Increased Mobility in 4H-SiC MOSFETs by Means of Hydrogen Annealing

Abstract

Enhancement-mode 4H-SiC MOSFETs utilising an aluminium oxide (Al2O3) dielectric without the requirement for an underlying silicon oxide (SiO2) layer have been shown to have a field effect mobility of 150 cm2V−1s−1 and a subthreshold swing of 160 mV/dec. The fabricated devices utilised a forming gas (3% H2 in N2) anneal immediately prior to the deposition of the Al2O3 by Atomic Layer Deposition (ALD). A comparison MOSFET using an identical Al2O3 deposition process with a 0.7 nm SiO2 layer had a field effect mobility of approximately 20 cm2V−1s−1. The hydrogen annealed device had a lower density of interface traps (Dit), a lower subthreshold swing, and a significantly reduced hysteresis in the transconductance data than the thin SiO2 sample. This finding solves the issue of inconsistency of device performance using thin film gate dielectric as an interfacial layer by offering a simple and controllable process.