Limitations of Field Plate Effect Due to the Silicon Substrate in AlGaN/GaN/AlGaN DHFETs

We investigated the limitations of the field plate (FP) effect on breakdown voltage V_BD that is due to the silicon substrate in AlGaN/GaN/AlGaN double heterostructures field-effect transistors. In our previous work, we showed that in devices with large gate-drain distance (L_GD > 8 μm), the breakdown voltage does not linearly increase with L_GD because of a double leakage path between the silicon substrate and the metal contacts, which makes the device break at the silicon interface. In this paper, we showed that the effect of the FP for such large L_GD is not significant because the breakdown is still dominated by the silicon substrate. The increase in V_BD due to the FP is significant only for devices with small gate-drain distances (L_GD <; 8 μm). Indeed we show that for such small L_GD the increase in the breakdown voltage is more than double, whereas for larger L_GD, this is only about 10%. Simulations of AlGaN/GaN/AlGaN devices for small L_GD are carried out with different FP lengths and passivation thickness in order to study the electric field distribution.