Anion vacancies in CuInSe₂

Effects of the Cu_2-xSe surface phase, the post-growth air-annealing and the Na incorporation on the growth and properties of CuInSe₂ films have been systematically investigated by various defect-sensitive characterization techniques such as low temperature photoluminescence and positron annihilation. The presence of the Cu-Se surface phase, the post-growth air-annealing and the Na incorporation all provided significant changes in photoluminescence spectra. Decrease in positron lifetime and reduction of twin density were found to occur simultaneously, along with the changes in photoluminescence spectra. Change in photoluminescence spectra and the corresponding decrease in positron lifetime indicate the annihilation of Se-vacancies; the control of Se-vacancy is a key issue to be addressed for improving the electrical, optical and structural properties of CuInSe₂ films.