Photoacoustic measurement of internal quantum efficiency and observation of the exciton effect in GaSe with photoacoustic phase spectra

We studied the room temperature photoacoustic spectra of GaSe single crystals in the vicinity of the energy gap. Exciton formation was observed in both amplitude and phase spectra. The thermal source that arises in the illuminated sample because of optical absorption without free-carrier generation was incorporated in the heat diffusion equation in order to extend the theoretical approach of photoacoustic signal generation. We calculated the optical absorption coefficient, which shows the exciton formation, and the electron-hole generation quantum efficiency η_G using an extended model from the phase and amplitude photoacoustic spectra, respectively. © 1997 Optical Society of America.