Passivation and reconstruction-dependent electron accumulation at sulphur treated InAs(0 0 1) surfaces

The effects of in situ sulphur passivation on the electronic properties of n-type InAs(0 0 1) have been studied using X-ray photoemission spectroscopy and high resolution electron energy loss spectroscopy coupled with space-charge layer calculations. Surfaces passivated by sulphur dosing followed by arsenic capping were annealed in vacuum to progressively remove the protective layers. For disordered surfaces with a sulphur coverage of almost 2 monolayers (ML), complex surface plasmon modes were observed due to strong electron accumulation at the surface, with downward band bending around 600 meV. For (2×1) reconstructed surfaces (sulphur coverage <1 ML), the band bending dropped to 325 meV. A 375 °C anneal was sufficient to remove all sulphur and regain a clean (4×1) indium-terminated surface with 200 meV downward band bending. We discuss the reconstruction-dependent surface accumulation and some aspects of ‘electrical passivation’ of surfaces.