The operation of the intrinsic IR photodetector is based on band-to-band transitions caused by absorption of the photons in a narrow-gap semiconductor. Among the many types of IR photodetectors, intrinsic photodetectors offer the best performance at high temperatures.
The wide body of information now available concerning different methods of crystal growth and physical properties of materials used for IR photodetectors makes it difficult to review all aspects in detail. As a result, only selected topics are reviewed in this chapter. More information can be found in many comprehensive reviews and monographs (see, for example, Refs. 1â8).
The properties of narrow-gap semiconductors that are used as the material systems for IR detectors result from the direct energy bandgap structure: a high density of states in the valence and conduction bands, which results in strong absorption of IR radiation and a relatively low rate of thermal generation. Table 3.1 compares important parameters of narrow-gap semiconductors used in IR detector fabrication.
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