Effects of (NH4)2Sx treatment on indium nitride surfaces

Abstract

Indium nitride (InN) surfaces treated with ammonium sulfide [(NH4)2Sx] are investigated using Hall effect measurement, x-ray photoelectron spectroscopy (XPS), and scanning Kelvin probe microscopy (SKPM). Upon the (NH4)2Sx treatment, the sheet carrier density is reduced by (0.8–0.9)×1013 cm−2, leading to an increase in the sheet resistance. By numerically solving the Poisson’s equation, the associated upward shift of the surface band bending is derived to be 0.3 eV. XPS characterization shows, on the (NH4)2Sx treated InN surface, the formation of native oxide is effectively suppressed and a covalently bonded sulfur layer with surface In atoms is formed. This surface In–S dipole layer results in an increase in the electron affinity, thus giving rise to a lower surface bending shift (0.2 eV) observed in XPS. The electron affinity increase of 0.1 eV can be deduced, which is consistent with the result obtained by SKPM. Thus, the (NH4)2Sx treatment has been demonstrated to be an effective method for reducing the surface band bending for InN.