Cross-sectional Scanning Tunneling Microscopy on clean m-plane GaN and Ga vacancy identification

Gallium nitride has been studied thoroughly in the last decades as the material is relevant for applications in blue

light-emitting devices, UV laser diodes, high-power and high-frequency transistors. This material is however hardly

explored by cross-sectional Scanning Tunneling Microscopy (X-STM). We successfully investigated the clean m-plane

of the wurtzite GaN and studied the presence of Gallium vacancies by X-STM at liquid nitrogen temperature. We

observed the presence of Friedel oscillations around the defects and characterized the dependency of the oscillation

radius on the applied bias. This physical phenomenon combined with the tunnelling conditions leads us to understand

the charge state of the vacancy and the origin of the free carriers in GaN involved in screening the Ga-vacancies.

We observed a predicted bi-stability (by Hyun et al. 2016) of the N-atom neighbouring the Ga-vacancy and performed

Density Functional Theory (DFT) calculations to complement the experimental results. The result we achieved shows

that it is possible to obtain high-quality clean cleavages on GaN m-plane which allows for the study of other

nanostructured GaN-based materials and device structures.