Correlation of reverse dark current-voltage characteristics and gamma detection properties of a p-CdTe/n-CdTe/n+-Si vertical diode-type radiation detector

The reverse dark current mechanism of a p-CdTe/n-CdTe/n⁺-Si vertical diode-type gamma ray detector, fabricated by growing epitaxial CdTe on Si substrates was studied and corelated with the detector's gamma detection properties. The detector dark current deviated from the Shockley-Reed-Hall (SRH) generation mechanism but showed tunneling was the dominant process. The dark current was strongly controlled by the dislocation densities and their distribution in the CdTe epilayer. Detectors that exhibited poor gamma detection properties had high dislocation densities and had large and nearly temperature independent dark currents. Good working detectors, on the other hand, showed small dark currents with a clear temperature dependence. These working detectors, fabricated with optimized crystal growth techniques, had a dislocation density nearly an order of magnitude lower than those of non-working or poorly working detectors.