Origin of electron accumulation at wurtzite InN surfaces

Abstract

The origin of electron accumulation at wurtzite InN surfaces is explained in terms of the bulk band structure. Ab initio calculations of the electronic structure of wurtzite InN reveal an unusually low conduction band minimum at the $\ensuremath{\Gamma}$-point. As a result, the branch point energy, ${\mathrm{E}}_{B},$ which is the crossover point from donor-type to acceptor-type surface states, is located in the conduction band at the $\ensuremath{\Gamma}$-point. This allows donor-type surface states to exist in the conduction band. The donor-type surface states emit their electrons into the conduction band, thus giving rise to electron accumulation at the surface. Experimental measurements, probing the conduction band electron plasma, confirm the existence of electron accumulation at InN surfaces, with a surface Fermi level location in agreement with the predictions of the ab initio theory.