Thermoreflectance in Semiconductors

The thermoreflectance spectra of Si, AlSb, GaP, GaAs, GaSb, InP, InAs, InSb, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgSe, and HgTe are reported. Measurements were made on most materials at both room and liquid-nitrogen temperatures. The positions of the peaks observed are compared with previous reflectance and electroreflectance data. Some representative spectra were subjected to a Kramers-Kronig analysis, and the changes in the real and imaginary parts of the dielectric constant, induced by the change in temperature of the sample, were obtained. The resulting line shapes are compared with those derived from elementary theory. In order to achieve reasonable agreement between theory and experiment, it is found necessary to invoke the presence of excitons at all the interband edges. It is demonstrated that, under certain conditions, the type of critical point involved in the transition can be identified.