ABSTRACT
CuInSe2 (CIS) films have been grown by molecular beam epitaxy, and their intrinsic properties have been extensively investigated. Control of the lattice mismatch between CIS and the substrate by using pseudo lattice-matched substrates made possible the growth of high-quality films from which predominant photoluminescence emissions were observed.
Films grown under Cu-flux excess conditions were found to show significantly better crystalline quality than those grown under In-flux excess conditions; a high density of twins and severe carrier compensation were observed in films grown under an In-excess. A surface Cu2-xSe epitaxial layer was present on the CIS films grown under a Cu-excess. Selective etching of Cu2-xSe by dipping the as-grown films into the KCN aqueous solution indicated that compositions of the CIS films were found slightly less than unity and independent of the Cu and In flux ratio even when grown under Cu-excess conditions; Cu/In ratios of the CIS films are self-limiting and do not exceed unity.
Positron lifetime measurements were carried out to identify the origin of vacancy-type defects. The CIS films grown under a Cu-excess showed p-type conduction and In-rich compositions, and had positron lifetimes similar to those calculated for single vacancy defects, thus the origin of the defects was identified to be Cu-vacancies (Vcu). On the other hand, the measured positron lifetimes of CIS grown under an In-excess were equivalent to the calculated values for divacancies. Airannealing experiments showed that same defect is present in CIS grown under either Cu- or In-excess, and that the positron lifetime decreased by ~20 ps after air annealing, suggesting a defect present in the as-grown films was annihilated by oxygen. Therefore, the origin of the divacancies is attributed to divacancies of Cu and Se (VCu-Se).
