Influence of growth conditions and polarity on interface-related electron density in InN

Electron accumulation at the oxidized surface of In- and N-polarity indium nitride is shown to exhibit no dependence on the growth conditions (varied from In- to N-rich), revealing the surface Fermi level to be pinned 1.4 +/- 0.1 eV above the valence band maximum for all cases. This is in contrast to the interpretation of recent multiple-field Hall effect measurements, which suggested almost an order of magnitude increase in the sheet density of the accumulation layer upon moving from In-rich to N-rich growth conditions, and sample thickness dependent single-field Hall effect measurements which suggested different surface sheet densities for In- and N-polarity samples. However, an increase in the electron density approaching the InN/GaN (buffer layer) interface was not considered in the analysis of these Hall effect measurements, and this is invoked here to reconcile the constant surface Fermi level with the variations in excess sheet density observed in the previous Hall effect studies.