Defect Properties of CuInSe2 Single Crystals Prepared by Selenization Horizontal Bridgman Method

Abstract

CuInSe2 bulk single crystals have been grown using the selenization horizontal Bridgman method. On the basis of the temperature variation of Hall coefficient curves, we have classified the p-type CuInSe2 into the deep (D), shallow (S) or a combination of both (B) types, and identified that the activation energies of acceptors are 50–60 meV for In vacancies and 10–20 meV for Cu vacancies and Cu's in the In site. The donors, whose densities decrease with annealing in Se atmosphere, are ascribed to Se vacancies having an activation energy of 10 meV. The optical band gaps of the D- and B-type samples are estimated to be 1.04 eV at 0 K, but that of the S-type sample is 1.00 eV. A photoluminescence peak is observed at 0.97–0.98 eV for the D- and B-type samples, and often other emissions at ∼1.00 and 1.04 eV, while for the S-type sample, the peaks are observed at 0.93 and/or 0.95–0.96 eV. In conclusion, the activation energies of donors are ∼30 meV for In's in the Cu site and 5–10 meV for Se vacancies, and another level is expected to be ∼60 meV.