Effect of the metal nature on the I-V characteristics of CdTe diodes for ionizing radiation detectors

Abstract

The electrical characteristics of CdTe-based surface barrier structures, which can be used as spectroscopic X/γ-ray detectors, have been investigated. The metal-semiconductor structures were obtained by thermal (resistive) vacuum deposition of various metals onto detector-grade CdTe crystals. Metals with different work functions, such as Al, In, Ni, Ti, Cr, and Au, were employed as electrode materials for rectifying contacts. An ohmic contact was created on the entire opposite surface of the crystals by chemical deposition of Au from a gold chloride solution. The surface processing of CdTe crystals before the formation of both rectifying and ohmic contacts included mechanical and chemical polishing, as well as Ar-ion bombardment. Dark currents at reverse voltage of 1500 V did not exceed 4 nA for all the diodes except for the Au/CdTe/Au structure. The effect of the metal nature on the I-V characteristics and charge carrier transport mechanisms was studied, and the features of voltage dependences of dark current were explained by differences in the work functions of the metals, as well as the contact deposition technique.