Rheed Intensity Observation of AIAs and GaAs by In Situ Etching Using Arsenic Tribromide
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ABSTRACT The first in situ layer-by-layer etching of AlAs(100) surfaces has been observed by using RHEED intensity oscillations technique and is contrasted with the results obtained for the etching of GaAs(100). The experiments were conducted by introducing the etchant, arsenic tribromide, directly into a conventional MBE chamber without the use of any carrier gas. RHEED intensity oscillations during the etching of AlAs are observed between 350 and 760'C indicating a continuous increase in the etching rate with temperatures, with no supply rate limiting conditions being reached. Conversely, oscillations from GaAs reveal a reaction rate limited region at low temperatures (=•500°C) and a supply rate limited region at higher temperature(>500'C). The maximum selectivity in the etching rates between GaAs and AlAs is obtained at 450'C (40:1). The selectivity , and the ability to monitor the layer-by-layer process by RHEED intensity oscillations is foreseen to be of great importance for more controlled fabrications of AlAs and GaAs heterointerfaces. INTRODUCTION The recent interest in fabricating mesoscopic structures on patterned substrates demands in situ processing techniques with atomic control. Most of the techniques which have been developed so far is based on the growth processes such as molecular beam epitaxy (MBE), chemical beam epitaxy (CBE) and atomic layer epitaxy (ALE). These processes are successfully controlled using the RHEED intensity oscillations technique based on a layer-by-layer mode. Recently, RHEED intensity oscillations have been observed during the etching of GaAs using molecular beams of arsenic tricloride (AsCI3) [1,2], arsenic tribromide (AsBr3) [3] and tris-dimethylaminoarsenic (TDMAAs) [41 on GaAs(100) surfaces. This in situ etching occurs via a layer -by-layer mechanism analogous to the reverse process of growth and enables control on the atomic scale. A combination of this in situ etching and growth within the same ultra high vacuum (UHV) chamber offers considerable potential for the fabrication of novel low dimensional structures. In this paper, we report the first observation of RHEED intensity oscillations for the etching of AlAs(100) with AsBr3 in a modified MBE growth chamber equipped with an additional gas manifold. The oscillations are observed over a wide temperature range 350-760'C and the variations of etching rate (at constant etchant supply) suggest that this process is reaction rate limited throughout this temperature range. The etching rate of AlAs is found to be less than that of GaAs at all temperatures, where oscillations from GaAs show a high temperature supply rate limited region being distinguished from a low temperature reaction rate limited region. EXPERIMENT The experiments were carried out in a modified conventional solid source MBE system equipped with a gas manifold, a growth-vent switching system and an additional turbo molecular 67 Mat. Res. Soc. Symp. Proc. Vol. 405 01996 Materials Research Society
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