High Resistivity GaSb and GaAs Produced by MBE Growth at Elevated Temperatures
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HIGH RESISTIVITY GaSb AND GaAs PRODUCED BY MBE GROWTH AT ELEVATED TEMPERATURES A.Y.POLYAKOV 1 ,A.G.MILNES 1 ,M.STAM 1 ,R.G.WlLSON 2 ,Z.Q.FANG 3 ,P.RAICHOUDHURy 4 ,R.J.HILLARD 4 . 1.ECE Department, Carnegie Mellon University,Pittsburgh,PA 15213-3890,USA 2.Hughes Research Laboratories,250MS RL56,3011 Malibu Canyon Rd.,Malibu, CA 90265,USA 3. Wright State University, Dayton, OH 45435,USA 4. Solid State Measurements,lnc, 110 Technology Drive,Pittsburgh,PA 15275,USA ABSTRACT In this paper we show that when grown by MBE at unusually high temperatures epitaxial layers of GaSb and GaAs are semi-insulating. In GaSb combination of Hall effect, TSC, SIMS and two probe resistivity profiling leads us to believe that high resistivity is due to production of midgap centers at elevated temperatures. No strong evidence of the prevalence of such midgap centers was obtained for high temperature GaAs layers and in this case we believe that high resistivity is associated with the formation of Ga-related precipitates acting as internal Schottky barriers. INTRODUCTION It is now well known that epitaxial layers of some III-V materials (GaAs,AIGaAs) grown by MBE at low temperatures are semi-insulating because of the combined effect of high density of midgap centers and of internal Schottky diodes produced by As inclusions [1-4]. The effect of growth at unconventionally high temperatures is less well studied. In this paper we present the results of such studies for GaAs and GaSb, which are two important Ill-V semiconductors. GaSb is now widely used in combination with AlGaAsSb and InGaAsSb to produce light emitting and light detecting devices for the -21.Lm wavelength range [5-7]. For some of these devices (e.g. p-i-n photodiodes) it is important to be able to obtain GaSb with low carrier concentration. However, in undoped GaSb conductivity is controlled by VSb-related intrinsic acceptors with concentration in the 10 16 -10 17 cm- 3 range [8,9]. Hence it is extemely difficult to grow GaSb of either n- or p-type with carrier concentrations below -1015-1016 cm- 3 . In what follows we show that by MBE growth at temperature in excess of 600 0 C it is possible to prepare GaSb layers with the carrier density close to intrinsic. For GaAs we will demonstrate that high temperature (-7000 C) MBE growth can produce material with resistivity -105Ohm*cm and that possibly this material has such properties because of the presence of Ga-related precipitates. EXPERIMENTAL The samples studied in this work were grown by MBE in a Perkin Elmer 400 sys-
Mat. Res. Soc. Symp. Proc. Vol. 262. @1992 Materials Research Society
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tem. GaSb layers were grown either on (100) GaSb substrates or on (100) GaAs semi-insulating (SI) substrates. GaAs films were grown on conductive n-type (n10 17 cm- 3 ) or on undoped SI-GaAs substrates. The GaSb wafers were polished and etched in Br/methanol and the GaAs substrates were etched in H2 SO 4 :H2 0 2 : H2 0. Usually MBE growths of GaSb in our system are made at 5000C with oxide removal at 5600C (600 0 C for GaAs substrates)
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