To investigate the mechanism of the yellow luminescence in GaN, N-face GaN epitaxial film was prepared by wafer bonding and laser lift off from sapphire substrate. The exposed N-polar surface could be etched with potassium hydroxide aqueous solution. Intriguingly, it was observed that the yellow-to-band-edge luminescence ratio increased by 3.2 times after KOH etching. Since KOH etching was dislocation selective and changed the surface states of GaN, the outstanding increase of yellow luminescence was associated with the presence of surface states instead of dislocations. It was further confirmed by X-ray photoelectron spectroscopy studies that the Ga vacancies dominated the yellow luminescence in GaN.

Gallium Vacancies Related Yellow Luminescence in N-Face GaN Epitaxial Film. H.Xu, X.Hu, X.Xu, Y.Shen, S.Qu, C.Wang, S.Li: Applied Surface Science, 2012, 258[17], 6451-4