Evaluation of termination techniques for 4H-SiC PiN diodes and trench JFETs

An investigation concerning suitable termination techniques for 4H-SiC trench JFETs is presented. Field plates, p+ floating rings and junction termination extension techniques are used to terminate 1.2kV class PiN diodes. The fabricated PiN diodes evaluated here have a similar design to trench JFETs. Therefore, the conclusions for PiN diodes can be applied to JFET structures as well. Numerical simulations are also used to illustrate the effect of the terminations on the diodes' blocking mode behaviour.

Switching performance of epitaxially grown normally-off 4H-SiC JFET

Static and dynamic behavior of the epitaxially grown dual gate trench 4H-SiC junction field effect transistor (JFET) is investigated. Typical on-state resistance Ron was 6-10mΩcm2 at VGS = 2.5V and the breakdown voltage between the range of 1.5-1.8kV was realized at VGS = -5V for normally-off like JFETs. It was found that the turn-on energy delivers the biggest part of the switching losses. The dependence of switching losses from gate resistor is nearly linear, suggesting that changing the gate resistor, a way similar to Si-IGBT technology, can easily control di/dt and dv/dt. Turn-on losses at 200°C are lower compared to those at 25°C, which indicates the influence of the high internal p-type gate layer resistance. Inductive switching numerical analysis suggested the strong influence of channel doping conditions on the turn-on switching performance. The fast switching normally-off JFET devices require heavily doped narrow JFET channel design. © (2009) Trans Tech Publications, Switzerland.

Effect of hydrogen dilution on the deposition of carbon-rich a-SiC:H films by the electron cyclotron resonance method

The deposition of hydrogenated amorphous silicon carbide (a-SiC:H) films from a mixture of silane, acetylene and hydrogen gas using the electron cyclotron resonance chemical vapour deposition (ECR-CVD) process is reported. The variation in the deposition and film characteristics such as the deposition rate, optical band gap and IR absorption as a function of the hydrogen dilution is investigated. The deposition rate increases to a maximum value of about 250 Å min-1 at a hydrogen dilution ratio of about 20 (hydrogen flow (sccm)/acetylene + silane flow (sccm)) and decreases in response to a further increase in the hydrogen dilution. There is no strong dependence of the optical band gap on the hydrogen dilution within the dilution range investigated (10-60) and the optical band gap calculated from the E04 method varied marginally from about 2.85 to 3.17 eV. The room temperature photoluminescence (PL) peak energy and intensity showed a prominent shift to a maximum value of about 2.17 eV corresponding to maximum PL intensity at a moderate hydrogen dilution of about 30. The PL intensity showed a strong dependence on the hydrogen dilution variation.

A microstructural investigation of deformation in fine SiC particulate- and whisker-reinforced aluminium-matrix composites

Aluminium-based composites, reinforced with low volume fractions of whiskers and small particles, have been formed by a powder route. The materials have been tested in tension, and the microstructures examined using transmission electron microscopy. The whisker composites showed an improvement in flow stress over the particulate composites, and this was linked to an initially enhanced work-hardening rate in the whisker composites. The overall dislocation densities were estimated to be somewhat higher in the whisker composites than the particulate composites, but in the early stages of deformation the distribution was rather different, with deformation in the whisker material being far more localized and inhomogeneous. This factor, together with differences in the internal stress distribution in the materials, is used to explain the difference in mechanical properties.