Development of high-resolution CdTe radiation detectors in a new M-π-n design

The authors have developed M-pi-n (metal high-resistivity p-type crystal, highly n-type epilayer) CdTe detectors in a new design that are suitable for X-ray and gamma-ray spectrometry in the range of a few tens to several hundred kilo-electron volts. Using high-resistivity single crystal CdTe substrates (resistivity similar to 10(9)Omega.cm), an iodine-doped n-CdTe layer was grown homoepitaxially on one face of each wafer at a low substrate temperature of 150 degrees C using the hydrogen plasma radical assisted metalorganic chemical vapor deposition technique. An indium electrode was deposited on the n-CdTe side as an ohmic contact by evaporation without heating the crystals, while a gold electrode was deposited on the opposite side for metallic contact. Leakage current was decreased to around 0.5 nA for a 2 x 2 mm(2) detector of thickness 1 mm at room-temperature (18 degrees C) and around 10 pA at -15 degrees C for an applied negative bias of 350 V. Low leakage currents in the detector enabled the authors to apply higher bias voltages resulting in better charge collection efficiency and improved spectral responses for different radioisotopes.