Theory of surface‐defect states and Schottky barrier heights: Application to InAs

Theoretical predictions of electronic energy levels associated with s‐ and p‐bonded substitutional point defects at (110) surfaces of InAs and other III–V semiconductors are presented and discussed. The specific defects considered for InAs are: anion and cation vacancies, the (native) antisite defects In_As and As_In, and 26 impurities. The predicted surface‐defect deep levels are used to interpret Schottky barrier height data for (a) n‐ and p‐(InAs) and (b) the alloys Al_xGa_1−xAs, GaAs_1−xP_x, In_1−xGa_xP, and In_1−xGa_xAs. The rather complicated dependence of the Schottky barrier height φ_B on alloy composition x provides a nontrivial test of the theory (and competing theories). The following unified microscopic picture emerges from these and previous calculations: (1) For most III–V and group IV semiconductors, Fermi‐level pinning by native defects can explain the observed Schottky barrier heights. (2) For GaAs, InP, and other III–V semiconductors interfaced with nonreactive metals, the Fermi‐level pinning is normally due to antisite defects. (3) When InP is interfaced with a reactive metal, surface P vacancies are created which pin the Fermi level. (4) Impurities and defect complexes are sometimes implicated. (5) At Si/transition‐metal‐silicide interfaces, Si dangling bonds pin the Fermi level. (6) These defects at the semiconductor/metal interfaces are often ‘‘sheltered’’ or ‘‘encapsulated.’’ That is, the states responsible for Fermi‐level pinning are frequently ‘‘dangling‐bond’’ states that dangle into a neighboring vacancy, void, or disordered region. The defects are partially surrounded by atoms that are out of resonance with the semiconductor host, causing the defect levels to be deep‐level pinned and to have energies that are almost independent of the metal.