Classical Photon Detectors: Simple Photoconductor and Photovoltaics

This chapter describes the detection mechanism, characteristics, and operation common to all photon detectors. Photon detectors work because of bandgaps in the detector material. The chapter illustrates this with details for two classic photon detectors: a simple photoconductive (PC) detector, and a simple photodiode (photovoltaic, or PV) detector. It discusses very general descriptions of simple PC and PV structures, and describes the photocurrent, responsivity, and noise for these devices. If a material can be made into both PC and PV devices, then PV devices are preferred because they have a better theoretical signal‐to‐noise value, simpler biasing, and more reliable prediction of responsivity and noise. The chapter derives equations to predict the photocurrent and responsivity. The block of electronics to which one connects the detector allows to set the detector bias and converts photocurrents to voltages. This block of electronics referred to as the front‐end, or first‐stage, or bias‐control circuit.