Experimental photoacoustic observation of the photogenerated excess carrier influence on the thermoelastic response of n-type silicon

Based on the experimental and theoretical signals of an open photoacoustic cell operating with modulation frequencies from 20Hz to 20kHz, a significant contribution of photogenerated excess carriers on the thermal and thermoelastic responses of an n-type silicon plate is observed for the very first time. This is achieved by comparing the measured amplitude and phase of the photoacoustic signal with their corresponding theoretical thermoelastic counterparts, for high enough modulation frequencies mainly. It is shown that the amplitude of the thermoelastic component of plasma-thin samples varies about two orders of magnitude with respect to the corresponding one of plasma-thick samples. Furthermore, we find a maximal temperature difference Delta T=-35nK between the illuminated and non-illuminated sample surfaces, which shows that thin silicon plates with excess carriers could be used as heat sinks.