Physics and Engineering of Radiation Detection

7.2. Position Sensitive Detection 447

Anodes

Cathodes

Substrate

(a)

Drift Plane

Anodes Cathodes

Drift Plane

Substrate

Enclosure

(b)

Figure 7.2.6: (a) Top and (b) cross-sectional view of a typical MSGC.

The drift plane is kept at a distance of a few millimeters from the sub-

strate.

case is a semiconductor material. The commonly used materials to build SMSDs
are silicon and germanium, with silicon being the most popular. Silicon microstrip
detectors are now seen as standard tracking devices used in high energy physics ex-
periments. On the other hand, germanium based detectors have also been built and
employed for versatile applications such as x-ray spectroscopy and medical imaging.
The biggest problem with microstrip semiconductor detectors is that their dimen-
sions are limited by the dimensions of the semiconductor wafer, which can not be
made larger than a few tens of a centimeter. Therefore to built a large area detector
one must use several small size detectors placed close together.
Two variants of the basic structure of a simple one-sided silicon microstrip de-
tector are shown in Fig.7.2.7. Here the base material or substrate is an n-type
semiconductor, which has been implanted with strips of n+ material. A reverse bias
is established between these strips and the aluminum implantation on the other side
of the silicon wafer. This creates a depletion region, which for best performance