Dynamical properties of electron and hole generated in CdTe radiation detector probed by optical pulses

Characteristics of CdTe radiation detectors are studied using laser pulses. To improve the spatial and time resolution of carrier generated position and time, optical laser pulses were used for carrier generation and the electrical response from the CdTe radiation detectors were detected as a function of irradiated position and time. The detector measured in this study was Schottky contact CdTe detectors with a thickness of 0.5 mm and a size of 2 × 1 mm
²
. Laser light from laser diode with a wavelength of 850 nm were modulated to pulses by using pulse generator and were irradiated to the side surface of the CdTe detectors. The pulse width and the period were 2 ns and 2 ms, respectively. The incident light power was 30 nW, which correspond to one photon energy of γ or X lay with a energy of around 70 keV. Time traces of output voltage amplified by pre-amplifier were measured by oscilloscope. Pulse height and rise-up time of the output voltage depended on the distance from the anode plane of the detector. These dependences were changed by changing applied bias voltage. It is concerned that the depletion layer are increased with increasing the bias voltage and the distribution of the output voltage value in the detector are changed. This probing technique should be suitable for measuring the carrier distribution and transportations in the CdTe radiation detectors.