Characterization of Defect Levels in Doped and Undoped CuGaSe2 by Means of Photoluminescence Measurements

Abstract

Photoluminescence properties of various as-grown, annealed, and doped CuGaSe2 samples have been investigated in the range from liquid helium temperature to room temperature in order to determine extrinsic and intrinsic defect levels of this material. The observed spectra of undoped samples can be described using two acceptor and three donor levels. We propose VCu (55 meV) and Sei (95 meV) as acceptor and VSe (80 and 110 meV) and Gai (110 to 120 meV) as donor levels, respectively. The spectra of intentionally doped CuGaSe2 single crystals were dominated by broad donor–acceptor pair transitions. The formation of extrinsic donor levels is in accordance with the results of electrical measurements, which indicated a strong compensation of the p-type materials. Sn-, Ge-, Si-, and B-doped crystals exhibited one broad emission band below 1.45 eV, whereas samples doped by group II atoms showed two radiative transitions. The activation energies for CdCu, MgCu, ZnCu, and IIGa were estimated to 80, 90, 110, and 210 meV, respectively.