Size effects on photoacoustic spectra for GaAs fine powder

The photoacoustic (PA) spectra of GaAs fine powder whose particle size was of the micrometer order were measured. The PA spectra show a broad peak and this peak shifts to the high-energy region as the sample particle size decreases. The band gap shift can be observed for the large-particle-size samples in the PA spectra. On the other hand, the PA peak shift for the small-particle samples is caused by the light penetration effect causing the decrease of the PA signals, where the particle size is smaller than the light absorption length. Although careful elucidation of the band gap shift in the fine powder samples from the PA measurement is required, the light absorption spectra above the band gap energy can be estimated.