Semiconductor Detectors Diodes and Diode Array Systems

3 Semiconductor Detectors Diodes and Diode Array Systems 

Solid semiconducting materials are extremely important in eleetronies and instrumentation, including their use as radiation detectors. To understand the behavior of a semieonduetor, it is necessary to briefly describe the bonding in these materials. 

Silicon has the valence electronic structure 3s 3p. The partially filled p orbitals might lead one to suppose that silicon has a partially filled valence band and would therefore be an electrical conductor. Because silicon is covalently bonded, the two 3s electrons and the two 3p electrons occupy sp hybrid orbitals. This results in a solid with two electron energy bands, each with four closely spaced sublevels, one for each electron in the valence shell of Si. The four electrons occupy and fill the valence band at 0 K and are therefore nonconducting. However, at temperatures above 0 K, a few electrons can be thermally promoted from the valence band into the conduction band there, they become conductors of electricity. When an electron leaves the valence band, it leaves behind a positive hole that is also mobile, thus producing an electron-hole pair. Both the electron and the hole are charge carriers in a semiconductor. Semiconductors such as Si and Ge are called intrinsic semiconductors their behavior is a result of the bandgap and band structure of the pure material. 

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Semiconductor Detectors—Diodes and Diode Array Systems... 

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