Current Collapse in Buffer-Free GaN-on-SiC Power Transistors: Maxwell-Wagner Effect and Related Model

Recently, the use of insulating substrates has emerged as a viable option for the fabrication of GaN power transistors exceeding 1 kV. Such structures are of interest because no doped buffer is used, so-ideally—a low dynamic RDSON is expected. This article investigates the recoverable (and temperature dependent) current lowering induced by negative backgating in buffer-free GaN-on-SiC devices. Remarkably, we demonstrate that such an effect is not directly related to charge trapping, but to the Maxwell-Wagner effect, i.e., the charge migration at the interface between the insulating SiC substrate and the semi-insulating GaN layer. Accordingly, a model is defined and validated to simulate with great accuracy, the current decreases (and related kinetics) as a function of temperature, voltage, and time.