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

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 V²⁺–Zn complex. In addition to the ³T₂(F)→³A₂(F) emission of V³⁺ near 0.5 eV and the ⁴T₂(F)→⁴T₁(F) transition of V²⁺ 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 V²⁺–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 V²⁺ internal transition decreases with zinc alloying due to the formation of the V²⁺–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 V³⁺ oxidation state, whereas, in the semi-insulating and n-type crystals, the PL spectrum is dominated by Emission I related to the V²⁺–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.