utilizes diode lasers fabricated in III-V epitaxial layers grown on Si wafers. We have fabricated double-heterostructure lasers in GaAs/AlGaAs layers grown on a Ge-coated Si substrate, and both asymmetric largeoptical- cavity (LOC) lasers and graded-index, separate-confinement heterostructure (GRIN-SCH) lasers in such layers grown directly on a Si substrate. The GaAs/AlGaAs layers were grown by molecular beam epitaxy on (100) p-Si substrates. Si and Be were used as the n- and p-type dopants, respectively. Oxide-defined stripe-geometry devices, 300 μm long, were fabricated using standard AuSn and CrAu metallizations for the n- and ptype contacts, respectively. The laser facets were formed by ion-beamassisted etching. The double-heterostructure devices (8 μm stripe width), in which the active region contained about 10 mole percent AlAs, were evaluated using pulsed bias at 77 K. They produced power outputs up to 3.3 mW per facet and exhibited thresholds as low as 170 mA. The LOC devices (4 μm stripe width), which had a GaAs active region, were characterized using pulsed bias at 300 K. These devices produced power outputs up to 27 mW per facet. The lowest threshold was 775 mA. The GRIN-SCH devices (4 μm stripe width), which incorporated a 70 Å GaAs quantum well active layer, were also characterized using pulsed bias at 300 K. These devices were not operated at power outputs above −5 mW. Their lowest threshold was 220 mA.

Integration of Si MOSFETs with GaAs MESFETs and with GaAs/AlGaAs double-heterostructure LEDs on monolithic GaAs/Si substrates is reported. Both Si MOSFETs and GaAs MESFETs show characteristics comparable to those for devices fabricated on separate Si and GaAs substrates. In LED/MOSFET integration, the cathode of each LED is connected with the drain of a MOSFET. This is the first time that Si and GaAs devices have been monolithically interconnected. LED modulation rates up to 27 Mbps have been achieved by applying a stream of voltage pulses to the MOSFET gate.

The characteristics of GaAs MESFETs in GaAs-on-Si have been studied in detail for digital IC applications. The device structure utilizes GaAs and AlGaAs undoped buffer layers grown on a 3 degrees off (100) silicon substrate by MBE. The threshold voltage of the MESFET is adjusted by recessing the gate.

The maximum observed transconductance of 135 mS/mm is comparable to what is expected from the bulk GaAs device with the same parameters. The device also shows good pinch-off characteristics. Both enhancement and depletion mode MESFETs have been fabricated.