Vertical GaN Schottky barrier diodes: Impact of device dimensions and micro-masking on mesa edge termination

The effect of edge termination on vertical GaN Schottky barrier diode (SBD) performance by the formation of mesa etch structures is investigated. While forward bias electrical characteristics (on-resistance, threshold voltage, ideality) were not affected by mesa edge termination, breakdown voltage (VBD) showed an ∼87% improvement compared to planar SBD structures without edge termination (VBD ∼ 230 V), increasing proportionally with mesa etch depth and inversely with the separation between the anode contact and the mesa edge up to VBD ∼ 430 V. Device simulation showed similar trends, suggesting the mechanism of breakdown voltage enhancement is the suppression of peak electric fields within the GaN region beneath the anode contact edges. While device simulations suggest that devices with deep (2 μm) mesa edge termination and low mesa–anode separation (0.3 μm) should have featured VBD of ∼600 V, the experimentally observed lower breakdown, voltage in this regime was attributed to the effects of defects at the mesa-terminated edge associated with micro-masking that occurred during etching of the deep mesa structures, which was due to re-deposition of the Ni hard mask.