Comparison of the GaAs Layers Grown on Porous Si and on Si by Molecular Beam Epitaxy
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COMPARISON OF THE GaAs LAYERS GROWN ON POROUS SI AND ON Si BY MOLECULAR BEAM EPITAXY
B.J. WU, K.L. WANG, Y.J. MI1 AND Y.S. YOON
Device Research Laboratory, Electrical Engineering Department, University of California, Los Angeles, CA 90024 A.T. WU Intel Corporation, Component Research, SC9-45, 2250 Mission College Blvd., Santa Clara, CA 95052 T. GEORGE and E. WEBER Material Science & Mineral Engineering Department, University of California, Berkeley, CA 94720 ABSTRACT
GaAs layers have been successfully grown on tilted (100) Si as well as porous Si substrates by molecular beam epitaxy(MBE). Rapid thermal annealing and vacuum thermal annealing have been used to further improve the quality of the epitaxial layers. We observed that the dislocation density near the interface of the heterostructure is higher for GaAs on Si substrate. Both annealing processes are proven to be useful in improving layer quality, while the vacuum thermal annealing seemed to be more effective in minimizing the residual stress.
INTRODUCTION
Although significant progress has been made in the recent years in the growth of GaAs on Si, the epitaxial layer quality near the interface remains poor. The 4% lattice mismatch and the large difference in thermal expansion coefficients between GaAs and Si are the major causes which result in high dislocation density and large residual thermal stress in the epitaxial layers. Thus the applications of this material to devices are severely limited. Many methods have been proposed to solve these problems; among them, there are two step growth[l], the use of tilted Si substrates[2], (211) substrates[3], and strain layer superlattices[4], etc.. However none of these methods seems to reduce the dislocation density to below 10-8 cm- 2. To have defect-free heteroepitaxy, substrates with patterned seed pads of small dimensions, like porous Si, have been proposed for providing a stressrelieving mechanism[5]. In this work, we studied the crystal quality and stress behavior of GaAs layers grown on Si and porous Si substrates. The effects of rapid thermal annealing (RTA) and vacuum thermal annealing were studied.
Mat. Res. Soc. Symp. Proc. Vol. 145. @1989 Materials Research Society
344
EXPERIMENT We used (100) oriented p+ wafers with 3 degrees tilted toward in this work. Standard sample cleaning procedure was used before the samples were loaded into the MBE chamber. Porous Si substrates were prepared by anodization with constant current in HF solution after the cleaning procedure. Before loaded into MBE system, a thin layer of protection oxide was prepared on every sample by the mixture of HCl, H202 and deionized water. The GaAs layers were grown in a PHI 430 MBE system. Before growth the substrate was heated up to around 8500C with a Ga beam to remove the protection oxide layers. A streaky reflection high energy electron diffraction(RHEED) pattern was obtained after this procedure was completed. The two-step growth method was used in this work. The initial growth of 500A was carried out at 3500C, followed by the
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