The piezoelectric photoacoustic (PPA) measurements for Cu-rich CuGaSe2(CGS)/GaAs(001) epitaxial layer were carried out between liquid helium and room temperatures. The band gap energies of CGS (A, B, and C bands) were measured to be 1.73, 1.83, and 2.04 eV at liquid nitrogen temperature, respectively. The A band was clearly obtained from 5 to 300 K, and the temperature dependence of the peak energy was fitted with the modified Manoogian–Woolley equation. PPA signals for CGS/GaAs (001) epitaxial layers were obtained between liquid helium and room temperature.

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The piezoelectric photoacoustic (PPA) spectra for Cu-rich CuGaSe2 (CGS)/GaAs epitaxial layers were successfully observed between liquid nitrogen and room temperatures for the first time. Bandgap energy of CGS (A band) is estimated to be 1.72 eV at liquid nitrogen temperature. The activation energies of three possible intrinsic defect levels are estimated to be about 80, 130 and 190 meV.