Charge transport mechanism in CdTe-based p-n junction detectors formed by laser irradiation

Charge transport mechanism responsible for leakage current in X/gamma-ray detectors with a p-n junction formed in semi-insulating p-like CdTe single crystals by laser-induced doping is studied. The In/CdTe/Au diodes showed high rectification and good spectral response to high-energy radiation, however samples were suffering from an increase in leakage current and deterioration of the characteristics with time. The proposed energy diagram allows to explain the reverse I-V characteristic of the diodes. At low voltages, the Sah-Noyce-Shockley theory describes well both the shape of the I-V characteristic and its temperature changes. At higher voltages, measured currents deviate from the theoretically calculated values toward increasing. An additional current increase is attributed to injection of electrons from the "near-ohmic" Au/CdTe contact and their diffusion to the p-n junction. When the current increases, the drift component is also included in injection of electrons. This leads to a rapid rise in the current contribution with increasing bias voltage and limits possibility to extend the detector active region by increasing the applied voltage.