Impact of Substrate Resistivity on the Vertical Leakage, Breakdown, and Trapping in GaN-on-Si E-Mode HEMTs

This paper presents an extensive investigation of the impact of the resistivity of the silicon substrate on the vertical leakage and charge trapping in 200 V GaN-on-Si enhancement-mode high-electron mobility transistors. Three wafers having different substrate resistivities were submitted to combined DC characterization, step-stress experiments, and electroluminescence (EL) analysis. The results described within this paper demonstrate that: 1) the use of a highly resistive silicon substrate can increase the vertical breakdown voltage of the transistors, due to the fact that the voltage drop on the GaN buffer is mitigated by the partial depletion of the substrate (this latter causes a plateau region in the drain to substrate I-V characteristic) and 2) highly resistive substrate results in stronger trapping effects, due to the capacitance of the depleted substrate and the resulting backgating effects. The results described within this paper indicate that the choice of the resistivity of the substrate is the result of a tradeoff between high breakdown voltage (that could be in principle achieved through a highly resistive substrate) and the minimization of trapping processes (which can be hardly obtained with a resistive substrate).