Reflectance difference for in-situ characterization of surfaces and epitaxial growth of GaAs on (001) GaAs

Abstract

In spite of the great technical importance of organometallic based epitaxial growth there is still a lack of more detailed understanding of the conditions prevailing on the growing surfaces. This lack of knowledge is in contrast to the case of molecular beam epitaxy (MBE) for which reflection high-energy electron diffraction (RHEED) patterns tell in considerable detail the surface reconstructions which occur in different conditions. With the invention of the reflectance-difference (RD) technique Aspnes opened the possibility for similar control of MOVPE (metalorganic vapour phase epitaxy) growth because the optical techniques do not require high-vacuum conditions as do electron beam experiments. However, there has been, to date, very limited progress in connecting MBE results with MOVPE growth. In this paper we are able to connect (i) the RD results obtained in a growth system (VCE, vacuum chemical epitaxy) where pressure can be varied in the range from low-pressure MOVPE ( mbar) to 1O mbar with (ii) RD and RHEED data obtained from a CBE system (chemical beam epitaxy) where pressure can be varied in the range from iO mbar to 106 mbar. Using this comparison we identify RD features normally seen for VCE and MOVPE conditions with specific surface reconstructions as recognised by RHEED in our CBE system. We then identify the less arsenic-rich surface conditions into which a GaAs surface spontaneously converts when the arsenic source is removed. An identification is proposed for the surface reconstruction conditions which correspond to the critical surface stoichiometry, in terms of the RD response and the material properties, recently demonstrated for VCE growth. Finally, we compare the quality and the character of real-time RD-detected growth oscillations as obtained for CBE, VCE and MOVPE growth.