CHEMICAL TRENDS OF BARRIER HEIGHTS IN METAL-SEMICONDUCTOR CONTACTS - ON THE THEORY OF THE SLOPE PARAMETER

The barrier heights in ideal metal-semiconductor contacts are determin ed by the continuum of the metal-induced gap states (MIGS). In general izing Pauling's concept, the charge transfer across such interfaces ma y be modeled by the difference X(m) - X(s) of the metal and the semico nductor electronegativities. For n-type semiconductors this MIGS-and-e lectronegativity model describes the chemical trends of the barrier he ights as phi(Bn)= phi(cn1) + S-x(X(m) - X(s)). The zero-charge transfe r barrier heights phi(cn1) were calculated for almost all semiconducto rs. The slope parameters S-x are determined by the density of states o f the MIG states, the thickness of the respective interfacial double l ayer, and the interface dielectric constant epsilon(i). The densities of states and decay lengths of the metal-induced gap states at their c harge neutrality level were computed by others for some of the semicon ductors. It is demonstrated that these theoretical data predict the sl ope parameters S-x to vary proportional to (epsilon(infinity) - 1)(2)/ epsilon(i) where epsilon(infinity) is the electronic contribution to t he static dielectric constant of the semiconductor. This result confir ms a previously found semi-empirical rule.