Solid State Electronic Devices, 7th Edition

4.1 Optical Absorption¹

An important technique for measuring the band gap energy of a semiconductor is the absorption of incident photons by the material. In this experiment photons of selected wavelengths are directed at the sample, and relative transmission of the various photons is observed. Since photons with energies greater than the band gap energy are absorbed while photons with energies less than the band gap are transmitted, this experiment gives an accurate measure of the band gap energy.

It is apparent that a photon with energy hv ≥ E_g can be absorbed in a semiconductor (Fig. 4–1). Since the valence band contains many electrons and the conduction band has many empty states into which the electrons may be excited, the probability of ...