REAL-TIME DIAGNOSTICS OF II-VI MOLECULAR-BEAM EPITAXY BY SPECTRAL ELLIPSOMETRY

Spectral ellipsometry has been applied to in situ diagnostics of Hg1-x CdxTe molecular beam epitaxial growth. Spectral ellipsometry provides surface, composition, and film thickness properties of thin film elect ronic materials in real-time during growth and processing. This study is discussed in two parts. In the first pact, the surface state proper ties of Hg1-xCdxTe and the substrate material Cd1-xZnxTe were studied under ultrahigh vacuum (UHV) conditions. By measuring the spectral ell ipsometric quantities Psi and Delta versus temperature under UHV condi tions, the presence and desorption temperatures of surface species hav e been determined. Tellurium stabilized Cd1-xZnxTe surfaces were not o bserved to exhibit any apparent surface changes during heating under t hese conditions. Oxidized Cd1-xZnxTe surfaces, however, exhibit discon tinuities in Psi and Delta indicative of desorption of a surface speci es in the 300 degrees C range. Tellurium stabilized Hg1-xCdxTe surface s also exhibit discontinuities in Psi and Delta occurring at about 177 degrees C. In the second part of the study, dielectric functions at t he growth temperature, 180 degrees C, were determined for Hg1-xCdxTe a lloys and Cd(0.96)Zn(0.04)4Te. Film compositions were monitored in sit u and in real-time during Hg1-xCdxTe epitaxial growth based on this kn owledge of growth temperature dielectric functions. An experimental an alysis of measurement factors illustrates that compositional sensitivi ty for in situ Hg1-xCdxTe measurement is limited by uncertainties in t he angle and plane of incidence. Simulations show an ultimate multiwav elength sensitivity of significantly better than +/-0.0008 is possible for in situ composition measurements. (C) 1997 American Vacuum Societ y.