Behavior of deep defects after hydrogen passivation in ZnTe studied by photoluminescence and photoconductivity

摘要

The effects of hydrogen passivation 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 deg for different durations. Before passivation PL peaks were observed at 2.06eV, 1.47 eV, 1.33 eV and 1.06 eV. After 60 minutes exposure, samples showed strong band edge green luminescence at 2.37 eV due to an exciton bound to a Cu acceptor. Further exposure to lasma resulted in disappearance of 2.37eV and 2.34 eV peaks due to damage. In PC studies the dark current was found to decrease by a factor of 70 on 60 minutes passivation. From the temperature dependence of PC gain, the minority carrier lifetime #tau#_n was found to go through a maximum of 4.5x10~(-7) sec at 220 K before passivation. After 60 minutes exposure, #tau#_n remained constant at 4.5x10~(-7) sec for T>220 K and decreased for T<220 K. The activation energies of #tau#_n were determined and show marked changes on passivation for T>220 K. Comparison between PL and PC studies showed that the deep acceptor level O_(Te) 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 the PL peaks have also been determined and allow the construction of a defect energy level diagram for ZnTe.