Electron affinity and surface states of GaN <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>m</mml:mi></mml:math>-plane facets: Implication for electronic self-passivation

Abstract

The electron affinity and surface states are of utmost importance for designing the potential landscape within (heterojunction) nanowires and hence for tuning conductivity and carrier lifetimes. Therefore, we determined for stoichiometric nonpolar $\mathrm{GaN}(10\overline{1}0)$ $m$-plane facets, i.e., the dominating sidewalls of GaN nanowires, the electron affinity to $4.06\ifmmode\pm\else\textpm\fi{}0.07\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ and the energy of the empty Ga-derived surface state in the band gap to $0.99\ifmmode\pm\else\textpm\fi{}0.08\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ below the conduction band minimum using scanning tunneling spectroscopy. These values imply that the potential landscape within GaN nanowires is defined by a surface state-induced Fermi-level pinning, creating an upward band bending at the sidewall facets, which provides an electronic passivation.