The unique electronic
band structure of indium nitride InN, part
of the industrially significant III–N class of semiconductors,
offers charge transport properties with great application potential
due to its robust n-type conductivity. Here, we explore
the water sensing mechanism of InN thin films. Using angle-resolved
photoemission spectroscopy, core level spectroscopy, and theory, we
derive the charge carrier density and electrical potential of a two-dimensional
electron gas, 2DEG, at the InN surface and monitor its electronic
properties upon in situ modulation of adsorbed water.
An electric dipole layer formed by water molecules raises the surface
potential and accumulates charge in the 2DEG, enhancing surface conductivity.
Our intuitive model provides a novel route toward understanding the
water sensing mechanism in InN and, more generally, for understanding
sensing material systems beyond InN.