Materials Science Forum Vols. 717-720

Abstract: The transient electrical characteristics of the forward recovery and reverse recovery characteristics of lifetime-controlled high blocking voltage 4H-SiC pin diodes by electron irradiation are investigated. Even at a heavy electron dose of 1×1014 cm-2, the forward voltage overshoot of a 4H-SiC pin diode is lower than that of a 2 kV/100 A class Si fast diode. As for the reverse recovery characteristics, small reverse recovery current and fast reverse recovery time are obtained by electron irradiation. The reduction ratio of recovery loss can therefore exceed the increase ratio of steady-state loss by electron irradiation.

Abstract: This paper reports the fabrication and electrical characterization of PiN diodes on an on-axis grown epitaxial layer. TCAD simulations have been performed in order to design their architecture. Some of these diodes have a breakdown voltage around 600 V. A comparison is made with similar diodes fabricated on off-cut grown layers. Computer simulations are used to explain lower breakdown voltage than those expected.

Abstract: Breakdown characteristics of 4H-SiC PiN diodes with various JTE structures have been investigated. By combining two-zone JTE and Space-Modulated JTE (SM-JTE), a breakdown voltage over 15 kV, corresponding to about 93 % of the parallel-plane breakdown voltage, was realized. The window of optimum JTE dose to obtain high breakdown voltage was widened, which indicates the robustness to the deviation of JTE dose. By comparing the breakdown voltage obtained by simulation and experimental results, impacts of the charge near the SiO₂/SiC interface are discussed.

Abstract: The multi-zone junction termination extension (MJTE) is a widely used edge termination technique for achieving high voltage SiC devices. It is commonly implemented with multiple lithography and implantation events. In order to reduce process complexity, cycle time, and cost, a single photolithography and single implant MJTE technique has been successfully developed. The method utilizes a pattern of finely graduated oxide windows that filter the implant dose and create a graded MJTE in a single implant and single photolithography step. Based on this technique, 6 kV / 0.09 cm2 PiN diodes were fabricated utilizing a 120-zone single-implant JTE design. This novel single-implant MJTE design captures 93% of the ideal breakdown voltage and has comparable performance and yield to a baseline three implant process.

Abstract: Integration of patterned ballast resistance into the anode of SiC PiNs is a solution to the dilemma of negative dV_f /dT for such diodes. In fabricated 4H-SiC PiN diodes, we demonstrate a cross-over from negative to positive temperature coefficient for current densities as low as 80 A/cm². Adjusting the percentage of the patterned anode area, the positive or neutral dV_f /dT can be achieved over a wide current-density range without substantial penalty in the forward voltage drop. This characteristic is crucial for high-power SiC packages with ganged-parallel rectifier arrays.

Abstract: The fabrication of a fully ion-implanted and microwave annealed vertical p-i-n diode using high purity semi-insulating 4H-SiC substrate has been demonstrated for the first time. The thickness of the intrinsic region is the wafer thickness 350 µm. The anode and cathode of the diode have been doped with Al and P, respectively, to concentrations of few times 10²⁰ cm^-3 by ion implantation. The post implantation annealing has been performed by microwave heating the samples up to 2100°C. The device rectifying behavior indicates that a carrier modulation takes place in the bulk intrinsic region.

Abstract: The forward voltage drops of pin diodes with the carbon implantation process or thermal oxidation process using a drift layer of 120 μm thick are around 4.0 V and are lower than those with the standard process. The reverse recovery characteristics of diodes with the standard process or carbon implantation at room temperature show almost the same tendency. In the reverse recovery characteristics at 250 oC, pin diodes with carbon implantation process, however, have the longer reverse recovery time than those with the standard process. These characteristics indicate that a recombination path other than the bulk carrier lifetime, such as the interfaces or the surface recombination, becomes dominant in the reverse recovery characteristics at room temperature.

Abstract: With the recent technological advances in 4H-SiC PiN diode fabrication, simulation tools which enable the accurate and rapid prediction of losses of such devices in power electronics circuits will be increasingly sought-after. To this end, a physical electro-thermal model of the 4H-SiC PiN diode has been developed, which facilitates device optimization for power circuit applications. The performance of this model has been compared with both finite element simulations and experimental results; good matching for both switching and conduction characteristics has been observed.

Abstract: Recent progress in the field of silicon carbide sensor technology, such as wireless communications and sensors, has demonstrated the need for a resilient energy supply as an alternative to conventional batteries. Previous work has shown that silicon carbide is an effective energy harvester of UV light in high temperature and hostile environments. Until now however, there has been little work undertaken to assess the long-term effects of elevated temperature on such devices. Although it is understood that silicon carbide is unaffected by long-term temperature exposure below 400 °C, there has been little research into the overall device response and how changes in contact metallisation affect the photovoltaic behaviour.

Abstract: The photoconductive semiconductor switches (PCSS) were fabricated on V-doped semi-insulating 6H-SiC. We studied the effect of surface morphology on the on-state resistance of SiC PCSS. The SiC wafers with quite similar physical properties were processed by mechanical polishing, chemical mechanical polishing and H2 etching for producing different surface morphologies. All the SiC PCSS were excited by a 355 nm laser with a frequency of 10 Hz and a pulse intensity of 132 μJ/mm². We found that the surface morphology had an obvious effect on the on-state resistance. The PCSS fabricated on mechanical polished SiC wafer with an average surface roughness (rms) of 1.0 nm showed the largest on-state resistance of 45.6 ohms, while a low value of 13.3 ohms was observed for the wafer processed by H2 etching at high temperature of 1550 °C.