Vertical breakdown of GaN on Si due to V-pits

Gallium Nitride on silicon (GaN/Si) is an important technological approach for power electronic devices exhibiting superior performance compared to devices based on a pure silicon technology. However, the material defect density in GaN/Si is high and identification of critical defects limiting device reliability is still only partially accomplished because of experimental difficulties. In this work, Atomic Force Microscopy, Scanning Electron Microscopy, Secondary Ion Mass Spectrometry, and Cathodoluminescence were employed to investigate commonly occurring epitaxial overgrown V-pits and inhomogeneous incorporation of oxygen and carbon across layer stacking in vertical direction. These experiments identified V-pits as regions with higher n-type carrier concentrations and paths for vertical leakage through the buffer, as directly probed by Conductive Atomic Force Microscopy. The deleterious effect of V-pits on device performance is demonstrated by evaluating test devices fabricated on two wafers with significantly diverse density of buried V-pits induced by varying growth conditions of the Aluminum Nitride nucleation layer. A clear correlation between observed vertical breakdown and density of V-pits within the C-doped GaN-layer below the device structures is obtained. Back-gating transient measurements also show that the dynamic device behavior is affected by the V-pit density in terms of the de-trapping time constants.