High Temperature Characteristics of NO Annealed P-Channel 4H-SiC MOSFET

Abstract

Abstract Body: Superior material qualities of 4H-SiC such as wide bandgap, high thermal conductivity, and large breakdown electric field make devices capable of operating with high power at high temperature. In this work, the behavior of p-channel 4H-SiC metal-oxide-semiconductor field-effect transistor (MOSFET), where holes are the channel charge carriers; has been investigated. The experimental results confirm that post oxidation Nitric Oxide (NO) annealing reduces SiO2/4H-SiC interface trap densities (Dit) in the upper half of the 4H-SiC bandgap as widely reported. In addition, Dit is also significantly reduced in the lower half, which is critical for p-channel MOSFETs. This result is corroborated by capacitance-voltage (CV) measurements conducted on p- and n-type 4H-SiC MOS capacitors from room temperature to 300°C, as well as under UV illumination, which allows estimation of the Dit profile throughout the large 4H-SiC bandgap. Thereafter, p-channel 4H-SiC MOSFETs were fabricated and measured from room temperature through 300°C. The MOSFETs without NO annealing turn on at very large negative voltages with high dielectric leakage currents, making it difficult to get reliable high temperature data. In contrast, the NO annealed MOSFETs turn on at a much lower voltage, with low leakage, consistent with the reduction of Dit due to NO annealing. With the rise of temperature, the threshold voltage drops as the number of occupied interface traps reduce with the increase of temperature. However, the temperature dependence of the hole channel mobility is not obvious from these measurements. The weak temperature dependence can be explained considering the behavior of the phonon and Coulomb scattering components. The phonon scattering limited hole mobility reduces from ~120 cm2/Vs at room temperature to less than 25 cm2/Vs at 300°C in lightly doped bulk p-type 4H-SiC. On the other hand, the Coulomb scattering limited surface hole mobility increases weakly with temperature. The competition between the two mechanisms increases at higher temperatures and the overall field-effect mobility shows an almost temperature-independent behavior in the 25°C - 300°C range. While NO annealing realizes high temperature operation, the negative bias temperature instability (NBTI) is a major shortcoming. This is a result of hole injection and trapping in the oxide under high temperature and negative bias stress. In this presentation, the results from the NBTI experiments will be reported and the main mechanisms related to high temperature NBTI will be discussed. The authors gratefully acknowledge the funding support from US Army Research Laboratory grant ARMY-W911NF-18-2-0160 and National Renewable Energy Laboratory/ US Department of Energy grant NREL-AHL-9-92362-01.