Laser-induced pulse shapes in partially depleted epitaxial GaAs radiation detectors

Measurements of laser-induced pulse shapes are reported in partially-depleted 150 μm thick epitaxial GaAs, carried out as a function of device temperature and bias voltage. Residual impurity concentrations of 1–4×1014 cm−3 at room temperature drop to 7×1013 cm−3 at 219 K, resulting in a significant increase in the depth of the space charge region. A focussed pulsed laser beam was used to probe the cleaved edge of a device and so investigate the dependence of the signal pulse shape on the interaction distance from the Schottky contact. Carrier lifetimes of up to 500 μs were observed consistent with charge diffusion in the low-field region of the device. Photo-induced current transient spectroscopy measurements provide further evidence of a number of mid bandgap traps with peak emission rates between 300–330 K.