Shear-Induced Changes of Electronic Properties in Gallium Nitride.

We show that sliding on the surface of GaN can permanently change the surface band structure, resulting in an increased degree of band bending by more than 0.5 eV. We hypothesize that shear and contact stresses introduce vacancies that cause a spatially variant band bending. Band bending is observed by shifts and broadening of core-level binding energies toward lower values in X-ray photoelectron spectroscopy. The extent of band bending is controlled by humidity, number of sliding cycles and applied load, presenting opportunities for scalable tuning of the degree of band bending on a GaN surface. Scanning transmission electron microscopy revealed that the epitaxy of GaN was preserved up to the surface with regions of defects near the surface. The hypothesized mechanism of band bending is shear-induced defect generation, which has been shown to affect the surface states. The ability to introduce band bending at the GaN surface is promising for applications in photovoltaics, photocatalysis, gas sensing, and photoelectrochemical processes.