RHEED Oscillations Control of GaAs and AlAs MBE Growth Using Phase-Lock Modulated Beams
Since the origin of MBE, when Cho had the insight of adding a RHEED set-up to his UHV epitaxy system, this technique remains as the most useful and extended in-situ characterization tool. Recording of the oscillations of the RHEED specular beam intensity is an invaluable further development which allows to follow the MBE growth process monolayer by monolayer. This growth process has been shown by using RHEED, to be a competition of growth mechanisms such as two dimensional (2D) growth and terrace propagation. Only the 2D component is the origin of the observed oscillations. Recently we interpreted the general phenomenon of RHEED oscillations damping based on experiments showing that oscillations can be maintained indefinitely during GaAs and Alx Ga1-x As growth by periodical short interruptions of the As4 beam in phase with the monolayer by monolayer growth sequence. In doing so, good quality and excellent morphology layers can be grown, even at low substrate temperatures. An extreme way of modulating the beams in synchronism with the 2D growth cycle is to alternate the arrival of Ga and As4 beams to the growing surface. This method, which has been used very successfully by Y. Horikoshi and designated Migration Enhanced Epitaxy, is apparently similar to Atomic Layer Epitaxy (ALE).
KeywordsSurface Migration Atomic Layer Epitaxy Monolayer Growth Oval Defect Hall Carrier Concentration
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