The surface electronic properties are key parameters for the design of nitride based transistor or sensor devices. For Indium Nitride (InN), a promising material for electronic and optoelectronic applications, device realization is very challenging particularly due to a commonly formed strong electron accumulation layer at the InN surface and its interfaces to other materials. Understanding the intrinsic surface properties that lead to the formation of the accumulation layer might open new approaches to avoid or modify and control the surface electron concentration.
In this talk I will present investigations of the surface electronic and chemical properties, measured by in-situ photoelectron spectroscopy (UPS, XPS), of polar and nonpolar oriented InN thin films prepared by plasma-assisted molecular beam epitaxy. Thereby I will show, that the surface band alignment and the formation of the electron accumulation layer are correlated with the energetic position of occupied electron states, which are different for different InN surface configurations. Furthermore, I will present experiments that reveal that the surface properties are significantly modified by adsorbates as characterised by surface exposure to oxygen, water, hydrogen and ammonia.