Feasibility study of direct-conversion x-ray detection using cadmium zinc telluride films

Abstract

Polycrystalline Cd(Zn)Te films deposited by vacuum thermal evaporation are investigated as a direct-conversion medium for x-ray detection. The use of evaporation techniques allows for the preparation of large-area films with the potential for large-area x-ray imaging with high spatial resolution. Films with compositions of Cd1-xZnxTe (x = 0.15,0.25,0.3) were prepared to a thickness of 20 μm on slide glass substrates with an aluminum or indium tin oxide (ITO) bottom electrode and a silver top electrode, with and without additional charge-blocking layers (CeO2 and parylene dielectric) between the electrode and CdZnTe film to reduce leakage current. Composition and structural analyses of the as-deposited films confirm the development of polycrystalline CdZnTe. Leakage current in the CdZnTe film is approximately ten times lower than for a comparable CdTe film, and the lowest leakage is obtained for a film with composition of Cd0.7Zn 0.3Te The use of ITO rather than aluminum as the bottom electrode provides a further improvement in leakage current and improved stability. The Cd0.7Zn0.3Te-based device with ITO electrode and charge-blocking layers achieves the highest total output charge (180.44 pC/cm2 or 1.1 × 109 e-/cm2) and signal-to-noise ratio (6.19 at applied bias of 30 V). The present experiments show that Cd1-xZnxTe in a multilayer structure with charge-blocking layers is feasible as a good radiation conversion layer for flatpanel radiation imaging systems. © 2012 IOP Publishing Ltd and SISSA.