Metal-induced gap states modeling of metal-Ge contacts with and without a silicon nitride ultrathin interfacial layer

Metal-induced gap states (MIGS) modeling is used to elucidate the lack of Fermi level pinning at metal-insulator−Ge interfaces. Energy band diagram assessment reveals the existence of two dipoles at the metal-insulator and the insulator−semiconductor interface. The metal−insulator dipole modulates the metal-insulator interface electron barrier and the voltage drop across the insulator but does not affect the barrier to electron transport across the metal-insulator−Ge interface. Rather, this electron transport barrier is established by the metal-semiconductor work function difference and the insulator−semiconductor dipole. Thus, the lack of Fermi level pinning at a metal-insulator−Ge interface is attributed to the fact that the electron transport barrier does not depend upon MIGS screening. A quantitative formulation of this metal-insulator−semiconductor interface MIGS-based model confirms the lack of Fermi level pinning. Furthermore, it indicates that care must be taken when assessing experimental barrier height- work function data since the slope parameter should only be evaluated for the range of metal work function in which the semiconductor is in depletion. This range of work function for which the semiconductor is in depletion is quite limited for the case of a narrow bandgap semiconductor, such as Ge.