Temperature dependence of photoacoustic spectra in CuInSe₂ thin films grown by molecular beam epitaxy

CuInSe₂ (CIS) thin films, the thickness of about 1.0 μm and composition of Cu/In ratio (γ = 1.79), were grown on (0 0 1)-oriented GaAs substrate by molecular beam epitaxy (MBE) at substrate temperature of T_s = 450°C. The samples have been characterized by means of piezoelectric photoacoustic (PPA) measurements between liquid helium (4.2 K) and room temperature (300 K). Two distinct PPA signals due to band gap of CIS and GaAs are observed in the whole temperature range from 4.2 to 300 K and the PPA signals of CIS decrease curvilinearly at the temperature range. Since the PPA signals of CIS thin films can be obtained up to room temperature, the PPA measurements are quite effective to obtain the optical characterizations, especially for the nonradiative recombination processes.