Vertical and lateral GaN rectifiers on free-standing GaN substrates

Edge-terminated Schottky rectifiers fabricated on quasibulk GaN substrates showed a strong dependence of reverse breakdown voltage $V_B$ on contact dimension and on rectifier geometry (lateral versus vertical). For small diameter (75 μm) Schottky contacts, $V_B$ measured in the vertical geometry was ∼700 V, with an on-state resistance ${\mathrm{(R}}_{\mathrm{ON}})$ of 3 mΩ cm², producing a figure-of-merit $V_B^2{\mathrm{/R}}_{\mathrm{ON}}$ of 162.8 MW cm⁻². Measured in the lateral geometry, these same rectifiers had $V_B$ of ∼250 V, $R_{\mathrm{ON}}$ of 1.7 mΩ cm² and figure-of-merit 36.5 MW cm⁻². The forward turn-on voltage ${\mathrm{(V}}_F)$ was ∼1.8 V (defined at a current density of 100 A cm⁻²), producing $V_B{\mathrm{/V}}_F$ ratios of 139–389. In very large diameter (∼5 mm) rectifiers, $V_B$ dropped to ∼6 V, but forward currents up to 500 mA were obtained in dc measurements.