Engineering Physics

8.2 Intrinsic semiconductors—carrier concentration

Pure germanium or silicon crystal is called an intrinsic semiconductor. Each semiconductor atom possesses four valence electrons in the outermost orbit. To get stability, each of these atoms has to get eight electrons in the outermost orbit, so that each atom makes four covalent bonds with the surrounding four other atoms in the crystal. A two-dimensional representation of the crystal structure of silicon (or germanium) at 0 K is shown in Fig. 8.1(a). The band diagram of this material is shown in Fig. 8.1(b).

At 0 K, all the valence electrons of Si atoms are participating in covalent bonds and their energies constitute a band of energies called valence band. So, at 0 K, valence band is completely ...