Design, fabrication and characterization of high voltage 4H-silicon carbide junction rectifiers for power switching applications

As material issues are addressed, proper device design promises to play a critical role in the commercialization of 4H-SiC bipolar diodes. This thesis investigates promising techniques to improve the switching characteristics of 4H-SiC bipolar diodes using numerical simulations and fabricated prototypes. Two approaches, emitter injection efficiency tailoring and novel structures, Epitaxial Refill Static Shielded Diodes (ER-SSD), are experimentally demonstrated for 10kV applications.; Baseline epitaxial and implanted anode PiN diodes, are fabricated using 110mum thick, lightly doped drift layers. The low forward voltage drop, VF=4.0-4.2V (JF=100A/cm2), of the epi-anode diodes shows significant conductivity modulation, further evidenced by diode switching characteristics. A reverse recovery charge density of Qrr ≈ 11muC/cm2 is observed when switched from JF=100A/cm 2 at room temperature and increases to Qrr ≈ 24muC/cm 2 at T=225°C.; The new ER-SSD use shallow implanted P-channels and epi-P+ regions to tailor the stored charge in the drift region under forward bias. Simulated tradeoffs illustrate superior switching performance, reducing Q rr by up to 30% and the reverse peak current density, JRP by 50% compared to a PiN. The improved switching performance is also evidenced by the first reported 4H-SiC ER-SSD showing over a 50% lower Qrr and JRP than co-fabricated PiN diodes, while exhibiting forward voltage drops of VF=5-6V at JF=100A/cm2.; PiN diodes with reduced emitter injection efficiency are also used to improve switching performance. Diodes with thin (0.25mum) P+ anodes achieve up to 40% lower Qrr and JRP, compared to the baseline PiN design. The emitter controlled diodes also exhibit the attractive characteristic of a positive temperature dependence of forward voltage drop at typical operating bias, with a room temperature VF=4.5V increasing by less than 10% at T=200°C.; High voltage blocking is achieved using a novel Multi-zone, Single Implant Junction Termination Extension (MZ-SI JTE). The new termination promises good performance sensitivity to process variations while decreasing fabrication cycle time. Simulation results show over 90% of the one-dimensional limit can be achieved with the target design and the desired 10kV blocking is maintained with up to +/-50% variation in JTE doping. Fabricated devices demonstrate the effectiveness of the MZ-SI JTE with diode breakdown reaching the 10kV design goal.