Two-layer model for photomodulated thermoreflectance of semiconductor wafers

A complete theoretical analysis of the laser photomodulated thermoreflectance signal from a two-layer semiconducting wafer is presented. It is shown that the electronic and thermal properties of a thin surface layer may be determined by using the measured induced photothermal signal. Several numerical simulations are performed in order to study the influence of various electronic, optical and thermal parameters of the two-layer sample on the photomodulated thermoreflectance signal. The influence of the upper layer as well as the influence of the substrate on the signal are also discussed and parameter regimes are identified, where the characterization of the thin overlayer may be possible using this technique.