Photoluminescence and photoconductivity in hydrogen-passivated ZnTe

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 degrees C for different durati ons. 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 gre en 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 lifet ime tau(n) was found to go through a maximum of 4.5 x 10(-7) s at 220 K bef ore passivation. After 60 min of hydrogenation, tau(n) remained constant at 4.5 x 10(-7) s for T > 220 K and decreased for T < 220 K. The activation e nergies of tau(n) have been determined and show marked changes on passivati on for T > 220 K. Comparison between PL and PC studies showed that the deep acceptor revel O-Te responsible for emission at 2.06 eV is passivated, giv ing 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.