We have used high resolution x-ray diffraction to analyze the structural changes that accompany boron doping of silicon by BF3 plasma source ion implantation (PSII). Triple crystal diffraction analysis of as-implanted PSII doped silicon showed little excess x-ray diffuse scattering, even when analyzed using the asymmetric (113) reflection for increased surface sensitivity. This result suggests that PSΠ is capable of providing high dose implantation with low damage. Annealing of the PSII-doped silicon showed the development of a compressive surface layer, indicated by enhanced x-ray scattering directed perpendicular to the surface. Virtually all of the scattering from the annealed samples was concentrated in the so-called “surface streak” which arises due to dynamical diffraction from the perfect crystal Si structure. Little if any diffuse scattering due to kinematic scattering from crystal defects was detected. These observations indicate that plasma source doping can be used to achieve both a shallow implant depth and an extremely uniform incorporation of boron into the silicon lattice.

The stability of GaAs/Si superlattices grown on GaAs substrates using molecular beam epitaxy is described. Typical superlattice structures consisted of ten periods of thin (less than 6.5Å thick) layers of pseudomorphic silicon alternating with thick GaAs layers. We have examined the As2/Ga flux conditions required for the growth of high quality superlattices and have found that the structural perfection is extremely sensitive to the V/III flux ratio. The best superlattices were grown under condition that were just barely enough arsenic to produce a stable (2×4) surface reconstruction in the GaAs layers; increases in the arsenic overpressure resulted in a progressive trend towards 3-D growth of the GaAs on the pseudomorphic Si. In addition, we have examined the stability of GaAs/Si superlattices towards post-growth annealing. Double crystal x-ray diffraction scans showed little change in superlattice structure following rapid thermal anneals at 800°C; at 900°C, however, all but the first order satellite reflections disappeared. We attribute this behavior to the relaxation of pseudomorphic strin and the generation of misfit dislocations at the higher anneal temperature.

In ordering alloy systems, the overall long-range order parameter does not distinguish the degree to which the component structures are delocalized for different configurations of equal randomness. We define a new parameter, which is sensitive to such differences, by considering the short-range order parameters as a set of statistical moments for geometric variation in the crystal. A computer model has been developed which uses this parameter to analyze finite alloy systems for configurational preferences by a Monte Carlo method. Initial studies have established the parametric range as a function of LRO and nonstoichiometry. Qualitative results correspond well to predictions for ideal systems.

The growth of high quality Si/GaAs superlattices on GaAs substrates using molecular beam epitaxy is described. A typical superlattice structure consisted of ten periods of thin (<5Å) layers of pseudomorphic silicon alternating with thick GaAs layers; typical GaAs thicknesses range from 100Å to 1850Å. In situ reflection high energy electron diffraction analysis of the structures during growth showed the silicon layers developed a (3 ×1) reconstruction, while the GaAs exhibited a (4×2)→(3×2)→(3×1)→(2×4) reconstruction sequence. Both observations agree with prior studies of the growth of embedded silicon in GaAs/Si/GaAs heterostructures. X-ray diffraction using the (004) reflection showed sharp and intense satellite peaks (out to 22 orders in one case), indicating a high level of structural quality. Very good agreement has been obtained between observed diffraction patterns and those calculated via dynamical simulation.

Double crystal x-ray rocking curves from single crystal CdTe and CdZnTe of various degrees of crystalline perfection were recorded under diffraction conditions in which the extinction distance varied from under 10 microns to more than 100 microns. In crystals of intermediate quality the rocking curves recorded under conditions of long extinction length showed structure not evident in those recorded under conditions of short extinction length. Integrated reflectivity measurements were performed at both long and short extinction lengths. The results have been interpreted within the framework of a transition from kinematic to dynamical diffraction.

The growth of GaAs on Si by MBE through openings in an oxide or nitride represents a convenient means for achieving monolithic GaAs/Si integration. We have examined a number of the materials growth and processing issues that must be resolved in order to achieve this goal. Some of the specific areas that have been investigated are (a) the effect of trench etching on the morphology of the patterned GaAs; (b) the dependence of patterned feature size on Hall mobility in both as-grown and postgrowth annealed samples; (c) the effect of annealing on the defect structure in the transition region from single crystal GaAs to polycrystalline growth; (d) the dependence of GaAs MESFET performance on proximity to the polycrystal transition; and (e) the performance of Si MOS devices following the GaAs MBE growth. Specific growth and processing issues concerning the integration of GaAs and Si device functions have also been examined.

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.

This paper will review some of the recent progress in GaAs-on-Si devices and circuits, and discuss the issues involved in realizing large scale ICs in GaAs-on-Si wafers. With a recent success in fabricating 1 Kbit static RAMs in GaAs-on-Si wafers, it has become apparent that this material is indeed acceptable for LSI complexity circuits. GaAs MESFETs fabricated using a standard process show an excellent threshold voltage uniformity which is comparable to that for bulk GaAs devices. GaAs bipolar devices on GaAs-on-Si have realized a gain of 25 which is the highest reported for bipolar devices in GaAs-on-Si material. Bipolar ring oscillators and 256-bit ROMs consisting of more than 100 gates have also been realized. In spite of these successes, however, there are numerous issues that need to be solved before this material becomes practical.