Enhanced Surface Potential Variation on Nanoprotrusions of GaN Microbelt As a Probe for Humidity Sensing

Surface potential (SP) using Kelvin probe microscopy is employed, as a measure to sense humidity, exploiting localized nanoprotrusions of freestanding GaN microbelts. These belts with distinct nanofeatures are grown using chemical vapor deposition technique in the vapor−solid process. The variation of SP value is associated with the surface charge accumulation. Pronounced enhancement of the SP variation is found to arise from the localized inhomogeneity on the nanoprotrusions of microbelt. Role of oxygen-related native defect complexes is also discussed for the observed SP variation with humidity. Furthermore, the rough surface of belts favors a high level of defects on the surface and appears more sensitive to moisture level in atmosphere. Hence attention is essential for any sensing application of chemical species using GaN. A dissociative path way for the reaction mechanism of water molecules on GaN surfaces has been predicted.