This paper reports the design, fabrication and high temperature characteristics of 1 mm 2 , 4 mm 2 and 9 mm 2 4H-SiC p-in rectifiers with 6 kV, 5 kV, and 10 kV blocking voltage, respectively. These results were obtained from two lots in an effort to increase the total power levels on such rectifiers. An innovative design utilizing a highly doped p-type epitaxial Anode layer and junction termination extension (JTE) were used in order to realize good on-state as well as stable blocking characteristics. For the 1 mm 2 and 4 mm 2 rectifier, a forward voltage drop of less than 5 V was observed at 500 A/cm 2 and the peak reverse recovery current shows a modest 50% increase in the 25 C to 225 C temperature range. On the 10 kV, 9 mm 2 rectifier, a forward voltage drop of less than 4.8 V was observed at 100 A/cm 2 in the entire 25 C to 200 C temperature range. For this device, the reverse recovery characteristics show a modest 110% increase in the peak reverse recovery current from 25 C to 200 C. A dramatically low rr of 3.8 C was obtained at a forward current density of 220 A/cm 2 at 200 C for this ultra high voltage rectifier. These devices show that more than three orders of magnitude reduction in reverse recovery charge is obtained in 4H-SiC rectifiers as compared to comparable Si rectifiers.
This paper reports the detailed design, fabrication, and characterization of two sets of high-power 4H-Silicon Carbide (4H-SiC) Junction Barrier Schottky (JBS) diodes-one with a 1500-V, 4-A capability and another with 1410-V, 20-A capability. Two-dimensional (2-D) device simulations show that a grid spacing of 4 m results in the most optimum trade-off between the on-state and off-state characteristics for these device ratings. JBS diodes with linear and honeycombed p + grids, Schottky diodes and implanted p-in diodes fabricated alongside show that while 4H-SiC JBS diodes behave similar to Schottky diodes in the on-state and switching characteristics, they show reverse characteristics similar to p-in diodes. Measurements on 4H-SiC JBS diodes indicate that the reverse-recovery time () and associated losses are near-zero even at a high reverse dI/dt of 75 A/ s. A dc/dc converter efficiency improvement of 3-6% was obtained over the fastest, lower blocking voltage silicon (Si) diode when operated in the 100-200 kHz range. The 1410-V/20-A JBS diodes were evaluated for both hard-and soft-switching applications. Experimental results indicate that their conduction characteristics are comparable with the Si diode counterpart, but the switching characteristics are far superior. When applied to hard-switching choppers, it reduces not only the reverse-recovery loss, but also the main switch turn-on loss. Using the MOSFET as the main switching device, the combination of switch turn-on loss and diode reverse-recovery loss shows more than a 60% reduction. When applied to soft-switching choppers, the SiC JBS diode is used as the auxiliary diode to avoid the voltage spike during auxiliary branch turn-off. With the conventional ultrafast reverse-recovery Si diode, a voltage spike exceeds the switched-voltage transition by 100% and the auxiliary circuit requires additional voltage clamping or snubbing to avoid over-voltage failure. With the SiC JBS diode, however, the voltage spike is reduced to less than 50% of the switched-voltage transition and the additional voltage clamping circuit can be eliminated. Savings in soft-switching choppers using SiC JBS diodes can be realized in size and weight reduction, energy loss reduction, and reduced packaging complexity.
Heavily doped p-type layers obtained by implanting aluminum near its solubility limit (∼2×1020Al∕cm3) in 4H-SiC are characterized as a function of the implant and anneal temperatures. For a typical implant temperature of 650°C, Al activation rates of ∼6%–35% are obtained for anneals from 1600 to 1750°C, respectively. For higher temperature implants at 1000°C, the Al activation rates are significantly improved, approaching ∼100% for the same anneal temperatures, with a best p-type resistivity of ∼0.20Ωcm. For SiC device fabrication, these results demonstrate that by using higher Al implant temperatures, lower anneal temperatures can be used while obtaining close to 100% Al activation.
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