GaN-on-Si transistors attract increasing interest for power applications. However, the breakdown behavior of such devices remains below theoretical expectations, for which the Si substrate is typically made responsible. In this work, the effect of the thickness of an aluminum nitride buffer layer on the vertical breakdown voltage, measured relative to a grounded silicon substrate, has been investigated. A voltage-polarity-dependent breakdown mechanism has been observed. It has been found that the breakdown in the positive bias voltage regime is initiated by carrier injection, for which the carriers originate from an inversion channel formed between the epitaxial layers and the p-silicon substrate. TCAD simulations have confirmed the proposed explanations, and suggest that appropriate modification of the electronic structure at the AlN/silicon interface could significantly improve the vertical breakdown voltage.

We investigate the 3.32 eV defect-related emission band in GaN correlating transmission electron microscopy and spatially and spectrally resolved cathodoluminescence at low temperature. The band is unambiguously associated with basal plane stacking faults of type I 2 , which are a common defect type in semi-and nonpolar GaN grown on foreign substrates. We ascribe the luminescence to free-to-bound transitions. The suggested intrinsic acceptors involved have an ionization energy of ≈0.17 eV, and are located at the I 2 -type basal plane stacking faults.

We report about defect-related emission bands in GaN. We establish a direct correlation between results from spatially and spectrally resolved cathodoluminescence bands at 3. 32, 3.23, 3.20, 3.16, and 3.07 eV with findings obtained by transmission electron microscopy. The band around 3.32 eV was unambiguously assigned to I 2 basal plane stacking faults (BSFs). The bands at 3.23, 3.20, 3.16, and 3.07 eV were detected in sample regions, where BSFs exist, but were not assigned to specific defect types, except for the 3.07 eV line which is a phonon replica of the transition at 3.16 eV.

Back-gated measurements on conductive silicon substrates have been performed to investigate the effect of stress voltage on the dynamic behaviour of GaN-on-silicon (GaN-on-Si) transistors. Two comparable samples were studied with the only difference being the vertical dislocation density. Results show a clear correlation between dislocation density and the ability of the GaN buffer to dynamically discharge under high stress conditions.

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