Temperature and SiO2/4H-SiC interface trap effects on the electrical characteristics of low breakdown voltage MOSFETs

The temperature and carrier-trapping effects on the electrical characteristics of a 4H silicon carbide (4H-SiC) metal-oxide-semiconductor field effect transistor (MOSFET) dimensioned for a low breakdown voltage (BVDS) are investigated. Firstly, the impact of the temperature is evaluated referring to a fresh device (defects-free). In particular, the threshold voltage (Vth), channel mobility (µch), and on-state resistance (RON) are calculated in the temperature range of 300 K to 500 K starting from the device current-voltage characteristics. A defective MOSFET is then considered. A combined model of defect energy levels inside the 4H-SiC bandgap (deep and tail centers) and oxide-fixed traps is taken into account referring to literature data. The simulation results show that the SiO2/4H-SiC interface traps act to increase RON, reduce µch, and increase the sensitivity of Vth with temperature. In more detail, the deep level traps in the mid-gap have a limited effect in determining RON once the tail traps contributions have been introduced. Also, for gate biases greater than about 2Vth (i.e., VGS >12V) the increase of mobile carriers in the inversion layer leads to an increased screening of traps which enhances the MOSFET output current limiting the RON increase in particular at low temperatures. Finally, a high oxide-fixed trap density meaningfully influences Vth (negative shifting) and penalizes the device drain current over the whole explored voltage range.