Heteroepitaxy and Characterisation Of Ge-Rich SiGe Alloys on GaAs
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Heteroepitaxy and Characterisation Of Ge-Rich SiGe Alloys on GaAs
R. Venkatasubramanian, M.L. Timmons and M. Mantini, Research Triangle Institute, Research Triangle Park, NC 27709; C.T. Kao and N.I. Parikh, Dept. of Physics and Astronomy, UNC, Chapel Hill, NC 27599.
Abstract: Growth of SiGe alloys on GaAs substrates at temperatures as low as 590 °C is described. The growth has been accomplished using the pyrolysis of disilane (Si 2 H6 ) and Germane (GeH 4) at such temperatures. The layers were characterized electrically and show n-type conduction with a carrier concentration of -' 1 x 1018 cm-3. The high quality of the SiGe layers are evident in the Rutherford backscattering (RBS) channeling results on SiGe/GaAs structures. A Xmin of 5.6% has been obtained for a Si0.05 Ge 0 .g5 layer on GaAs. Xmin increases with increasing silicon content in the SiGe layers. The SiGe alloy layers were studied by x-ray diffraction, and the composition was determined assuming coherent, but tetragonally-distorted growth of SiGe on GaAs. The distortion calculations, based on theoretical elastic-constants, were confirmed using Auger electron spectroscopy to check alloy composition.
INTRODUCTION Si-rich SiGe alloys are receiving considerable attention for silicon-based heterojunction device applications [1]. Ge-rich SiGe alloys, on the other hand, are also useful semiconductors for a number of applications such as photodetectors for light-wave communication that can be integrated with GaAs-substrate based high-speed electronics. They are also useful for GaAs-based heterojunction device applications similar to the recently studied AIGaAs/Ge/GaAs heterojunction bipolar transistors [2]. Ge-rich SiGe alloys also offer optimum bandgaps as components of multijunction solar cells. In contrast to Si-rich SiGe alloys, there has been limited study of Ge-rich SiGe alloys with regard to their growth and properties [3,4]. In one study [3], the SiGe alloys were deposited on Ge substrates using the thermal decomposition of silane (Si H 4) and GeH 4 at temperatures as high as 850 C. Even at these temperatures the growth was poor. However, at growth temperatures of - 900° C, good quality epitaxy of Ge-rich SiGe layers on Ge has been obtained using the pyrolysis of Si 2H6 and GeH 4 [4]. A key for the SiGe/GaAs heterojunction device-applications is the low temperature growth of SiGe alloys on GaAs to avoid problems related to the decomposition of GaAs. In this paper, we discuss the growth of these alloys on GaAs at temperatures as low as 590 °C using the pyrolysis of Si 2H6 and GeH 4 . We have also studied the structural and electrical
Mat. Res. Soc. Symp. Proc. Vol. 198. 01990 Materials Research Society
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propoerties of these layers, using x-ray diffraction, RBS channeling, Auger electron spectroscopy and spreading-resistance measurements.
EXPERIMENTAL Growth of SiGe layers was carried out in a horizontal-flow, atmosphericpressure epitaxial reactor with an rf-heated graphite susceptor, which is coated with pyrolytic boron nitride. GaAs substrate
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