SUBSTRATE-TEMPERATURE MEASUREMENT BY ABSORPTION-EDGE SPECTROSCOPY DURING MOLECULAR-BEAM EPITAXY OF NARROW-BAND GAP SEMICONDUCTOR-FILMS

A novel method is described for utilization of absorption-edge spectro scopy (ABES) to monitor the temperature of a semiconducting substrate during molecular beam epitaxy (MBE) of a film with a band gap narrower than that of the substrate. Conventional ABES cannot be used for subs trate temperature determination with narrow-band gap epilayers that ar e sufficiently thick so as to be opaque in the wavelength range corres ponding to the substrate band gap. However, we show that by inserting a reflecting layer (or layers) between the substrate and overlying nar row-band gap epilayer, ABES temperature measurements can be carried ou t in reflection from the backside of the substrate, even in the presen ce of arbitrarily thick narrow-band gap epilayers. This approach is de monstrated for MBE growth of InAs on GaAs substrates and also for HgCd Te on CdZnTe substrates, and is shown to be accurate to +/-2 degrees C over temperature spans of 300 and 120 degrees C, respectively, for th ese two material systems in the vicinity of the typical MBE growth tem peratures. (C) 1997 American Vacuum Society.