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Comparison of reverse current mechanisms in GaN Schottky diodes grown on sapphire versus ammonothermal GaN substrates

In this work, we analyse the reverse current mechanisms in GaN Schottky barrier diodes (SBDs) grown on sapphire and native GaN substrates. For the sapphire-substrate sample, two conduction mechanisms are identified: Poole-Frenkel emission (PFE) and trap-assisted tunneling (TAT), with corresponding trap energy levels of 0.9 eV and 0.3 eV, respectively. In contrast, only PFE is observed in the GaN-substrate sample, with a trap energy of 0.75 eV, suggesting that the presence of TAT is related to the higher dislocation density in structures grown on sapphire substrates. The leakage mechanisms and associated trap energies are extracted by comparing experimental current-voltage (I-V) characteristics with a model that includes thermionic emission and tunneling contributions for different temperatures, from 298K up to 443K.