Physics and Engineering of Radiation Detection

5.1. Semiconductor Detectors 299

of electron hole pairs in the undepleted region is a major problem. It not only

produces non-linearity in detector’s response but can also decrease the response

time due to diffusion of charges across the regions.

As we saw the increasing the bias voltage is not always possible to solve these
problems. A convenient solution to increase the depletion width is to introduce
an intrinsic layer of a semiconductor material between the p and n materials (see
Fig.5.1.31). This so called PIN (P-type, Intrinsic type, N-type) structure is perhaps
the most commonly used configuration of semiconductor detectors. The main ad-
vantage of introducing an intrinsic material in the middle is that it essentially fixes
the depletion width to the width of the intrinsic region. In this way a large depletion
width becomes available without the need for very high reverse bias. This solves
most of the problems associated with simple pn junctions.

− +

Depletion Region

p i n

(a)

V

(b)

p i nn+

Radiation

(c)

Ohmic Contacts

Figure 5.1.31: A simplified structure (a)

of a reverse biased PIN diode and its ide-

alized electric field profile (b). A realistic

PIN structure is shown in (c).

K.2 SchottkyDiode.........................

Up until now we have only discussed the utilization of a junction, produced by p
and n types of semiconductors, as a radiation detector. A similar junction can also
be produced by bringing a semiconductor and a metal in contact with each other.
Such a semiconductor-metal junction can also be exploited for radiation detection
purposes.