Noise and Efficiency of Semiconductor Devices

Abstract

We now treat the two basic semiconductor photodetectors—the photoconductor and the photodiode. In the latter case, we also discuss the avalanche photodiode, which is the semiconductor analog of the photomultiplier. The photoconductor is a device composed of a single uniform semiconductor material; the incident optical power is measured by monitoring the conductance. The change of conductance is produced by creation of free carriers in the material by the presence of the radiation. In contrast, the photodiode is a p-n junction, in which photoinduced carriers in the vicinity of the junction modify the current-voltage characteristic so that the radiation level may be measured. In the case of the reverse-biased semiconductor photodiode, the behavior is almost identical to that of the vacuum photodiode.