Visible and Ultraviolet Photoluminescence from Cu–III–VI2 Chalcopyrite Semiconductors Grown by Metalorganic Vapor Phase Epitaxy

We optimized the overall process of heteroepitaxial growth of wide-gap Cu–III–VI2 chalcopyrite semiconductors by using the low-pressure metalorganic vapor phase epitaxy technique, and obtained very high quality epilayers of them. All end-point compounds, namely CuGaSe2, CuGaS2, CuAlSe2 and CuAlS2, exhibited predominant free and bound excitonic photoluminescence (PL) peaks at low temperature. The color of the emission varied from red to ultraviolet. The room temperature (RT) PL spectra exhibited predominant near-band-edge emission except for that for CuAlSe2. A noticeable excitonic feature was found in the PL spectra for CuAlS2 and CuGaS2 even at RT. Time-resolved and excitation intensity-dependent PL measurements revealed the existence of free-to-bound (FB) and donor-acceptor pair recombination emission centers in some undoped and impurity-doped compounds and alloys. The ionization energy of the recombination centers increased with increasing band gap energy of the matrix, reflecting an increase in the hole effective mass. The potential of heteroepitaxial layers of chalcopyrite semiconductors as new light-emitting materials was demonstrated.