GaAs has been successfully grown by LPE on partly covered (windowed) GaAs-on-Si substrates prepared by MBE. Almost dislocation-free layers were obtained in narrow stripe windows. The grown layers were characterized by photoluminescence and Hall effect measurement. The photoluminescence polarization indicated that a uniaxial tensile stress along the stripe direction is applied in the mesa stripe LPE layer while it is biaxial in the wide GaAs layer on Si. The stress relaxation in the direction perpendicular to the stripe is discussed.

Epitaxial gallium arsenide films have been deposited on single crystalline GaAs substrates of {100} orientation and Si substrates of 3° off the {100} orientation by ArF excimer laser-induced metalorganic chemical vapor deposition. The important process parameters include the cleanliness of the substrate surface, substrate temperature, the composition, flow rate, and pressure of the reaction mixture, and the pulse energy and pulse rate of the laser. Particular attention was directed to the in-situ cleaning of the substrate surface prior to the deposition process. Homoepitaxial gallium arsenide films of good structural perfection have been deposited at 425°- 500 ° C and their single crystallinity has been confirmed by transmission electron microscopy. The carrier concentration decreases with increasing AsH3/(CH3)3 Ga molar ratio and with decreasing substrate temperature. Lower growth rate during the initial stage of deposition is necessary to obtain heteroepitaxial gallium arsenide films on Si with good structural perfection. The TEM examination of GaAs films of 0.15–0.2 µm thickness deposited on Si substrates at 500 °C has shown that stacking faults were present in the GaAs films; however, there is no apparent threading dislocations in the surface region of the thin GaAs film.

Epitaxial SiGe buffers have been formed by the implantation of 74Ge+ ions into Si(100)4° to <011> substrates. The implants were made at 150keV to a dose of 1×1017 /cm2 . The epitaxial layers were characterized by Rutherford backscattering, Raman spectroscopy, and electroreflectance and were found to be 300Å thick having on average a composition of Si0 . 35 Ge0.65. GaAs layers were then grown on these substrates by molecular beam epitaxy, using the standard two-step growth process. The results from Auger, Scanning Electron Microscopy, and Cross-sectional TEM indicate a lower defect production and propagation in these samples, compared to those grown directly on Si.

The monolithic integration of GaAs and Si devices is highly attractive for very high speed LSI and optoelectronic integrated circuits. To accomplish this, the epitaxial growth of GaAs films on Si substrates has been successfully realized. However, in the GaAs/Si structure, the conductive nature of the silicon substrate results in a severe transmission line loss [1,2]. To help solve this problem, we suggest to grow GaAs film on SOI (silicon on insulator) substrate for microwave device application. This GaAs/SOI structure will have low transmission line loss and excellent radiation hardness. In this paper, we present some cross-section SEM and TEM data and discuss the transmission line loss and radiation hardness of this multilayered structure.

The recent demonstrations of room-temperature cw operation of diode lasers fabricated in GaAs/AlGaAs layers grown on Si wafers have encouraged efforts to develop monolithic GaAs/Si integration technology for applications such as optical interconnects between VLSI subsystems. This paper summarizes our current work in this area, which is focused on the development of a highspeed, MSI-scale monolithic GaAs/Si test chip that integrates Si MOSFET circuits with diode lasers, LEDs, photoconductive detectors, and MESFET logic circuits fabricated in GaAs/AlGaAs layers grown by molecular beam epitaxy. Growth issues and processing considerations that affect device and circuit performance are addressed, and the characteristics of LEDs monolithically integrated with Si driver circuits and of GaAs microwave MESFETs fabricated on high-resistivity Si substrates are reported.

We present DC characteristics of all-OMCVD grown GaAs MESFET structures on Si substrates with unintentionally doped GaAs or AlGaAs buffer layers. MESFETs fabricated in two and three inch GaAs on Si wafers pinch off well and exhibit reasonably high transconductances up to 110 mS/mm for 1 µm gate devices. The reverse Schottky breakdown voltage of the MESFET gate is as high as 15 V and the forward turn on voltage is ~0.65 V. The ohmic isolation is comparable to the typical homoepitaxial layer with a leakage current of 100 nA at a I V bias. The low background doping levels of unintentionally doped GaAs buffer layers is the key factor for this successful MESFET operation.

