2054 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 49, NO. 11, NOVEMBER 2002 High-Power 4H-SiC JBS Rectifiers Ranbir Singh, D. Craig Capell, Allen R. Hefner, Fellow, IEEE, Jason Lai, Senior Member, IEEE, and John W. Palmour, Member, IEEE Abstract—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-i-n 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-i-n 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. Index Terms—Junction Barrier Schottky (JBS), merged p-i-n Schottky, rectifier, reverse-recovery, Schottky, silicon carbide (SiC), ultrafast diodes. I. INTRODUCTION P OWER devices made with silicon carbide (SiC) are ex- pected to show great performance advantages as compared to those made with other semiconductors. This is primarily be- Manuscript received March 15, 2002; revised August 30, 2002. This work was supported by the Defense Advanced Research Projects Agency’s (DARPA’s) MEGAWATT Program under Office of Naval Research Contract N00014-98-C- 0191, monitored by G. Campisi and D. Radack. Contributions of the National Institute of Standards and Technology are not subject to U.S. copyright. The review of this paper was arranged by Editor M. A. Shibib. R. Singh, D. C. Capell, and J. W. Palmour are with Cree Inc., Durham NC 27703 USA (e-mail: ranbir_singh@cree.com). A. R. Hefner is with the National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899 USA. J. Lai is with the Virginia Polytechnic Institute and State University, CPES, Blacksburg, VA 24061-0111 USA. Digital Object Identifier 10.1109/TED.2002.804715 cause 4H-SiC has an order of magnitude higher breakdown elec- tric field (2–4 10 V/cm) than Si and GaAs and an electron mobility only 20 lower than Si. A high breakdown electric field allows the design of SiC power devices with thinner and higher doped voltage-blocking layers. 4H-SiC unipolar devices are expected to replace Si bipolar switches and rectifiers in the 600–3000 V range in the future. Generally speaking, there are three classes of power rectifiers: 1) Schottky diodes, which offer extremely high switching speed but suffer from lower blocking voltage and high leakage current; 2) p-i-n diodes, which offer high-voltage operation and low- leakage current, but show reverse-recovery charge during switching; 3) Junction Barrier Schottky (JBS) diodes, which offer Schottky-like on-state and switching characteristics and p-i-n-like off-state characteristics. In conventional high-voltage ( 600 V) circuits using Si p-i-n diodes, the primary source of power loss is the dissipation of reverse-recovery charge during the turn-off of the rectifier. The switches used in these inverter and converter circuits have to be de-rated substantially to account for this large heat dissipation. The 4H-SiC JBS diode offers nearly zero reverse-recovery charge. This allows the design of packages with much lower thermal dissipation requirements for both the rectifier and the switch. The on-state performance of a 4H-SiC JBS diode is expected to be comparable to that of a Si p-i-n diode. The on-state voltage drop at sufficiently high current densities for a unipolar device (like Schottky/JBS diode) depends on the resistive voltage drop in the low-doped drift region. To achieve a high blocking voltage, the drift region doping must be reduced and its thickness must be increased. This leads to a high on-state voltage drop for a high-voltage unipolar device. In the case of a bipolar device (like p-i-n diode), minority carrier injection into the low-doped drift region during on-state operation results in very low voltage drop even for very high breakdown voltage rated devices. However, in the case of a bipolar device, the device does not turn ON until a forward bias equivalent to the bandgap of the device is applied. Therefore, the breakdown voltage rating for which the on-state performance of a p-i-n diode (a bipolar device) is superior to that of a Schottky/JBS diode (a unipolar device) for equivalent sized die depends on the material used for its fabrication. For Si, this limit is approximately 200 V; for GaAs, it is approximately 500 V; and for 4H-SiC it is approximately 3000 V. II. BASIC OPERATION AND DESIGN OF 4H-SIC JBS DIODES A cross section of a 4H-SiC JBS rectifier operating in the forward and reverse bias is shown in Fig. 1. A JBS diode consists 0018-9383/02$17.00 © 2002 IEEE