<title>Investigation of the electronic properties of cadmium zinc telluride surfaces using pulsed laser microwave cavity perturbation</title>

Abstract

The spectroscopic performance of cadmium zinc telluride (CZT) room temperature radiation detectors is currently limited by both bulk and surface imperfections introduced during the growth, harvesting and fabrication of these devices. Bulk imperfections including impurities, vacancies, interstitials, grain boundaries and dislocations have been relatively well studied and are known to trap charge and reduce detector performance. However, the effect of specific traps on the electronic decay process has been difficult to quantify. Surface imperfections including mechanical damage or adsorbed chemical species are also known to trap charge or increase leakage current, but it has proven difficult to characterize the electronic properties of CZT surfaces prior to electrode deposition. Here it is shown that the pulsed laser microwave cavity perturbation method can provide important information on the electronic decay process both in the bulk and at the surface of high pressure Bridgman CZT crystals. Electronic decay process both in the bulk and at the surface of high pressure Bridgman CZT crystals. Electronic decay time was measured as a function of temperature and surface conditions. It is shown that the electronic decay process in bulk CZT is consistent witha single deep hole trap at an energy between 600meV and 700meV. The effect of surface quality was resolved by analyzing distinct features in the photoconductivity decay curves. Atomic force microscopy was used to characterize the surface roughness. Rough or damaged surfaces exhibited persistent photoconductivity, which could be eliminated by etching with a bromine methanol solution.