Characteristics of Si-Implanted (211) Versus (100) GaAs
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CHARACTERISTICS OF Si-IMPLANTED (211) VERSUS (100)
GaAs
J. EPP, J. G. DILLARD, A. SIOCHI, R. ZALLEN, E. D. COLE, S. SEN, A. VASEASHTA, AND L. C. BURTON Virginia Polytechnic Institute & State University, Blacksburg, VA 24061, USA ABSTRACT Raman and XPS measurements were made on SI-implanted Transport, (1.7x10 1 3 cm- 2 , 50keV) and rapid-thermal annealed (100) and (211) GaAs substrates In an effort to distinguish differences between the two orientations. The no significant differences were found. With these techniques, implant-damage depth was about 1200A for both orientations, with slightly No higher near-surface damage (and lower mobility) apparent for (211). unusual features in the (211) carrier concentration profile, as was previously reported, were evident. INTRODUCTION (100) is the traditional substrate For Si-implanted GaAs MESFETs, orientation. It has recently been reported, however, that using the (211) Unusual non-Gaussian carrier orientation results in better devices [1]. concentration profiles, with a natural n+ surface region, were obtained. Higher transconductances and lower noise figures resulted for devices made on (211) substrates. In this paper we report measurements aimed at discerning differences between certain materials related properties for Si-implanted (100) and (211) GaAs substrates. EXPERIMENTS with GaAs substrates were Implanted (100) and (211)-oriented Rapid thermal anneals were 1.7x10 1 3 cm- 2 of Si ions at 50 keV energy. performed with silicon nitride caps which were subsequently removed. 0 0 0 Annealing conditions were: none; 750 C, 850 C and 950 C for 30 sec. Specific will be noted below where appropriate. annealing conditions For electrical measurements, ohmic contacts in the van der Pauw configuration were prepared by depositing 88:12 Au:Ge, plus a Ni cap, and annealing at 440 0 C in forming gas. A four-stripe conductor arrangement was Electrical and optical profiles used for the photoconductivity measurements. 1: 1: 100 after sequential etches using a were made by measuring H2 SO 4 :H 2 02 :H 2 0 etch, which removes GaAs at a rate of approximately 600A Raman measurements were made in the backscatter configuration min-1 [2,31. with a laser wavelength of 4579A. XPS measurements were made on a Perkin Elmer Model 5300 instrument. RESULTS AND DISCUSSION Carrier concentration and mobility profiles for the implanted and annealed Such profiles are shown in (100) and (211) orientations are very similar. The only discernible difference is Figures 1 and 2, for the 850"C anneal. With respect to slightly lower mobility values for (211) near the surface. carrier concentration profiles, the very flat profile for (211) between 200A and 1000A, with a sharp increase in carrier concentration within 200A of the Carrier surface, as reported by Banerjee et al. [1), was not found. concentration and mobility profiles for the three annealing temperatures were almost identical.
Mat. Ras. Soc. Symp. Proc. Vol.128. 01989Materials Research Society
678
2E18 A(211)
o (100)
1E18
00 0
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