Reflectance-difference studies of organometallic chemical-vapor-deposition growth transients on (001) GaAs

Abstract

We report the first real-time, in situ spectroscopic measurement of a semiconductor surface [(001) GaAs] during crystal growth by organometallic chemical vapor deposition (OMCVD). Reflectance-difference spectroscopy (RDS) is used to enhance the ordinarily low sensitivity of optical measurements to surface effects and thereby to obtain information about the state of the surface for various sample temperatures and ambient conditions during OMCVD growth. The maximum reflectance-difference (RD) signals that we observe fall in the same 2–3 eV energy range as those seen in molecular beam epitaxy (MBE). This suggests that RD measurements can be used to follow relative surface coverages of Ga and As in OMCVD as well as in MBE. Time- and temperature-dependent studies show that this maximum signal closely follows the kinetics of the last rate-limiting step in the decomposition of trimethylgallium (TMG), thereby confirming its sensitivity to surface chemistry (relative coverage of As and Ga.) Using this signal, we follow changes of the OMCVD (001) GaAs growth surface with ambient composition and growth history as well as substrate temperature. Our results indicate that RDS will be very useful in providing insights into, and real-time measurement and control of, crystal growth by OMCVD.