Scanning electron microscopy imaging of multilayer-doped GaN: Effects of surface band bending, surface roughness, and contamination layers on doping contrast

Dopant profiling by a scanning electron microscope possesses great potential in the semiconductor industry due to its rapid, contactless, non-destructive, low cost, high spatial resolution, and high accuracy characteristics. Here, the influence of plasma and wet chemical treatments on doping contrast was investigated for a multilayered p-n GaN specimen, which is one of the most promising third-generation wide bandgap semiconductors. Angle-resolved x-ray photoelectron spectroscopy and atomic force microscope were employed to characterize the degree of surface band bending, surface roughness, gallium oxides, and hydrocarbons on the surface of GaN. N2 and air plasmas were unable to remove the surface contamination layers, although the degree of surface band bending was suppressed. In contrast, wet chemical methods offer superior capability in removing contamination layers; however, the surface roughness was increased to varying degrees. Notably, NH4F solution is capable of improving the doping contrast. The underlying mechanism was elucidated from the perspective of surface band bending, surface roughness, and contamination. The findings reported here will provide a feasible solution for effective characterization of semiconductor materials and devices.