Optically enhanced photoconductivity in semi-insulating gallium arsenide

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Abstract
Time evolution of photoconductivity of semi-insulated gallium arsenide illuminated at low temperatures with monochromatic 0.7–1.8 eV photons was studied. For low light intensity the photosensitivity increases with time by several orders of magnitude and exhibits different dynamics for above-the-gap and below-the-gap energy photons. For various photosensitivity stages the concentration of charge trapped in deep traps was determined by measuring thermally stimulated current. Six deep traps in the 85–250 K temperature range were observed. Good correlation between the photosensitivity and the total concentration of trapped charge was found. The increase of photosensitivity is interpreted as the increase of lifetime of optically created free holes due to the trapping of electrons, which therefore are not available for recombination. The same interpretation also gives a new insight in previously published results on increased photosensitivity in gallium arsenide.