Quantitative Deconvolution of Photomodulated Thermoreflectance Signals from Si and Ge Semiconducting Samples

Abstract

A variety of photomodulated thermoreflectance (PMTR) data have been obtained for two germanium wafer samples (one crystalline and the other ion-implanted and unannealed), and three silicon wafer samples (one crystalline, unimplanted; the other implanted and flash-annealed; and the third an amorphous thin layer). Physically different mechanisms contributing to the PMTR signals have been formulated theoretically for these materials. For the crystalline and implanted-annealed samples it was found that the PMTR signal has two main components, one due to temperature modulation (thermal wave); the other due to the free-carrier density modulation (the Drude effect). For the ion-implanted-unannealed and amorphous materials two components were found to be dominant: one due to the thermal wave; the other due to the band-filling of localized gap states. The two component mechanisms were validated in a quantitative manner by curve-fitting experimental PMTR frequency-response data, while taking into account the photocurrent (PC) responses of the samples. As a result, unambiguous deconvolution of the electron-hole plasma or trapped-carrier contribution and the thermal-wave component to the PMTR signal were obtained throughout the frequency range 1 kHz–1.6 MHz.