Analysis of Cr-Doped CdGeAs2 Using Thermal Admittance Spectroscopy

Abstract

AbstractThe optical and electrical properties of chrome-doped CdGeAs2 (CGA), an important non-linear optical material, are reported. CGA, a chalcopyrite semiconductor of the pseudo- III-V type, is a close ternary analog to GaAs, possessing significant differences. To date, the electrical and optical properties of as-grown undoped CGA have been controlled by a somewhat shallow dominant residual acceptor which it is the source of significant undesirable optical absorption. Highly transparent semi-insulating CGA should be attainable using compensation and counterdoping schemes similar to those used for GaAs. However, identifying suitable deep and shallow n-type and p-type dopants will require extensive empirical studies. As a starting point of survey to find deep levels, the properties of CGA:Cr have been investigated. Cr is a reasonable choice as it has been used extensively to provide a deep level in GaAs. Thermal Admittance Spectroscopy was used to examine the electrically active levels in this material. These measurements were correlated with temperature dependent Hall effect measurements, and IR absorption measurements. SIMS analysis was utilized to estimate the Cr concentration as the segregation coefficient for Cr in CGA has not been reported.. The results show that there is a p-type level introduced into the band gap at about 0.16 eV above the valence band, a value nominally 50% deeper than that of the native acceptor. The background doping as measured by Capacitance-Voltage measurements was determined to be 8 × 1016 cm−3 near the surface, and 1.0 × 1017 cm−3 in the bulk. These results are compared to similar measurements in undoped material.