GALLIUM-RELATED DEFECT CENTERS IN MOLECULAR-BEAM-EPITAXY-GROWN ZNSE FILMS - INFLUENCE OF ELECTRIC-FIELD ON THERMAL EMISSION OF ELECTRONS

We report a study of the Poole-Frenkel (PF) effect in ZnSe. Our result s show that ignoring the PF effect in deep-level transient spectroscop y (DLTS) leads to a significant scatter in the activation-energy data reported in the literature for deep defects in this material. The Ga-d oped ZnSe films used in this study were grown on (100) GaAs by molecul ar-beam epitaxy. Our DLTS results show the presence of two prominent e lectron traps at depths E1 = 0. 27 and E2 = 0.40-0.48 eV. The E2 trap exhibits a strong PF effect, indicating a donorlike character. Thermal emission from the E1 trap is independent of the electric field. By ta king into account the PF effect, we are able to explain the carrier-co ncentration dependence of the activation energy of trap E2. The captur e process for the E1 trap is thermally activated with a thermal-energy barrier of 0.096 eV. The existence of a thermal barrier for the carri er capture leads to persistent photoconductivity observed below T = 90 K. In order to describe the properties of the Ga-related traps in ZnS e:Ga films, we propose a consistent defect model involving complexes o f Ga atoms with zinc vacancies in the next-nearest-neighbor positions (Ga(Zn)-V(Zn)). The model attributes the E2 level to a donorlike state , and the E1 level to an acceptorlike state of Ga(Zn)-V(Zn) defect com plex.