On the interpretation of tunnelling into an amorphous semiconductor

Several recent measurements of the tunnel conductance G(V) in metal-insulator-amorphous semiconductor film junctions have shown, at V = 0, the G(0) ∝ exp (-BT^{- 1 4}) temperature dependence characteristic of the variable-range phonon-assisted tunnelling model of Mott. It is suggested, however, that observation of this temperature dependence for a bias V{right double angle bracket}kT e indicates failure to achieve tunnel injection and internal equilibrium in the amorphous film. At equilibrium in the low temperature case, effective electron-phonon coupling can lead to the proportionality G(V)∝ ∫ 0 eV ρ{variant}(E)dE where ρ{variant}(E) is the energy density of states, rather than to G(V) ∝ ρ{variant}(eV) as is commonly assumed.