X-ray response of polycrystalline - CdZnTe

X-ray response of polycrystalline-CdZnTe deposited by thermal evaporation were measured by signal to noise(S/N) analysis. The CdZnTe material has optimal property adquem in solid state X-ray detector and many research presented on single crystal CdZnTe with small sized silicon readout device, but it would be difficult to apply CdTe or CdZnTe single crystal to large area-flat panel detectors such as radiography and mammography. Alternatives of single crystal, we have grown high resistivity polycrystalline CdZnTe (>5times10⁹ Ohm cm) thick films by thermal evaporation method on carbon substrate. A high signal-to-noise has a direct impact on the performance of CdZnTe X-ray detectors. Important image parameter such as dynamic range and detective quantum efficiency, rely on the signal and noise characteristics of the system. In this paper, the S/N of high resistivity polycrystalline CdZnTe detector different detector thickness with different pixel size and applied bias voltage has been measured. The detector design is planar, 35 mmtimes15 mm with different pixel electrode size and different detector thickness (up to 150 mum). The electrical signal was amplified by a Burr-Brown ACF2101 low-noise current to voltage conversion amplifier. The increase of the S/N with bias voltage and detector thickness is due to the enhanced charge collection efficiency and energy absorption efficiency, respectively. At bias voltage 5 V, the 150 mum thick CdZnTe detector with 100 mum pixel size operate in the saturation region, at 65 kV_p with a tube current of 7.5 mA and an exposure time of 0.6 sec