GaAs layers free of antiphase domains (APD's) have been grown by molecular beam epitaxy (MBE) on nominally (001)-oriented Si substrates. This is achieved by preheating the substrates at 950 °C over 60 min or at 1000 °C over 5 min in an ultrahigh vacuum. The maximum Hall mobility at 293 K is 5300 cm2 /Vs for the APD-free GaAs layer doped with Si at a concentration of 2×1016 cm−3 . Selective epitaxial growth of GaAs has been carried out on a Si substrate pattrened with SiO2, which was formed by wet O2 oxidation. By choosing an appropriate thickness of the SiO2 layer, the warpage of wafers can be reduced to zero. While single-crystalline GaAs is grown on Si-exposed areas, highly-resistive (ρ ≧ 105 Ωcm) poly-crystalline GaAs is deposited on SiO2 . This technique has been successfully applied for the device isolation of modulation-doped FET's (MODFET's, HEMT's, etc.) on Si without mesa-etching. The transconductance of the MODFET with a 3 µm-long gate reaches 88 mS/mm at 293 K.

We have found that the surface morphology of GaAs grown on Si by MBE is smoother at lower growth temperatures (<500° C), but that the crystalline properties improve at higher growth temperatures (575-600°C). After thermal annealing at 850°C for 15 rai the TEM plan-views indicate that the dislocation density on the surface is reduced by a factor of 4 only. However, the TEM cross-sections indicate a much larger reduction of dislocations in highly dislocated regions near the GaAs/Si interface. Dislocations which are loops or tangles tend to shrink and clean up after annealing leaving a larger volume of GaAs free from, or with fewer, dislocations. The density of electron deep levels reduces with increasing thickness. Electron traps M1, M3 and M4 are not seen when a high purity As is used. For high device performance, the GaAs buffer layer thickness should be at least 2 µm. Although the wafer warpage increases from 7 µm to 52 µm as the GaAs thickness increases from 1.2 µm to 4.2 µm on 7.5 cm wafers, the wafers are as fiat as the original Si wafers under vacuum clamping. Wafer warpage reduced significantly when GaAs was grown selectively through a Si shadow mask. For 1 µm gate MESFET's, σvT was 65 mV on a 3.5 × 3 cm2 wafer area with gmax = 153 mS/ram. A minimum propagation delay of 52 ps/stage at a power dissipation of 1.3 mW/gate was measured for the 19 stage DCFL ring oscillators with 40= yield. Conductivity of the Si substrate and GaAs buffer layer posed no problem in channel isolation. The divide-by-two circuits performed the frequency dividing operation up to 1.8 GHz. The study shows that GaAs-on-Si has a great potential for digital IC's.

Capacitance transient spectroscopy has been applied to identify deep levels associated with heteroepitaxial GaAs grown on silicon. Results from p+n diode test structures reveal creation of the electron trap EL2 and a high density of hole states in the bandgap. This is the first reported observation of hole traps in MBE GaAs on Si. The activation behavior of the electron and hole signal peaks fits the signature of two different charge states associated with EL2, a native point defect complex seen in MOCVD, VPE, and bulk-grown GaAs, but not usually observed in MBE grown GaAs. Interstingly, the spectra seen show many similarities with earlier deep level transient spectroscopy (DLTS) observations on plastically deformed GaAs.

Patterned epitaxial GaAs films have been formed on Si substrates by either growth over patterned substrate (selective -area epitaxy) or chemical etching of patterns after growth. The optical properties of these samples are studied by 77K photoluminescence (PL) and the defect structures are investigated by transmission electron microscope (TEM). The patterned substrate consisted of bare Si stripes with width ranging from 10 µm to 100 µm surrounded by Si3N4 films on both sides and a reference area of bare Si. For 1.5 µmiann d 3 µm thick films, PL intensities from the films inside the 10 µm stripe shows 140% and 75% increase over unpatterned areas while the residual tensile stress in the patterned films is very similar to that of the unpatterned area. The increase in the photoluminescence intensity is ascribed to the reduction of crystalline defects inside the the window area. In the chemically etched sample, the pattern consisted of 4 µm by 4 µm squares and 1 mm long stripes with widths ranging from 100 µm to 4 plm. From the shift of PL peaks, a monotonic decrease in the tensile stress versus stripe width is observed. In particular, when the width of the stripe is less than 7 µm. tensile stress becomes essentially uniaxial in agreement with the results obtained by Yacobi et al [16] on a GaAs on InP sample. The polarization of the luminescence spectra parallel and perpendicular to the uniaxial stress of a 4 µm wide stripe agrees well with theoretical prediction. It is also observed that tensile stress is almost completely relieved in the 4 µm by 4 muentc hed squares.

Spatial homogeneity of the luminescence and electrical properties of gallium arsenide films grown directly on silicon substrates (GaAs/Si) by molecular beam epitaxy (MBE) have been investigated with microscopic scanning photoluminescence (PL), cathodoluminescence (CL), electron beam induced current (EBIC), and scanning deep level transient spectroscopy (SDLTS). It was found that GaAs/Si exhibits a highly nonuniform lateral distribution of speckled appearance in CL and PL images. These centers are also responsible for short minority carrier lifetimes as determined by EBIC. The observed nonuniformities appear to be a fundamental material property which is not altered by post-growth annealing. Correlations between the luminescence and electrical inhomogeneities and structural defects will be discussed.

