Structural and electrical properties of polycrystalline CdTe films for direct X-ray imaging detectors

We introduce polycrystalline cadmium telluride (CdTe) with high atomic number and density, low effective energy and wide band gap for application in large area diagnostic X-ray digital imaging. In this work, polycrystalline CdTe films were fabricated on ITO/glass substrate by both physical vapor deposition (PVD) with slow deposition rate and pressure of 10−6 Torr and the closed space sublimation (CSS) method with high deposition rate and low vacuum pressure(10−2 Torr). The various polycrystalline CdTe films were grown at different deposition rates and substrate temperatures. Physical properties such as microstructures and the crystal structure of the polycrystalline samples were investigated by SEM and XRD patterns respectively. The PVD method resulted in microstructures with columnar shape and more uniform surface, while the CSS method produced microstructures with many larger grains and less uniform surface. The films were polycrystalline structures with a preferential (111) direction. The electrical and optical properties such as the dark current as a function of applied bias voltage and X-ray sensitivity of the fabricated films were measured and investigated under X-ray exposure.