Deconvolution of the Mg-Related blue band in GaN via selective chemical treatments

The deep electronic states associated with the Mg-related blue band in GaN are traditionally attributed to bulk defects. Using surface photovoltage spectroscopy to monitor selective wet etching ([Formula: see text], [Formula: see text], [Formula: see text]), complemented by X-ray photoelectron spectroscopy and secondary ion mass spectrometry, we investigate their surface-mediated origin. Depth profiling confirms that the as-grown surface features a segregated magnesium-oxygen phase confined to the near-surface region, while 2D chemical mapping reveals its lateral distribution becomes highly inhomogeneous and defect-localized after [Formula: see text] etching. Surface photovoltage data indicate that the blue-band transition comprises two components: a minor planar state ([Formula: see text]) and a dominant defect-anchored state ([Formula: see text]). [Formula: see text] treatment quenches the planar component but only partially suppresses the defect signal, reflecting etchant inaccessibility within threading dislocation cores. Conversely, [Formula: see text] and [Formula: see text] treatments induce signal polarity inversion via hole trap formation; [Formula: see text] eliminates the defect signature likely due to fluorine passivation. Crucially, bulk magnesium concentrations remain completely unperturbed by etching. These findings provide direct physical evidence that these states arise from surface and interface environments rather than bulk complexes, highlighting the profound impact of surface electronic configurations on GaN device properties.