Low temperature (T - 5K) photoluminescence (PL) has been measured on a variety of as-grown and annealed GaAs films grown on Si substrates by the MBE technique. The PL spectra of the annealed GaAs layers showed an apparent difference between the nomigally undoped samples with free carrier concentrations below 1015 cm−3 and the layers with dopant concentrations exceeding 1017 atoms cm−3 . The annealing caused an increase of both excitonic and defect related PL intensities in low doped samples. In heavily doped layers the annealing suppressed excitonic emission and strongly enhanced defect related luminescence bands. Observed post annealed infrared shifts of the PL peaks in the excitonic region are explained assuming a tetragonally distorted GaAs lattice under tensile stress, and an increase in stress after high temperature annealing.

We describe new results observed during resonant excitation in the excitonic region of GaAs grown directly on Si by organometallic vapor phase epitaxy. Two resolved features were found in the light hole photoluminescence (PL) region, one identified with a free exciton process and the other with donor-related transitions. Features which track the laser excitation line were observed and identified with a process in which a donor is excited from the n=l ground state to an n=2 excited state. The PL excitation spectra associated with these features have spectral widths as narrow as 1.5 meV. PL spectral widths of ~3 meV have been attained for the heavy hole exciton band, representing the narrowest value obtained for OMVPE material and an improvement of about 30% over our best previous results.

The strain in MBE GaAs/Si heterostructures grown with a buffer layer are characterized by Raman scattering and luminescence. A graded thickness sample was produced by slowly moving a shutter in front of the sample during the growth. Raman scattering and luminescence measurements made as a function of distance could be related to the strain in the film as a function of film thickness. The measurements showed tensile strain for all thicknesses. The strain in the overlayer was accounted for by the difference in thermal expansion of GaAs and Si. The buffer layer showed the largest tensile strain, and it is proposed that this strain was due to the presence of vacancies.

Residual stress in MOVPE grown GaAs on (100)Si substrates is investigated using Haman spectroscopy, X-ray diffraction, low temperature photoluminescence and photoluminescence excitation spectroscopy experiments. At room temperature, 2 µm-thick GaAs/Si is found to be under biaxial (100) tensile stress of X = 1.8 ± 0.3 kbar, near the epilayer surface. The stress magnitude decreases as the distance from interface decreases. PL and PLE studies on post-growth thermally annealed GaAs/Si reveal coexistence of unstrained and strained GaAs.

This paper reports on strains in epitaxial GaAs layers grown on CaF2/Si(001) and CaF2/Si(111) heteroepitaxial substrates investigated by MeV 4He+; ion channeling. The results indicate that the CaF2 buffer layers reduce strain in the GaAs.

A Transmission Electron Microscopy (TEM) study is presented of GaAs on Si (100) and CdTe on GaAs (100), and the implications for defect nucleation mechanisms are discussed. MOCVD GaAs/Si is shown to grow by island nucleation followed by 3D growth. Single islands are free of inversion domain boundaries (or “APBs”) implying that a single domain is able to grow over a demi-step on the substrate surface during this 3D growth. Misfit dislocations are shown to be edge type during island growth, with 60° type being generated at island junctions. The predominant threading dislocations are found to have inclined a/2 <110> Burgers vectors. The implied mechanisms for the generation of both misfit and threading dislocations are discussed. In MOCVD CdTe/GaAs the microstructure is shown to have a number of qualitatively similar features; in addition, study of this much larger misfit system allows us to deduce a possible explanation for misorientation effects in these systems.

The characterization of semiconductor epilayers by electron microscopy has revealed many different defects in the epilayer. Observations on three representative examples from GaAs epilayers grown on Si are presented. Double-ribbons, which are formed as a result of dislocation interactions near the heterojunction, have been used to determine the intrinsic and extrinsic stacking-fault energies in GaAs. Inverted stacking-fault pyramids have been observed which have nucleated in the epilayer and grown outward to the surface. Finally, differences in the growth rates of different twins are recorded by using AlGaAs layers to preserve the growth surface at various stages during epilayer growth.

One micron thick AlAs/GaAs structures have been deposited by molecular beam epitaxy onto high resistivity silicon substrates. Subsequent to deposition, it is shown that Excimer laser annealing up to 120mJ/cm2 at 248nm improves the GaAs mobility to approximately 2000cm2 /v-s. Dislocation density, however, did not decrease up to 180mJ/cm2 showing that improvement in transport properties may not be accompanied by an associated decrease in dislocation density at the GaAs/Si interface.