Space-and-time current spectroscopy of GaAs-based detectors

We report space-and-time current spectroscopy for characterization of high-quality GaAs thin films grown on semi-insulating gallium arsenide substrates. The approach is based on illumination of semiconductor material with an oscillating interference pattern formed of two light waves, one of which is phase modulated with frequency ω. The non-steady-state photocurrent flowing through the short-circuited semiconductor is the measurable quantity in this technique. The alternating current is resulted from the periodic relative shifts of the photoconductivity and space charge electric field gratings, which arise in the crystalʹs volume under illumination. The experiments are carried out in the geometry of Michelson interferometer at the illumination wavelength of 532 nm. The dependence of the non-steady-state photocurrent on spatial frequency of the interference pattern is measured allowing estimation of the diffusion length of photoelectrons in GaAs thin film LD=40 μm.