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The reverse breakdown characteristics of 4H-SiC Junction Barrier Schottky (JBS) rectifiers adopting the different floating limiting rings (FLRs) termination structures are experimented and analyzed under the repetitive avalanche current stress. The experimental results indicate that the breakdown voltage (BV) shift of the device after the repetitive avalanche current stress is highly dependent on the FLRs design, which determines the distributions of the surface electric field and avalanche current at avalanche condition. It is proved that the uniform surface electric field distribution of the FLRs structure at avalanche condition is helpful for the device achieve to achieve better BV shift robustness on the repetitive avalanche current stress. Additionally, the FLRs structure, which has smaller S1 and enough Nr, can present both higher BV and excellent BV shift robustness on the repetitive avalanche current stress.

The dynamic avalanche reliability of 1200-V silicon carbide (SiC) power metal-oxide semiconductor field-effect transistors (MOSFETs) is studied in this article. The unclamped inductive switching (UIS) tests are conducted to locate failure points. An optimized thermal network model with the definition of the material above the epitaxial layer is used to simulate the avalanche process of SiC MOSFETs. The simulation and experiment results are matched, which verifies the validity of this model. Further simulation results show that a slight change in the doping profile of the p-well region will make the avalanche capability significantly different. Then, the effect of the deviation in cell parameters on the avalanche capability is studied by multicell simulation. The results demonstrate that uneven distribution of internal parameters makes the parasitic bipolar junction transistor (BJT) of some cells turn-on first, causing a significant concentration of current and heat in a very short time, and eventually forming hot spots often observed in failed devices.

The bandgap of epitaxial graphene thermally grown on 4H–SiC(0001) can be widened via a novel charge transfer mechanism by modifying the buffer layer and surface of SiC with substrate doping before epitaxial graphene growth. High-resolution photoemission spectroscopy base on synchrotron radiation reveal that the bandgap broadening of epitaxial graphene is attributed to modification of buffer layer between epitaxial graphene and the substrates, and both donor-acceptor and bulk atoms injected in the SiC make the bandgap of EG on those substrates broaden. This novel bandgap broadening mechanism via substrates doping will provide a simple and effective approach to nondestructively broad the bandgap of epitaxial graphene for future electronics application.

This paper reports the demonstration of a high performance 4H-SiC floating junction junction barrier Schottky (FJ_JBS) rectifier with a 30μm, 6×1015 cm-3-doped epitaxial layer. Extensive simulations have been performed to design, optimize and analyze the structure of the FJ_JBS rectifier. The fabricated FJ_JBS shows that breakdown voltage (BV) and differential Ron,sp are 3.4 kV, yielding the highest BV value reported for 4H-SiC FJ diodes, and 5.67 mΩ·cm2, respectively. Compared with the conventional JBS, the BV value of FJ_JBS increases by 33.3% and the Ron,sp only slightly rises by 6.2%. The corresponding Baliga figure-of-merit (BFOM) (4 BV2/Ron_sp) of this FJ_JBS diode is 8.16 GW/cm2.

The properties of 4H–SiC/Ni/Ti/Al/W metal contacts on n-type and p-type ion-implanted 4H–SiC layers are studied in this paper, with the aim of realizing simultaneous ohmic contact formation. The thickness of the Al film and the alloying temperature are analyzed. Specific contact resistances of 8 × 10−4 Ω cm2 and 4.1 × 10−5 Ω cm2 were achieved with multi-metal layer Ni/Ti/Al/W (80/30/110/50 nm) for n-type and p-type 4H–SiC, respectively, at an annealing temperature of 750 °C. This is for first time at such a low annealing temperature that ohmic contacts have been reported to simultaneously form on n-type and p-type 4H–SiC with satisfactory specific contact resistances. Samples were characterized using AFM, XRD, AES and TEM, and the results indicate that the presence of the W top layer facilitates lowering the surface roughness and accumulating elemental Ni and Al on the SiC side during annealing, which benefits the formation of the ohmic contacts.

