Different reverse leakage current transport mechanisms of planar Schottky barrier diodes(SBDs) on sapphire and GaN substrate

The effects of different substrates on the off-state leakage current in gallium nitride (GaN) planar diodes are experimentally demonstrated and studied by analyzing temperature-dependent current–voltage characteristics. The two devices exhibit different leakage mechanisms despite being subjected to the same process conditions. The device with a sapphire substrate shows a more intricate leakage mechanism, implying the presence of additional leakage channels compared to the device with free-standing substrates. The electrical leakage characteristics in the planar GaN-on-sapphire device (referred to as utemp-SBD) and GaN substrate device (referred to as usub-SBD) Schottky barrier diodes (SBD) can be described by two distinct processes as the reverse bias gradually increases: utemp-SBD go through the thermionic emission (TE), variable range hopping (VRH), Frenkel–Poole (FP) emission and space-charge-limited conduction (SCLC) model; The leakage conduction mechanism of usub-SBD include TE, VRH, and FP emission mechanisms. It is noteworthy that in device 1, there is a rapid increase in leakage current within the voltage range of −36 to −40 V, primarily driven by the SCLC mechanism. This effect arises due to the presence of intrinsic traps in GaN grown on a heterogeneous substrate. Additionally, in the voltage range of −7 to −50 V (348 K to 448 K), the leakage mechanism shifts from FP emission to the VRH model, possibly due to variations in the Schottky barrier height.This study provides an in-depth analysis of the leakage mechanisms observed on different substrates and offers valuable insights for the design of planar gate transistors to minimize or avoid the occurrence of leakage channels.