Materials Science Forum Vols. 483-485

Abstract: A 4H-SiC 600 V class Deep-Implanted gate Vertical JFET (DI-VJFET) is examined. The DI-VJFET exhibited a specific on-resistance of 13 mΩcm2, drain current of 5 A, and a blocking-voltage of 600 V. In this paper, the very high temperature dependence (R.T.~ 400 oC) of the I-V characteristics is measured and the dominant factor of the on-resistance and the blocking-voltage is discussed. Moreover, the switching waveform of SiC DI-VJFET with SiC SBD is measured by using a half bridge, double-pulse circuit with inductive load at R.T. and 200 oC. The turn-off time is 300 ns at an inductance of 4 mH and an external gate resistance of 100 Ω.

Abstract: 4H-SiC vertical depletion-mode trench JFETs were fabricated, packaged, and then irradiated with either 6.8 Mrad gamma from a 60Co source, a 9x1011 cm-2 dose of 4 MeV protons, or a 5x1013 cm-2 dose of 63 MeV protons. 4H-SiC Schottky diodes were also fabricated, packaged and exposed to the same irradiations. The trench VJFETs have a nominal blocking voltage of 600 V and a forward current rating of 2 A prior to irradiation. On-state and blocking I-V characteristics were measured after irradiation and compared to the pre-irradiation performance. Devices irradiated with 4 MeV proton and gamma radiation showed a slight increase in on resistance and a decrease in leakage current in blocking mode. Devices irradiated with 63 MeV protons, however, showed a dramatic decrease in forward current. DLTS measurements were performed, and the results of these measurements will be discussed as well.

Abstract: The current gain (b) of 4H-SiC BJTs as function of collector current (IC) has been investigated by DC and pulsed measurements and by device simulations. A measured monotonic increase of b with IC agrees well with simulations using a constant distribution of interface states at the 4H-SiC/SiO2 interface along the etched side-wall of the base-emitter junction. Simulations using only bulk recombination, on the other hand, are in poor agreement with the measurements. The interface states degrade the simulated current gain by combined effects of localized recombination and trapped charge that influence the surface potential. Additionally, bandgap narrowing has a significant impact by reducing the peak current gain by about 50 % in simulations.

Abstract: The letter presents a set of design curves that relate the open-base breakdown voltage BVCEO to the open emitter breakdown voltage BVCBO for 4H (0001 and 11-20 orientations) and 6H SiC NPN and PNP Bipolar Junction Transistors. We also present design curves pertaining to the variation of BVCEO with base doping and minority carrier diffusion length in the base for (0001) 4H-SiC BJTs for a 4x1015 cm-3 doped and 12µm thick drift layer for both NPN and PNP BJTs.

Abstract: 1000 V Bipolar Junction Transistor and integrated Darlington pairs with high current gain have been developed in 4H-SiC. The 3.38 mm x 3.38 mm BJT devices with an active area of 3 mm x 3 mm showed a forward on-current of 30 A, which corresponds to a current density of 333 A/cm2, at a forward voltage drop of 2 V. A common-emitter current gain of 40 was measured on these devices. A specific on-resistance of 6.0 mW-cm2 was observed at room temperature. The onresistance increases at higher temperatures, while the current gain decreases to 30 at 275°C. In addition, an integrated Darlington pair with an active area of 3 mm x 3 mm showed a collector current of 30 A at a forward drop of 4 V at room temperature. A current gain of 2400 was measured on these devices. A BVCEO of 1000 V was measured on both of these devices.

Abstract: 4H-SiC BJTs were fabricated using epitaxial regrowth instead of ion implantation to form a highly doped extrinsic base layer necessary for a good base ohmic contact. A remaining p+ regrowth spacer at the edge of the base-emitter junction is proposed to explain a low current gain of 6 for the BJTs. A breakdown voltage of 1000 V was obtained for devices with Al implanted JTE.

Abstract: The paper presents a study of the different aspects of the temperature dependent performance of a 4H-SiC epi-emitter Bipolar Junction Transistor particularly the low temperature performance. Some critical device physics related factors that affect the forward active performance of the device are explored and the device behavior is modeled up to 100K. We present for the first time the experimental low-temperature (down to 100K) performance of 4H-SiC epi-emitter BJTs and the determination of the temperature beyond which the current gain starts to increase with temperature. We have also corroborated these results with 2-dimensional device simulations.

Abstract: We present the results of a simulation study on the behaviour of 3C-SiC bipolar transistors fabricated using a 6H-SiC heterojunction emitter. We show that despite the potential barrier originating in the discontinuity of the conduction bands, that npn devices offer a higher common emitter gain in comparison to pnp devices. The base voltage corresponding to the maximum gain of the device is controlled by the tunnelling of carriers across the collector-base junction and is different for both npn and pnp devices.