Relationship between high resistivity and the deep level defects in CZT∶ In

摘要

The high resistivity performance for an indium doped Cd_(0.9)Zn_(0.1)Te crystal (CZT∶In), grown by the modified vertical Bridgman (MVB) method and under Te-rich conditions, was investigated by the relationship between the deep donor level E_(DD) and the Fermi level. Using the temperature-dependent resistivity measurement, the energy value of Fermi level was evaluated to be 0.740 eV, which almost approaches the mid-gap of CZT∶In. Further, the carrier transport behaviors were characterized by gamma-ray energy spectroscopy response with various bias voltages. The determination of the carrier mobility-lifetime products and the broadening in the photo-peak resolution implied incomplete charge collection which can be attributed to the deep level defects in the band gap. Therefore, the deep level defects were identified by thermally stimulated current (TSC) spectroscopy in the temperature range of 25-310 K. Fitted by the plots of the natural logarithm of current intensity ln(I_(DC)) versus 1/(kT), the E_(DD) level dominated by dark current was characterized to be 0.704 eV near the mid-gap. As a deep donor level of doubly ionized Te antisite (Te_(cd)~(2+)) existed in the CZT∶In crystal grown under excess tellurium conditions, the origin of E_(DD) level was ascribed to Te_(cd)~(2+) below the conduction band. As a result, the E_(DD) level can stabilize the Fermi level deep near the mid-gap of CZT∶In and the resulting high resistivity.