Fabrication of CdTe detectors in a new p-i-n design for gamma-ray spectroscopy

CdTe and related compound semiconductors are useful for high energy flux detection at room temperature. We propose a new fabrication technique for CdTe detectors in p-i-n design that is suitable for hard x-ray and gamma-ray spectroscopy. Using a high resistivity single crystal CdTe substrate, an iodine doped n-CdTe layer is grown homoepitaxially on one face of the crystal using the hydrogen plasma-radicals- assisted metalorganic chemical vapor deposition method working at a low substrate temperature of 150 degrees C. An indium electrode is evaporated on the n-CdTe side for an ohmic contact, while a gold electrode is placed on the opposite side which acts as a p-type contact. The p-i-n detector thus fabricated exhibited low leakage current at room temperature operation, below 0.5 nA at an applied bias of 350 V for a 2 X 2 mm2 detector of thickness of 1 mm. Leakage current further decreased to 16 pA at 350 V while cooling the detector down to -15 degrees C. Spectral responses of the detector showed improved energy resolution for different radioisotopes of energies in the range form few tens of keV to several hundred keV and stable operation when operated at high applied biases or slightly cooling the detector. Performance of the different detectors thus fabricated will be presented.