p-Type Surface Defects on n-GaN Nanorods.

Nanowire surfaces are of particular interest, primarily for their potential in optoelectronic applications. Thus, different surface treatments have been performed to develop methods for controlling the surface effect. Here, we successfully shifted the n-type surface states in n-type GaN nanorods to p-type states in the challenging regime, i.e., the blue regime. This was achieved through reverse charge transfer driven by an electrostatic field induced by surface strain. The p-type surface state demonstrates an inverted photovoltage mechanism, as well as a stable blue photoluminescence at room temperature under ambient conditions, within the n-type GaN nanorods. The inverted charge transfer at the surface of the GaN nanorod array was determined by X-ray photoelectron spectroscopy (XPS), surface photovoltage, Kelvin probe, Raman, and photoluminescence measurements. The mechanism and the study's conclusions have been supported experimentally and theoretically. This surface state inversion approach offers a new strategy for regulating p-n junctions in low-dimensional nanomaterials.