Photoluminescence and photoconductivity in hydrogen-passivated ZnTe

Abstract

Hydrogen passivation effects in undoped p-ZnTe single crystals were studied by photoluminescence (PL) and photoconductivity (PC) measurements. Samples were exposed to r.f. hydrogen plasma at 250 c for different durations. Before passivation PL peaks were observed at 2.06 eV, 1.47 eV, 1.33 eV and 1.06 eV. After 60 min of exposure, samples showed strong band edge green luminescence at 2.37 eV due to an exciton bound to a Cu acceptor. In PC studies the dark current decreased by a factor of 70 on passivation for 60 min. From the temperature dependence of PC gain, the minority carrier lifetime τ_n was found to go through a maximum of 4.5 × 10^-7s at 220 K before passivation. After 60 min of hydrogenation, remained constant at 4.5 × 10^-7s for and T > 220 K decreased for T < 220 K. The activation energies of τ_n have been determined and show marked changes on passivation for T >220 K . Comparison between PL and PC studies showed that the deep acceptor level responsible for emission at 2.06 eV is passivated, giving rise to strong band edge emission at 2.37 eV, while emission due to the midgap impurity levels at 1.47, 1.33 and 1.05 eV remained unaffected. The thermal activation energies of PL peaks have also been determined and allow the construction of a defect energy level diagram for ZnTe.