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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 the 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 detrapping time constants. [ABSTRACT FROM AUTHOR]

This work describes electrical characteristics and the correlation to material properties of high electron mobility transistor structures with a C-doped GaN current blocking layer, grown either by an extrinsic or auto-doping process with different doping levels. Increasing degradation of crystalline quality in terms of threading dislocation density for increasing C-doping levels was observed for all samples. Different growth conditions used for the auto-doped samples played no role for overall degradation, but a higher fraction of threading screw dislocations was observed. Independent of the doping process, 90% of all TSDs were noted to act as strong leakage current paths through the AlGaN barrier. This was found statistically and was directly verified by conductive atomic force microscopy in direct correlation with defect selective etching. Vertical breakdown was observed to increase with increasing C-concentration and saturated for C-concentrations above around 1019 cm−3. This was attributed to an increasing compensation of free charge carriers until self-compensation takes place. A progressive influence of TDs for high C-concentrations might also play a role but could not be explicitly revealed for our material. [ABSTRACT FROM AUTHOR]