Epitaxial photoconductive detectors: a kind of photo-FET device

In epitaxial layers with a large area to thickness ratio, surface and interface space charge regions being, modulated by the incident light, behave as transverse Resistance-Capacitance systems modulating the effective volume that takes part in the layer electrical conductivity. Photoconductivity spectroscopy has been applied to gated and ungated GaAs samples, to validate present model. We also show that any sample conductivity variation due to the photoconductive effect (carrier concentration variation due to light absorption) is largely exceeded by the volume modulation effect due to the width variations of the space charge regions. Implications for optoelectronic characterization techniques are discussed.