Practical Surface Treatments and Surface Chemistry of n-Type and p-Type GaN

X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) were used to study the electronic structure of n-GaN and p-GaN(0001) surfaces after three ex situ surface treatments: aq-HCl, annealing in NH3, and annealing in HCl vapor. The combination of in situ vacuum annealing and re-exposure of samples to air revealed that the adsorption of ambient contaminants can reduce the surface state density and subsequent band bending on both n-GaN and p-GaN surfaces. Insights derived from first-principles calculations of the adsorption of relevant species on the Ga-terminated GaN(0001) surface are used to explain these experimental observations qualitatively.