Metalorganic vapor phase epitaxy of Cu(Al xGa 1− x)(S ySe 1− y) 2 chalcopyrite semiconductors and their band offsets

Abstract

Cu-chalcopyrite (Ch) Cu(Al,Ga,In)(S,Se) 2 compounds and alloys were grown epitaxialy on various substrates by low-pressure metalorganic vapor phase epitaxy. They grew in such a manner that the lattice mismatch between the epilayer and the substrate became minimum. Growth of anion and cation alloys revealed that the vapor pressure of Al–S reactants is much higher than that of Ga–S or Al–Se ones. Most of residual strain in the epilayer was assigned as being due to the pseudomorphic stress for those having small lattice mismatch (<1%) against the substrate and to the thermal stress for large lattice mismatch (>1%) ones, and the strain problem was solved by the use of Ch structure substrate. All single-domain compound epilayers, namely CuAlS 2, CuAlSe 2, CuGaS 2, CuGaSe 2, CuInSe 2, and their alloys exhibited predominant excitonic photoluminescence peaks. A noticeable excitonic feature was found in the PL spectra of CuAlS 2, CuGaS 2 and CuGaSe 2 even at 300 K. Band diagram of Cu(Al,Ga)(S,Se) 2 system was discussed, and they are considered to offer the TYPE-I heterostructures between the corresponding narrow bandgap materials and wide bandgap ones.