The p-n Junction Operating as a Detector

The operation of a semiconductor detector is based, essentially, on the properties of the p-n junction with reverse bias (Fig. 7.18). Radiation incident upon the junction produces electron-hole pairs as it passes through it. For example, if a 

5-MeV alpha particle impinges upon the detector and deposits all its energy there, it will create about 

Electrons and holes are swept away under the influence of the electric field and, with proper electronics, the charge collected produces a pulse that can be recorded. 

The performance of a semiconductor detector depends on the region of the p-n junction where the electric field exists (region of width Xq, Fig. 7.18). Electrons and holes produced in that region find themselves in an environment similar to what electrons and ions see in a plate ionization chamber (see Sec. 

There are some differences, however, between these two types of detectors. 

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