The Growth, Characterization and Electronic Device Applications of GaAs/Si
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THE GROWTH, CHARACTERIZATION AND ELECTRONIC DEVICE APPLICATIONS OF GaAs/Si
A. S. JORDAN, S. J. PEARTON, and W. S. HOBSON AT&T Bell Laboratories, Murray Hill, New Jersey 07974 ABSTRACT We review the growth of GaAs on Si by MO-CVD and MBE and discuss the relative merits of these techniques. Major emphasis is placed on the structural and optical characterization of the material that may be indicative of device performance. Typical GaAs layers on Si are free of antiphase domains and the crystallinity at the surface for a 3-41tm thick deposit approaches that of bulk GaAs, as evidenced by the RBS backscattering yields and Si ion implantation profiles. The major 9 2 drawbacks of GaAs heteroepitaxy on Si are the very large dislocation densities (106 - 10 cm- ), 4 3 the relatively high unintentional doping concentration (>5 x 101 cm- ) that is partly attributable to Si outdiffusion, and the excessive bowing due to thermal expansion coefficient mismatch. While there are growth and processing techniques to overcome bowing or at least its influence, dislocations and low resistivity are hard to remedy. We discuss novel schemes to reduce dislocations (selective area growth, superlattices and thermal cycling) and efforts to improve the electrical properties (doping, optimization of V/III ratio). A variety of electronic devices and circuits have been fabricated using GaAs/Si. We shall present results on MESFETs, HBTs and HFETs processed in our laboratory and elsewhere. It is quite encouraging that HFETs with a transconductance of 220mS/mm are achievable. However, lasers in room temperature CW operation still have a very limited lifetime. Finally, we discuss the implications of GaAs/Si for a broader area of mismatched heteroepitaxy (InP/Si, InP/GaAs, etc.) and speculate on the future prospects for this new materials technology. I. INTRODUCTION In the last few years considerable scientific and engineering resources have been devoted worldwide to the heteroepitaxial growth of GaAs on Si. Besides GaAs device applications, this technology may lead to the monolithic integration of GaAs and Si circuits as well as fast optical chip-to-chip interconnects. Significant progress has been made already on both the material and device fronts. But, perhaps the most important effect of all the efforts in GaAs on Si is the knowledge gained in heteroepitaxial growth that is applicable to a broader class of mismatched semiconductor materials. To a large extent, future advances in optoelectronics depend on the materials preparation and device processing capabilities of mismatched systems. The arguments in favor of GaAs on Si heteroepitaxy are by now all familiar() and here deserve only a brief recapitulation. The major advantage is the replacement of GaAs wafers by low cost, large diameter Si substrates in GaAs electronic devices and circuits. At the same time, the higher mechanical strength and size of Si makes the processing of GaAs circuits compatible with the highly developed Si technology. Further obvious advantages are the higher thermal conduc
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