Reduction of current collapse in NH3-MBE-grown <i>in situ</i> SiN/AlGaN/AlN/GaN high electron mobility transistors on a SiC substrate

The aim of the present work is to investigate in detail the effect of SiN coating on the electrophysical properties of high electron mobility transistors and to compare the obtained results of the conventional AlGaN barrier coating with the GaN-cap layer. Both of them were fabricated on identical AlGaN/GaN heterostructures. In this work, pulse measurements of current–voltage characteristics from different quiescent points revealed a 4.5-fold reduction in the gate-lag effect on the sample with the SiN-cap, compared to the GaN-cap coated sample. A simple technique for analyzing the behavior of the channel resistance as a function of the gate voltage is proposed to determine the threshold voltage stability and to measure the resistance of the channel regions apart from the under-gate region. When the AlGaN/GaN HEMT surface is passivated by a SiN-cap layer, the threshold voltage instability is practically not detectible for gate-lag measurements, in contrast to surfaces with a GaN-cap coating. It is shown that the nature of the traps involved in the gate-lag effect is different from the nature of the traps involved in the drain-lag phenomenon.