Insights into ultraviolet-induced electrical degradation of thermally grown SiO2/4H-SiC(0001) interface

The harmful impact of ultraviolet (UV) light irradiation on thermally grown SiO2/4H-SiC structures was investigated by means of electrical measurements of metal-oxide-semiconductor (MOS) capacitors. Unlike Si-based MOS devices, significant electrical degradation, such as positive flatband voltage (VFB) shift and hysteresis in the capacitance-voltage (C-V) curves of SiC-MOS capacitors was induced by UV irradiation with a low-pressure mercury lamp. The interfacial fixed charge density increased with UV-irradiation (22.6 mW/cm2 for 16 h) to 1.7 × 1012 cm−2, which was an order of magnitude larger than that of the as-grown SiO2/SiC interface. A detailed study based on single wavelength solid-state UV lasers revealed that there was a threshold photon energy at around 5 eV and a moderate dependence of UV-induced degradation on temperature. These experimental findings imply that pre-existing inactive defects accumulated at the thermally grown SiO2/SiC interface were transformed to active carrier traps with high-energy UV irradiation through transparent SiO2 layers.