In this paper, Pt/TaSi2/Ni/Ti/Ni/SiC and Pt/Ti/SiC simultaneous ohmic contacts to n-type and p-type 4H-SiC are studied. The thermal stability and electrical characteristics of the ohmic contacts are investigated and compared after being aged at 500 °C for 300 h in air. The n- and p-type Pt/Ti/SiC ohmic contact failed after 100 h and after 200 h, respectively. While the Pt/TaSi2/Ni/Ti/Ni/SiC samples exhibits a good thermal stability and high temperature electrical characteristics, with a relatively small increase of the specific contact resistance (SCR) in the initial 50 h and then remains stable in the rest of the thermal aging duration. SEM analysis reveals that the surface morphologies of Pt/TaSi2/Ni/Ti/Ni/SiC samples keep smooth and stable during the aging process. According to AES analysis, the main reason of electrical characteristics degradation is the oxidation on the metal/4H-SiC interface during the aging process. Also, at the expense of the TaSi2 layer oxidization, the diffusion rate of oxygen atoms towards the SiC are slowed down, and therefore, the metal/4H-SiC interface quality was not affected by oxidation problems and extending the life of ohmic contact in air at 500 °C. Experimental results indicate that the Pt/TaSi2/Ni/Ti/Ni/SiC simultaneous ohmic contacts to both n- and p-type SiC are promising to be used for high temperature and harsh environment SiC-based devices.

In this paper the effects of 5 MeV proton irradiation on nitrided SiO2/4H-SiC metal&ndash, oxide&ndash, semiconductor (MOS) capacitors are studied in detail and the related mechanisms are revealed. The density of interface states (Dit) is increased with the irradiation doses, and the annealing response suggests that the worse of Dit is mainly caused by displacement effect of proton irradiation. However, the X-rays photoelectron spectroscopy (XPS) measurement shows that the quantity proportion of breaking of Si&equiv, N induced by displacement is only 8%, which means that the numbers of near interface electron traps (NIETs) and near interface hole traps (NIHTs) are not significantly changed by the displacement effect. The measurements of bidirectional high frequency (HF) C-V characteristics and positive bias stress stability show that the number of un-trapped NIETs and oxide electron traps decreased with increasing irradiation doses because they are filled by electrons resulted from the ionization effect of proton irradiation, benefiting to the field effective mobility (&mu, FE) and threshold voltage stability of metal&ndash, semiconductor field-effect transistors (MOSFETs). The obviously negative shift of flat-band voltage (VFB) resulted from the dominant NIHTs induced by nitrogen passivation capture more holes produced by ionization effect, which has been revealed by the experimental samples with different nitrogen content under same irradiation dose.

In this letter, planar floating limiting rings (FLRs) and trench FLRs with different trench depths for the 4H-SiC junction barrier Schottky (JBS) rectifiers are analyzed and compared with simulations and experiments. Compared with the planar FLRs, the experimental results present that the first ring spacing window that termination efficiency exceeds 80% of the parallel plane breakdown voltage (BV) can be widened and termination area can be reduced at the same BV by adopting the trench FLRs. The simulations also indicate that there is an optimal trench depth for the trench FLRs and a smaller sidewall angle can achieve better device performance. Additionally, the repetitive avalanche current stress measurements imply that the trench FLRs has better robustness regarding the BV shift, achieving better device reliability.

In this paper, a comparison of different floating junction structure underneath the termination region FJt for 4H-SiC FJ_JBS is performed by simulations and experiments. The simulated results indicate that the optimized dose of FJt is different when the different FJt structures are chosen, which is resulting from different work mechanism. The experimental results show that the breakdown voltage of FJ_JBS with discontinuous floating junction structure underneath the termination region is 2.9 kV. For comparison, the FJ_JBS with continuous floating junction structure without fixed outer boundary underneath the termination only achieves a breakdown voltage of 2.05 kV, which validates the simulation results.