Metal-induced gap states

The case of non-vanishing A is shown in Fig. 4.22(b). From this figure we observe that A = m + T homo - 7e- Here we have assumed a common energy level, Ep, for both metal and semiconductor. This is not quite exact since the metal induces electronic states in the semiconductor gap that in turn may induce CT and... 

This mcclianism is not so efrcctivc in polar semiconductors. The conversion of empty hybrids to doubly occupied hybrids on a GaAs surface would require the double occupation of a gallium hybrid, which is unfavorable because of the polar energy. Indeed, recent experiments (Chye, Babalola, Sukegawa, and Spicer, 1975) indicate that the I crmi level is not pinned on surfaces of GaP at the vacuum. Nonetheless, Schottky barriers can arise at GaP- metal interfaces. Metal-induced surface states" have been proposed as a mechanism (discussed in Section 18-1 ) but the barriers could well arise simply from incorporation of metal atoms in the semiconductor or vice versa. 

For the cases of Na and Ca on DP7, the spectra shown are for the saturated systems Ca- DP7 and Na2" DP7 . For AI/DP7, the spectrum shown is for a few monolayers (equivalent) coverage, since the Al atoms remain essentially on the surface. All spectra are well reproduced by the DOVS derived from the results of the LSD calculations. The metal atom-induced gap states (for Ca and Na) are well resolved in both the experimental and theoretical spectra. In particular, the splitting between the soliton and antisoliton states in Na DP7- is 0.75 eV in the experimental spectrum and 0.8 eV in the theoretical spectrum. For Ca DP7-, on the other hand, because of the electrostatic interaction of... 

Similarly, in a metal/semiconductor junction, in which the metal work function lies between the valence band maximum and the conduction band minimum, the tails of the metallic wave function decrease exponentially in the adjacent semiconductor gap states, inducing transfer of charge, which in turn creates the dipole. The mismatch between the metal Fermi level and E is reduced by this dipole (by a factor inversely proportional to the semiconductor s optical dielectric constant, s o, in first approximation [51]). Only in the case of semiconductors with a large optical dielectric constant or high density of interface states is the Fermi level almost completely pinned at E- In this case, since E is an intrinsic property of the semiconductor, the Schottky barrier height of a particular semiconductor is independent of the metal (and its work function) utilized as contact. In order to define the CNL, one... 

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