How Indium Nitride Senses Water

Abstract

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.

The Itinerant 2D Electron Gas of the Indium Oxide (111) Surface: Implications for Carbon‐ and Energy‐Conversion Applications

“…By assuming an exponential surface potential well model and an out‐of‐plane effective electron mass of m z ≈ 0.11 m e , we extract a surface potential of ≈1.29 eV, declining within ≈34 Å (i.e., ≈3 unit cells, u.c.) into the bulk . The quantum well potential V ( z ) (black line), the bound state energies (gray lines) as well as the bound wave function solutions (red lines) are shown in Figure f.…”

“…However, the spectral intensity exhibits a periodic modulation (Figure S1, Supporting Information), resulting from the interference of photoelectrons emitted from individual crystal layers in the near surface region. This reflects the out‐of‐plane periodicity (along [111]) of the recurring In 2 O 3 layers (as seen in the schematics of the experimental geometry relative to the In 2 O 3 unit cell in Figure b) and is consistent with findings in other 2DEG systems (e.g., InN, TiO 2 , SrTiO 3 ) . Fourier transforming the wave function solutions found from the extracted quantum well potential in Figure c, we can accurately predict this photoemission intensity (Figure h), which independently validates our characterization approach.…”

Electrical Characterization of InN Nanowire/Si Heterojunctions

“…The simulation also fits the trends with and without water absorption. With water, a higher surface band bending is reported (Figure a) leading to a larger distribution of the barrier heights within one single InN NW/Si heterojunction. As a consequence, the barriers at the surfaces play a larger role for the electrical behavior in case of water adsorption, whereas for the annealed sample the barriers, expected for bulk InN, dominate.…”

“…a) Fermi level pinning above the conduction band edge at the NW surface . A larger downward band bending is reported with water adsorption at the InN surface . Nextnano++ simulations of InN/Si junctions with b) p‐type Si and c) n‐type Si (dashed).…”

Two-dimensional Electron Gas at Thiol/ZnO Interface

“…Another possible explanation for the intensity enhancement is that, on the surfaces of n-type semiconductors such as ZnO [13,16], CdxZn1−xO [19], InN [20], etc., the metallic state is intensified when the center of the bulk Brillouin zone (the Γ point), where the bottom of the conduction band is located, is probed. In the present case of the ethanethiol/ZnO(0001 _ ) surface, the excitation light at hν = 88 eV can probe the state at k z = 50 nm −1 in the normal emission geometry, which is closer to the Γ point (k z = 48.3 nm −1 ) than k z = 44 nm −1 by hν = 65 eV, as shown in Figure 1(c).…”