Vertically aligned GaN nanotubes - Fabrication and current image analysis

In this work, we present a one step formation method of nanotubes on GaN film, and then map out local current of nanotubes. GaN nanotubes were formed by inductively coupled plasma (ICP) etching and found that tops of these nanotubes were hexagonal with the c-axis perpendicular to GaN substrate surface. With a certain concentration of Argon gas, we found that the radius of the whole nanotubes used in this study was around 40 nm, the radius of the nanocavities inside these nanotubes was around 20 nm while the density of the nanotubes was around 4.4 × 10⁹ cm^-2. Conductive atomic force microscopy (C-AFM) was then used to investigate the local conductivity in both of the as-grown GaN film sample and vertically aligned nanotubes sample. Focusing on the nanotubes etched planes, we investigated the top end of the nanotubes and the outer edge of the nanotubes. We found that the surrounding areas of these nanotubes aligned with respect to the c-plane etching direction showed a significantly higher conductivity than that on the top of the nanotubes. As a result, current measured from the nanotubes sample was more than two orders of magnitude larger than that measured from the as-grown film sample.