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 spectroscopy (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 substrate temperature determination with narrow-band gap epilayers that are sufficiently thick so as to be opaque in the wavelength range corresponding to the substrate band gap. However, we show that by inserting a reflecting layer (or layers) between the substrate and overlying narrow-band gap epilayer, ABES temperature measurements can be carried out in reflection from the backside of the substrate, even in the presence of arbitrarily thick narrow-band gap epilayers. This approach is demonstrated for MBE growth of InAs on GaAs substrates and also for HgCdTe on CdZnTe substrates, and is shown to be accurate to +/-2 degrees C over temperature spans of 300 and 120 degrees C, respectively, for these two material systems in the vicinity of the typical MBE growth temperatures. (C) 1997 American Vacuum Society.