High Energy Distribution Function in an Electric Field and Electron Impact Ionization in AIIIBV Semiconductors

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A calculation method of the exponential dependence of the high‐energy distribution function in an electric field E is proposed for polar semiconductors. It is shown that in many‐valley semiconductors with complicated conduction band structure a strong anisotropy of the electron impact ionization coefficient α(E) will be obtained. In the case of E ∥ (100) or E ∥ (110) a ballistic transport in the Γ‐valley can occur and the dependence of In α vs.(E01/E) holds. If E ∥ (111) the ballistic transport in the Γ‐valley is impossible and the high‐energy distribution function is always formed due to electron scattering from X‐valleys. Then the dependence of In α vs.(E02/E)2 will be realized for a wide range of fields. The characteristic fields E01 and E02 are connected with the intervalley coupling constants for Γ—X and X—X scattering, respectively. Impact ionization processes are considered in detail for InSb, GaAs, and InP. The results are compared with accessible experimental data.