ESR characterization of CuAlSe2 single crystals

High-quality single crystals of CuAlSe2 were grown by the chemical vapor transport technique starting from a polycrystalline CuAlSe2 powder prepared by heating constituent elements above their melting points. The defect states of the crystals were characterized using photoinduced ESR technique at 120 K. An isotropic ESR signal "A" due to a hole trapped by an acceptor was found at the g value of 2.032. The activation energy obtained from the temperature-quenching curve of the A-signal was 40 meV±10 meV. This value was consistent with the level position determined from the difference between the band gap and the peak position of the excitation spectrum of the A-signal. The signal was tentatively assigned to a hole trapped by the Cu vacancy.