To clarify the mechanism of the dip and hump during the photoquenching process observed in the time-dependent piezoelectric photoacoustic (PPA) signal, the PPA spectra were measured by changing the illumination time of the quenching-light of 1.12 eV at 80 K. It was found that a distinctive peak appeared around 1.1 eV and moved to higher photon energy side with increasing the illumination time. A contribution of the deep level that changes the activation energy during the photoquenching process is considered.