Noise properties of pixelated polycrystalline CdTe detector

Abstract

Polycrystalline CdTe film is promising detector material for large-area, direct type X-ray image sensor. But polycrystalline materials usually have instability, non-uniformity, and large dark currents. These properties are deeply related with the as grown detector material quality. The noise property of a sensing material is a figure of merit in itself, and gives additional information about the detector material properties. In this paper, a 20 μm-thick CdTe polycrystalline film is prepared by thermal evaporation. Arrays of metal patterns having pitch from 100 to 500 micrometres were deposited on the CdTe film to make a pixelated detector. Dark current and noise spectrum of the polycrystalline pixels were measured. The fabricated polycrystalline CdTe pixel has ohmic characteristics with a resistivity of ∼ 6.6 × 108 Ω cm. An excess low frequency noise, which is considered to be originated from metal-CdTe contact rather than polycrystalline material itself, was measured.