INSITU MONITORING OF CRYSTAL-GROWTH BY REFLECTANCE DIFFERENCE SPECTROSCOPY

Reflectance difference spectroscopy (RDS) is a surface analysis technique that was invented in 1985 by Aspnes. Here, we give a summary of its application to crystal growth techniques which gave new and valuable real time information about the growth process. Also, this information was obtained in-situ, in molecular beam epitaxy (MBE) and organometallic chemical vapor deposition (OMCVD) crystal growing setups which are routinely used to produce high quality device structures. The application of RDS to OMCVD allowed us to develop a "textbook" like model of growth kinetics, which includes two independent microscopic mechanisms, i.e. adsorption (at - 26 kcal/mol) of the reacting molecule (trimethylgallium (TMG) in the case of GaAs), followed by its decomposition (at 39 kcal/mol) on the growing GaAs surface. Our model includes an effect called steric hindrance, associated with the large size of the TMG molecule. This study represents the first direct quantitative evaluation of the catalytic effect of the GaAs surface for the decomposition of TMG. We discuss implications of the model both for growth in the ALE mode as well as for conventional OMCVD growth and comment on the relative importance of surface and gas phase reactions. The application of RDS to MBE revealed remarkable details about the complex intermediate steps that surfaces undergo during growth and enabled to extract directly surface dielectric functions. Finally, applications of the technique as well as results obtained in a number of laboratories where RDS is currently being developed are discussed.