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8-15 kV High Temperature SiC PiN and Schottky Rectifiers
Keywords: SiC, Ultra-High Voltage, kilovolts
This paper reports on ultra-high voltage, >15 kV SiC PiN rectifiers exhibiting >95% of the avalanche rating and 115 V/µm. Excellent stability of on-state voltage drop (VF) is displayed by 5.76 mm2 and large-area, 41 mm^2 PiN rectifiers, when continually biased at high current densities for several days. The impact of carrier lifetime on the device performance for SiC bipolar devices with ultra-thick (≥100 µm) base layers is investigated by comparing I-V-T characteristics of SiC PiN rectifiers fabricated on 100 µm and 130 µm thick epilayers. PiN rectifiers are fabricated on 130 µm thick/6-7x10^14 cm-3 doped n- epilayers grown on n+ 4H-SiC substrates. The p+ anode layer is 2 µm thick with a doping of 1 x 10^19 cm-3. PiN rectifiers with chip sizes of 5.76 mm2 and 41 mm2 are reported in this paper. Selected devices are packaged in special test coupons with 15 kV stand-off capability. The onset of sharp avalanche breakdown at 15 kV is observed on several PiN rectifiers, with extremely low-leakage currents preceding the breakdown voltage. An on-state voltage drop (VF) of 6 V is measured on the 5.76 mm2 rectifiers at 100 A/cm2 and 25 °C, which reduces to 4 V at 225 °C. Likewise, the 41 mm2 rectifiers also exhibit a negative temperature co-efficient of VF, – 4.1 V at 25 °C (10 A) and 3.3 V at 175 °C. The negative temperature co-efficient of VF is due to a drop in on-resistance from 15.5 mΩ-cm2 at 25 °C to 8 mΩ-cm2 at 225 °C. Significantly lower on-resistance and a softer temperature dependence was observed for PiN rectifiers fabricated on 100 µm epilayers[ ], indicating that the carrier lifetimes in the 130 µm thick n- epilayers although high (in the range of 3-9 µs) are not sufficient for complete conductivity modulation of the entire base layer. Wafer maps of VF obtained from electrical measurements are correlated with wafer maps of carrier lifetimes measured by microwave photoconductive decay (µ-PCD). The stability of the on-state characteristics is evaluated by subjecting 5.76 mm2 and 41 mm2 PiN rectifiers to DC currents of 0.8 A (100 A/cm2) and 10 A (40 A/cm2), respectively for >50 hours at a controlled base-plate temperature of 25 °C. After an initial stabilization period of 5-10 hours, the VF shows an excellent stability within 50 mV for the remainder of the test for both small and large-area PiN rectifiers. Hard-switching measurements at 10 kV by pairing the 15 kV rectifiers with SiC BJTs, correlation of optically (µ-PCD) and electrically (OCVD) measured carrier lifetime with I-V-T characteristics, and correlation of VF drift stability with basal plane dislocation (BPD) density investigations on stressed devices will be presented in the full paper.
Ranbir Singh,
GeneSiC Semiconductor Inc.
Dulles, VA

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