Analysis of Dimension Dependence in Quasi-Vertical GaN Schottky Barrier Diodes

Quasi-vertical (QV) GaN Schottky barrier diodes (SBDs) have emerged as a promising device architecture that overcomes the limitations of conventional lateral and vertical SBDs while offering high electrical performance. However, the influence of the lateral and vertical current-transport dimensions on the electrical characteristics of QV GaN SBDs has not been systematically evaluated. In this study, the effects of the anode-to-drift length (LAD), drift-to-cathode length (LDC), and drift-layer thickness (DLT) on the DC and RF characteristics were systematically investigated. Variations in LAD and LDC produced relatively modest changes in the forward conduction characteristics, with the current density decreasing by up to 15% and the specific on-resistance (RON,SP) increasing by up to 29%, while the breakdown voltage (BV) varied by less than 4%. Increasing the DLT from 0.5 to 4 μm produced substantially larger variations, reducing the current density by 62% from 11.38 to 4.28 kA/cm2 and increasing RON,SP by 171% from 0.17 to 0.46 mΩ·cm2, while BV increased from 55 to 199 V. The stronger dependence on DLT, particularly in reverse blocking capability, identifies DLT as the dominant geometrical parameter governing the DC characteristics. RF characterization as a function of DLT showed that the series resistance (Rs) strongly depended on DLT, whereas the junction capacitance (Cj) exhibited comparatively moderate variation. The DLT = 0.5 μm device exhibited the highest estimated RC cutoff frequency (fc) of 18.2 GHz, whereas the DLT = 1 μm device maintained a relatively high fc of 15.3 GHz while providing a more balanced DC and RF performance. The device with LAD/LDC = 7/5 μm and DLT = 1 μm exhibited RON,SP = 0.21 mΩ·cm2, turn-on voltage (VON) = 0.54 V, and BV = 128 V. These findings provide practical guidelines for the dimensional design of QV GaN SBDs for microwave rectifier applications.