Enhanced Forward Bias Operation of 4H-SiC PiN Diodes Using High Temperature Oxidation
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Enhanced Forward Bias Operation of 4H-SiC PiN Diodes Using High Temperature Oxidation Craig A. Fisher1, Michael R. Jennings1, Yogesh K. Sharma1, Dean P. Hamilton1, Stephen M. Thomas1, Fan Li1, Peter M. Gammon1, Amador Pérez-Tomás2, Susan E. Burrows3 and Philip A. Mawby1 1
School of Engineering, University of Warwick, Coventry, CV4 7AL, UK. Institut Català De Nanociència i Nanotecnologia, 08193, Bellaterra, Barcelona, Spain. 3 Department of Physics, University of Warwick, Coventry, CV4 7AL, UK.
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ABSTRACT In this paper, high temperature (>1400°C) thermal oxidation has been applied, for the first time, to 4H-SiC PiN diodes with thick (110 µm) drift regions, for the purpose of increasing the carrier lifetime in the semiconductor. PiN diodes were fabricated using 4H-SiC material that had undergone thermal oxidation performed at 1400°C, 1500°C and 1600°C, then were electrically characterized. Forward current-voltage (I-V) measurements showed that thermally oxidized PiN diodes exhibited considerably improved electrical characteristics, with devices oxidized at 1500°C having a forward voltage drop (VF) of 4.15 V and a differential on-resistance (Ron,diff) of 8.9 mΩ-cm2 at 100 A/cm2 and 25°C. Compared to typical control sample PiN diode characteristics, this equated to an improvement of 8% and 23% for VF and Ron,diff, respectively. From analysis of the reverse recovery characteristics, the carrier lifetime of the PiN diodes oxidized at 1500°C was found to be 1.05 µs, which was an improvement of around 30% compared to the control sample PiN diodes. INTRODUCTION Due to its excellent electrical and thermal properties, 4H-silicon carbide (SiC) is widely tipped to be the successor to silicon (Si) for high voltage (>3kV) power electronics [1]. These superior material properties of 4H-SiC include a high critical electric field of ~3 MV/cm (around 10 times higher than Si), a high thermal conductivity of ~4.5 W/cm-K (around 3 times that of Si) and an energy band gap of 3.26 eV (also around 3 times that of Si). From a practical perspective, these material advantages mean that, compared to Si, 4H-SiC offers improved voltage blocking performance for a given drift region thickness and doping; this in turn means that shorter carrier lifetimes are sufficient to fully modulate the drift region in bipolar devices, thus also yielding much improved transient performance. Furthermore, the higher thermal conductivity and wider energy band gap are both beneficial for device operation under high power density and high operating temperatures, two increasingly important factors for future power electronics systems. Despite the obvious advantages of 4H-SiC for power electronics devices, the material has not yet fulfilled its true potential, and, to date, only unipolar devices (Schottky diodes and MOSFETs) are commercially available, up to a maximum voltage rating of 1.7 kV [2]. At higher voltages, MOSFETs suffer from increased conduction losses; as such, the use of bipolar devices, such as IGBTs, thyristors and PiN diodes, is preferable for high
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