Chapter 3 - BAND STRUCTURE

Abstract

This chapter discusses the band structure of group III–V element. Many of the electrical and optical properties of a pure semiconductor can be explained in terms of a band structure, which is the energy E(k) of an electron expressed as a function of its wave number vector k. The major features of the band structure are known for some of the III–V compounds, but the detailed structure has not been established to the same degree as in germanium and silicon. The III–V compounds have band structures of the same type as the group IV semiconductors, though there are some differences that arise from the lack of inversion symmetry in the compounds. These compounds all appear to have a similar valence band structure. The band, as in germanium and silicon, is degenerate at the center of the zone, there being a heavy-hole band and a light-hole band, and also a third band split off by the spin–orbit interaction. The maxima of the valence band do not, however, lie exactly at the zone center, but some small distance away. The conduction band structure varies considerably from compound to compound. All compounds have minima of the conduction band lying on the [100] and [111] directions and at the zone center, but in compounds of high mean atomic number, the lowest minimum is that at the center of the zone, whereas in compounds of lower atomic number, the lowest minima are those on the [100] or [111] directions.