Page 87 - Photonics Essentials an introduction with experiments

Photoconductivity

Photoconductivity 81

Figure 5.4. The applied electric field separates the electron–hole pair. The electron is
moving 12 times faster than the hole.

this case, the electron velocity is about 12 times greater than the
hole velocity.
In Fig. 5.4, the electric field created by the applied voltage sepa-
rates the electron–hole pair spatially. The electron, which has a high-
er mobility moves toward the positive contact faster than the hole
moves toward the negative contact.
The electron will reach the positive contact first and exit the semi-
conductor, as shown in Fig. 5.5. This creates a net positive charge in
the semiconductor, which is compensated by the introduction of an
electron by the negatively biased ohmic contact.

Figure 5.5. The electron reaches the positive contact and is detected in the external cir-
cuit. In order to maintain charge neutrality in GaAs, the negative ohmic contact intro-
duces an additional electron.

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.