Epitaxial GaAs on Si: Progress and Potential Applications
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EPITAXIAL GaAs ON Si: PROGRESS AND POTENTIAL APPLICATIONS DON W. SHAW Materials Science Laboratory Texas Instruments Incorporated P.O. Box 655936, MS-147 Dallas, TX 75265
ABSTRACT Recent successes, such as the demonstration of a iK SRAM, have established epitaxial GaAs on Si substrates as a promising technology rather than a device designer's dream. For the first time we can seriously consider combining the individual electronic and optical properties of GaAs and Si within a single epitaxial structure. Applications for GaAs on Si range from those that simply utilize the Si as a low-cost, large-area passive substrate with superior strength and thermal conductivity to the long-sought multifunction integrated circuits where Si and III-V components are integrated within a single monolithic chip. This paper will attempt to provide a realistic appraisal of the potential applications of epitaxial GaAs on Si with emphasis on the special demands imposed by each application and barriers that must be circumvented. INTRODUCTION For mary years the desirability of epitaxially depositing GaAs on silicon substrates has been recognized. The absence of success in experimental attempts was not unexpected because of the large (4%) lattice mismatch between GaAs and Si. However, research progress made during the past
three
years
is
imposing
a
significant
change
in
our
outlook
for
heteroepitaxy with mismatched systems. Although GaAs on Si is the subject of much of this research, the successful concepts should be applicable to other epitaxial materials combinations that previously were considered infeasible. New mismatched, multimaterial systems offer exciting applications and should spur intensive efforts in this area during the next few years. The achievement of device-quality GaAs on Si after many years of failure is attributable to several factors. Molecular beam epitaxy with its sophisticated instrumentation and ultrahigh vacuum environment permitted preparation of oxide-free silicon surfaces. It also offered low temperature depositions, free of detrimental chemical interactions. This resulted in successful surface preparation procedures, but the lattice mismatch and associated misfit dislocations remained. Soon it was found that by appropriate choice of substrate crystallographic orientation and intermediate layer deposition regime most of the misfit dislocations could be confined to a thin region near the interface. As a result the thicker portions of the epitaxial structure could have a Crystal perfection that, though inferior to homoepitaxial GaAs on GaAs substrates, was suitable for acceptable device
performance.
The technology has since appeared increasingly promising with
the demonstrations of GaAs-on-Si device performances comparable to those from conventional GaAs epitaxial and bulk structures. Now we approach the stage of sober realization that epitaxial GaAs on Si may be a manufacturable technology. Which of the many applications that have
Mat Res. Soc. Symp. Proc. Vol. 91
1987 Materials Research Society
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