Detailed absorption analysis from photoacoustic measurements of post-annealed CuInSe2 in various environments

Abstract

In this paper, we analyze the optical absorption properties of CuInSe2 single crystals in the photon energy range 0.8 to 1.1 eV from measurements carried out at ambient temperature using the photoacoustic spectroscopy technique following post-annealing processes at the temperature range 100 to 300 °C for a period of time of 30 min in various environments (vacuum, air and neutral). These are usually the most used media for thermal treatment. As-prepared thin films semiconductor materials usually require post-annealing in order to improve their structure and morphology to enhance their electronic properties. Despite the low temperatures and short period of the process, post-annealing is shown that it has an important impact on the absorption spectral behaviour of the compound. The potential of photoacoustic depth profiling operational mode carried out at two modulating frequencies (112 and 185 Hz) has been used to check on the samples’ homogeneity in respect to depth defect populations distributions. A shift by 65 meV in the upper limit of the absorption coefficient spectrum due to a higher inter-band transition has been observed following the processes of post-annealing in air and in vacuum, whereas the process when carried out in a neutral environment the samples keep their band edge as prior to the treatment.