On the response behavior of fast photoconductive optical planar and coaxial semiconductor detectors

Fast optical detectors use photoconductive effects in semiconducting channels or thin films. The behavior of those planar and coaxial detectors is reviewed. It is shown that p-type and n-type materials show different behavior in respect to bandwidth and gain. The strong influence of the contacts is clarified and the surface recombination is taken into account. The bandwidth of those detectors is evaluated and the gain and gain bandwidth product are given in terms of the geometry and material data. Furthermore, the influence of deep levels and of a depletion layer along the surface is considered, which considerably affect the static characteristics as well as the pulse response. Regarding these effects, the different behavior of GaAs- and Ga
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As-conductive photodetectors is demonstrated.