The Electrical and Optical Properties of GaAs with as Precipitates (GaAs:As)
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THE ELECTRICAL AND OPTICAL PROPERTIES OF GaAs WITH As PRECIPITATES (GaAs:As) A.C. WARREN*, J.M. WOODALL*, J.H. BURROUGHES*, P.D. HEINRICH*, G. ARJAVALINGAM*, N. KIRCHNER*, H.K. KATZENELLENBOGEN*, D. GRISCHKOWSKY*, M.R. MELLOCH**, N. OTSUKA***, K. MAHALINGAM***, F.H. POLLAK****, and X. YIN**** *IBM Research Division, P.O. Box 218, Yorktown Heights, NY 10598 **School of Electrical Engineering, Purdue University, West Layfayette, IN 47907 ***School of Materials Engineering, Purdue University, West Layfayctte, IN 47907 "****Department of Physics, Brooklyn College of CUNY, Brooklyn, NY 11210
ABSTRACT Since its initial report by the IBM/Purdue University group in 1990, GaAs with As precipitates (GaAs:As) has been shown by this group to exhibit unusual and useful electrical and optical properties. In this paper we review our progress in understanding the fundamental properties of this material. We have shown that both the electrical and optical properties of GaAs:As arc explained by assuming that the GaAs is of good crystalline quality and that the As precipitates act as buried Schottky barriers. This model accounts for its semi-insulating stability against both n- and p-type doping, its high-speed photoconductive behavior, and its ability to detect 1.3 micron light when it forms the "I"layer of a PIN photodiode via the internal photoemission process. Using modulation spectroscopy we clarify the fundamental differences between GaAs:As and unannealed GaAs grown at 200 C. We also show that GaAs:As used as a 1.3 micron detector in the metal-semiconductor-metal device structure format, has a photoconductive bandwidth in excess of 50 GHz.
INTRODUCTION GaAs grown at 200-250* C and subsequently annealed at 6000 C has proven valuable in both electronic and optoelectronic applications, but the source of its extremely high resistivity has been the subject of some debate. 1 - 4 A variety of characterization techniques were applied to both the as-grown and annealed layers, with several interesting results. As-grown material (LT-GaAs) was found to 20 be highly strained, containing roughly 1-2% excess As and as high as 10 /cn13 As-antisite defects (by electron paramagnetic resonance (EPR)), 5 ,6 with essentially no photoluminescence response. 7 The balance of the excess As is most likely distributed as interstitials, contributing to the strain. While the excess As
Mat. Res. Soc. Symp. Proc. Vol. 241. 01992 Materials Research Society
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remained after anneal, the strain and point defects were eliminated (to resolution 7 limits), 6 and a fast photoluminescence response could now be observed. The change in material properties upon annealing was not understood until it was found that a substantial fraction of the excess As in the material actually precipitated out into macroscopic As clusters. 6'8, 9 A 6000 C anneal was found to result in irregular precipitates with roughly 6 nm diameter and a volume density 6 of 101 7/cm 3 , which, within experimental error, accounts for all the excess As. .9 This corroborated the observations by EP
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