| Summary: | In this paper, we fabricated Gallium Nitride (GaN) vertical <i>p</i>-<i>i</i>-<i>n</i> diodes grown on free-standing GaN (FS-GaN) substrates. This homogeneous epitaxy led to thicker GaN epi-layers grown on the FS-GaN substrate, but a high crystalline quality was maintained. The vertical GaN <i>p</i>-<i>i</i>-<i>n</i> diode showed a low specific on-resistance of 0.85 mΩ-cm<sup>2</sup> and high breakdown voltage (BV) of 2.98 kV. The high breakdown voltage can be attributed to the thick GaN epi-layer and corresponds to the mesa structure. Improvement of the device characteristics by the mesa structure was investigated using device simulations. We proved that a deeper mesa depth is able to decrease the electric field at the bottom of the mesa structure. Furthermore, a smaller mesa bevel angle will assist the BV up to 2.98 kV at a 60° bevel angle. Our approach demonstrates structural optimization of GaN vertical <i>p</i>-<i>i</i>-<i>n</i> diodes is useful to improve the device performance.
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