Response times of ∼60 and 25 ps (FWHM), respectively, have been measured for photoconductive detectors fabricated in GaAs layers grown by molecular beam epitaxy on silicon substrates and silicon-on-sapphire substrates. Photoconductive detectors, which can be readily combined with GaAs logic devices such as MESFETs to provide high-speed optical to electrical conversion, could be used in optical interconnects that are integrated with Si circuits on monolithic GaAs/Si wafers. Transconductance values of 120 mS/mm have been obtained for MESFET's fabricated in GaAs layers grown on silicon-on-sapphire substrates.

We report the synthesis, structural characterization, and preliminary optical studies of ultrathin Ge-Si superlattices with individual sublayers smaller than the Si unit cell, grown by MBE on (001) silicon substrates. Structures are fabricated one monolayer at a time in a configuration GeGeSiSiGeGe..., resulting in either ordered alloys or complex cell superlattices. Rutherford backscattering and channeling experiments on these highly strained heterostructures indicate excellent crystallinity with tetragonal distortion as high as 3.5%. Electron diffraction patterns exhibit characteristic superlattice reflections indicative of one-dimensional layering with periodicity of four monolayers. X-ray scans along the growth direction at the (002) position in reciprocal space reveal a strong peak not observed in random GeSi alloys. This scattering is attributed indirectly to the GeSi ordered phase. The optical transition energies measured by Schottky barrier electroreflectance correspond to those expected from homogeneous alloys of the same composition; however, the width of optical transitions is less than 30 meV at room temperature, allowing a clear resolution of the splitting of the valence band by strain. Modification of the unit cell of the diamond lattice in this way should permit the design of materials with novel opto-electronic characteristics. Preliminary Raman and photoconductivity measurements are also reported.

A high-volume epitaxial reactor has been used to investigate the feasibility for the production growth of GaAs on silicon substrates. The reactor is a customized system which has a maximum capacity of 39 three-inch diameter wafers and can accommodate substrates as large as eight inches in diameter. The MOCVD material growth technique was used to grow GaAs directly on p-type, (100) silicon substrates, three and five inches in diameter. The GaAs surfaces were textured with antiphase boundaries. Double-cyrstal rocking curve measurements showed single-cyrstal GaAs with an average FWHMof 520 arc seconds measured at four points over the wafer surface. Within-wafer thickness uniformity was ± 4% with a wafer-to-wafer uniformity of ± 2%. Photoluminescence spectra showed Tour peaks at 1.500, 1.483, 1.464, and 1.440 ev. Schottky diodes were fabricated on the GaAs on silicon material.

The photoluminescence of GaAs/Si grown by OMCVD has been analyzed as a function of temperature and the dominant high temperature line identified as a conduction-band-to-valence-band transition. Photoluminescence excitation spectra indicate that the transition is excitonic at 4.2 K. A second line, also identified as intrinsic, dominates the spectra below 100 K. A biaxial tensile strain is proposed to account for the two intrinsic lines through a splitting of the valence band degeneracy.

This paper reviews the “template” growth technique in UHV and the novel structures and properties of single crystal silicide thin films and double heterostructures.

Electron tunneling spectroscopy experiments have been performed on single-crystal epitaxial silicide films grown on (111)-oriented (off 4 °) Si:As. 250 Å-thick films of CoSi2, and type-A and -B NiSi2 on degenerate substrates (Nd = 2 × 1019 cm−3) have been studied. All spectra show forward bias peaks at energies corresponding to k-conserving bulk Si phonons while in reverse bias only the Si TA phonon is observed for NiSi2 /Si structures. Plots of dV/dI vs. V for CoSi2 /Si structures yield maxima at a forward bias of 39meV, indicating an enhancement in n-type dopant concentration within ˜ 100 Å or more of the silicide-silicon interface.

Transition metal silicides are now being used as essential and integral elements of microelectronics technology. Epitaxial growth and deposition provide additional flexibility for many device and circuit applications.

In this paper, various epitaxial growth techniques, namely solid phase epitaxy and molecular beam epitaxy are reviewed. The resulting morphology, crystallinity, and Schottky barrier heights as well as deep-level defects are contrasted. The parallel and perpendicular strains as a function of film thickness is reported.

Application of the epitaxial silicide in improving conventional integrated circuits as well as in fabricating new devices are discussed.

The two major issues in the growth of a heterostructure are (1) the degree of perfection of the overlayer and (2) the sharpness of the interface. The initial stages of interface formation play a crucial role in this respect. Relevant questions are addressed under atomically clean conditions in the Si/Ge Si/Si and Ge/Sn systems, using ion scattering surface analysis, low energy electron diffraction and Auger electron spectroscopy. Of particular interest with respect to (1) is the general role of reconstruction in epitaxial growth: A necessary condition for perfect growth is the reordering of the substrate surface reconstruction. We show that the deposition temperature necessary to achieve this reordering depends strongly on the topography of the substrate reconstruction. For example, Ge deposition at room-temperature reorders the Si(100)2×1 reconstruction but not the Si(111)7×7, implying different epitaxial temperatures for these two substrates. To illustrate (2) we discuss the complex growth and anomalous diffusion found in the Ge/Sn system. Below a certain critical coverage Θc (1.15·1015 cm−2) no indiffusion of the Sn overlayer takes place, even at 700 K, although above Θc severe indiffusion does occur at this temperature. This result is discussed in terms of theories of surface segregation.

Germanium films have been epitaxially crystallized on silicon substrates using the electron-beam evaporation technique and the laser! strip-heater recrystallization technique. Epitaxy was achieved either directly on Si surfaces or laterally on oxide/nitride-coated Si wafers. Evaporated Ge epi-layers were mirror-smooth and were found to be in excellent crystal quality. The recrystallized Ge on Si were also found to be good crystal, but showed somewhat roughened surface morphology. In both cases, the Ge near the Ge/Si interface is heavily replete with misfit dislocations arising from 4% lattice mismatch between Ge and Si. The recrystallized Ge on insulator (GOI) showed no mismatch dislocations at the Ge/insulator interface but developed voids arising from Ge dewetting from the insulator surface. Twins have been observed to be the most prominent defects in recrystallized Ge, whether seeded or unseeded. The objective of this study is to achieve quality Ge layers that can be used as intermediate template to accomodate GaAs on Si.