Theory of Photoelectric Emission from Semiconductors

The yield vs energy relation is determined for a number of possible photoelectric production and escape mechanisms involving volume and surface states in semiconductors. Calculations are based on density-of-states considerations and involve energy-band expansions to lowest nonvanishing order about the threshold point. The "direct" and "indirect" processes involving volume states have yields proportional to $E-E_T$ and ${(E-E_T)}^{\frac{5}{2}}$, respectively. Both processes appear to have been identified experimentally by Gobeli and Allen. The linear yield also requires, in addition to production by "direct" optical excitation, that the observed photoelectrons escape without scattering in the volume or at the surface. Energy and angle distribution functions of the emitted carriers are also determined.