Development of Large-Area CdTe/n+-Si Epitaxial Layer-Based Heterojunction Diode-Type Gamma-Ray Detector Arrays

Growth of large area single crystal CdTe layers was studied on 25 × 25 mm
²
(211) Si substrates using metalorganic vapor phase epitaxy. High crystalline quality thick crystals with very good material uniformity were obtained. A 2-D monolithic detector array comprising (20 × 20) pixels was developed and evaluated. Each pixel is 1.12 × 1.12 mm
²
size in a 1.17-mm pitch and consists of a p-CdTe/n-CdTe/n
⁺
-Si heterojunction diode structure, which is isolated from the surrounding pixels by making deep vertical cuts. The detector array exhibited highly uniform and low dark current, typically less than 0.5-μA/cm
²
per pixel at an applied reverse bias of 50 V. The spectroscopic performance was separately confirmed by dicing out a small portion from the array which clearly resolved energy peaks from
²⁴¹
Am gamma isotopes at room temperature. On the other hand, a significant improvement in the detection property was observed by cooling it to -30 °C.