Carrier concentration dependence of photoacoustic spectra of n-type silicon by microphone and piezoelectric transducer methods

Photoacoustic (PA) spectra near the energy gap (Eg) of n-type silicon (Si) were observed at various carrier concentrations using microphone and piezoe lectric transducer methods. For the microphone method, the PA signal intens ity at energies lower than the Eg increased with increasing carrier concent ration because of the increase in the heat generated in the samples followi ng free carrier absorption and nonradiative relaxation processes. For the p iezoelectric transducer method, the PR signal intensity near energies sligh tly higher than the Eg decreased with increasing carrier concentration beca use of the increase in free electrons at the bottom of the conduction band. The PA spectra were not observed for the samples above a carrier concentra tion of 10(17) cm(-3) due to the suppression of thermoelastic effect by car riers.