Comparison of Sb, As, and P doping in Cd-rich CdTe single crystals: Doping properties, persistent photoconductivity, and long-term stability

Abstract

Acceptor doping CdTe with group-V elements is promising for increasing the power conversion efficiency of CdTe photovoltaic devices via an increased hole concentration and open circuit voltage (VOC). In past work, we have investigated doping with As in Cd-rich CdTe single crystals grown using the Cd-solvent traveling heater method we have developed. In this study, we compare the doping parameters and stability of hole concentration in the light and dark for P, As, and Sb dopants in crystals cooled very slowly from the growth temperature to approximate thermal equilibrium. In contrast to older reports of a high acceptor ionization energy for Sb, our temperature dependent Hall effect experiments reveal an acceptor ionization energy slightly above 90 meV for Sb doping in the mid 1016 cm−3 range. Room temperature hole concentrations above 1016 cm−3 are observed for P, As, and Sb with each dopant type exhibiting only small changes in hole concentrations over 2 years' time at room temperature. Crystals doped with P, As, or Sb exhibit increased conductivity after above-gap illumination, which decays over periods of minutes to hours depending on temperature. Analysis of the photoconductivity decay reveals a barrier attributed to hole capture of 190–280 meV for the series P, As, and Sb.