A photoluminescence study of vanadium-related defects in n-type, semi-insulating and p-type Cd(Zn)Te

Abstract

A photoluminescence (PL) study of vanadium-related defects in semi-insulating and co-doped p-type and n-type CdTe:V crystals gives evidence of the presence of the V 2+–Zn complex. In addition to the 3 T 2( F)→ 3 A 2( F) emission of V 3+ near 0.5 eV and the 4 T 2( F)→ 4 T 1( F) transition of V 2+ near 0.45 eV, two further luminescence bands are detected at higher energies. The first emission band (I), peaking around 0.8 eV, is correlated to the V 2+–Zn complex and the second one (II), peaking around 0.6 eV, is attributed to the acceptor level introduced by the cadmium vacancies. Varying the zinc concentration in CdTe, we analyse the behaviour of the vanadium impurity charge state. We show that the V 2+ internal transition decreases with zinc alloying due to the formation of the V 2+–Zn complex. The emission bands related to isolated V Cd are present with high intensity only in the p-type crystals, in which all the vanadium content is in the V 3+ oxidation state, whereas, in the semi-insulating and n-type crystals, the PL spectrum is dominated by Emission I related to the V 2+–Zn complex. The presence of this complex in the semi-insulating crystals used in photorefractive (PR) applications and the dominance of this complex over the optical properties of Cd(Zn)Te:V imply the contribution of this complex to the PR processes.