High-Voltage (2.8 kV) Implantation-Free 4H-SiC BJTs With Long-Term Stability of the Current Gain

In this paper, implantation-free 4H-SiC bipolar junction transistors (BJTs) with a high breakdown voltage of 2800 V have been fabricated by utilizing a controlled two-step etched junction-termination extension in the epitaxial base layer. The small-area device shows a maximum direct-current (dc) gain of 55 at J_C = 0.33 A (J_C = 825 A/cm²) and V_CESAT = 1.05 V at I_c = 0.107 A that corresponds to a low specific ON-state resistance of 4 mΩ · cm². The large-area device has a maximum dc gain of 52 at J_C = 9.36 A (J_C = 289 A/cm²) and V_CESAT = 1-14 V at I_c = 5 A that corresponds to a specific ON-state resistance of 6.8 mΩ · cm². In addition, these devices demonstrate a negative temperature coefficient of the current gain (β = 26 at 200 °C) and a positive temperature coefficient of the specific ON-state resistance (R_ON = 10.2 mΩ · cm² at 200 °C). The small-area BJT shows no bipolar degradation and a low-current-gain degradation after a 150-h stress of the base-emitter diode with a current level of 0.2 A (J_E = 500 A/cm²). Furthermore, the large-area BJT shows a V_CE fall time of 18 ns during turn-on and a V_CE rise time of 10 ns during turn-off for 400-V switching characteristics.