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Selective nitrogen doping of 4H-SiC by epitaxial growth using TaC as the hightemperature mask has been demonstrated. Nomarski optical microscopy and scanning electron microscopy (SEM) were used to characterize selective growth of SiC. In addition, 250-µm, square-shaped, p-n junction diodes by selective n-type epitaxial growth on a p-type epilayer were fabricated. The refilled fingers with different width were designed to vary the periphery/area (P/A) ratio. The effects of P/A ratio on the current-voltage (J-V) characteristics have been investigated. The ideality factor extracted from J-V characteristics is Ϸ2 at a temperature range of 25-275°C, which indicates that the ShockleyRead-Hall recombination is the dominant mechanism in the conduction region. The reverse leakage current does not show dependence on P/A ratio for trench-refilled diodes. The room-temperature reverse leakage-current density at 100 V is less than 3.5 ϫ 10 Ϫ7 A/cm 2 for all diodes. Also, the reverse leakage current does not increase significantly with temperature up to 275°C. The breakdown voltages measured at room temperature are about 450 V and 400 V for diodes without and with fingers, respectively.

The switching versus forward conduction performance tradeoffs of lOkV 4H-SiC PiN diodes are optimized using emitter injection control. Experimental results show superior switching performance with up to a 40% reduction in critical recovery parameters such as Qrr and JRP, while simulations indicate a better performance tradeoff than conventional PiN diodes in the presence of sufficiently long drift layer lifetime.

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