Advanced III-V materials processing in the vacuum of space

GaAs films, both silicon doped and undoped, have been deposited by Molecular Beam Epitaxy (MBE) in Low Earth Orbit (LEO) in an ultra vacuum environment created by the Wake Shield Facility (WSF). The WSF is a 12 foot diameter stainless steel disk that sweeps out a volume of space thus creating an ultra vacuum in its wake. It was developed specifically to take advantage of the ultra vacuum for the deposition of thin film materials. The WSF was flown for the first time on STS-60 in February, 1994. The mission objectives were to measure the unique wake vacuum environment formed by the Wake Shield, and to epitaxially deposit GaAs thin films. In this paper we describe the films deposited and report on the characterization performed to date. Films were deposited in two basic structures. The first structure consisted of undoped GaAs films of thicknesses ranging from 2 to 4 /spl mu/m with a thin (/spl ap/200 mn) highly silicon doped layer (n/spl ap/5/spl times/10/sup 17//cc) on top. This is basically a metal-semiconductor field effect transistor (MESFET) structure. The second structure was a lightly silicon doped GaAs film (n/spl ap/5/spl times/10/sup 15//cc). We have obtained Photoluminescence (PL), Secondary Ion Mass Spectrometry (SIMS) and X-Ray diffraction data on selected films. The data indicate nominal quality single crystal films with oxygen and carbon contamination. The source of the contamination and further characterization are discussed.