Photo-assisted Kelvin Probe Force Microscopy Investigation of Three-dimensional GaN Structures

Despite the relatively advanced progress in the development of 3D GaN-based devices, there is a weak understanding of illumination-induced surface charge transfer processes (fast and slow processes occurring on different time scales). An insight understanding of the surface charge transfer process may lead to significant improvements in the performance of 3D GaN devices especially in sensor applications (as its performance is affected by its response and the recovery times). To date, most of the studies have been concentrated on the c-oriented GaN surface. Therefore this work investigates the behavior of fast and slow charge transfer processes of varying doping types and crystal orientation of 3D GaN structures, using surface photo-voltage measurements performed by photo-assisted Kelvin probe force microscopy:The effect of various wavelengths of illumination on the SPV processes of n-type and p-type c-plane GaN micro-structure is presented in this work for the first time. The obtained results provide new additional information on the predominant processes of the studied phenomena separating contributions of the fast from slow surface states. The important role of silane injection during growth and surface treatment by phosphoric acid on the SPV behavior semi-polar facet of 3D GaN columns was demonstrated for the first time. According to the surface treatment, it can be considered an effective way to enhance the response of GaN nanostructure-based sensor devices. Moreover, our findings expand our knowledge of the illumination-induced charge transfer processes at the 3D GaN surface and add to some information that might be relevant in assessing the high performance of this material for applications in optoelectronic gas sensors.