Papers by Author: Peter Friedrichs

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Authors: Birgit Kallinger, Patrick Berwian, Jochen Friedrich, Mathias Rommel, Maral Azizi, Christian Hecht, Peter Friedrichs
Abstract: 4H-SiC homoepitaxial layers with different thicknesses from 12.5 µm up to 50 µm were investigated by microwave-detected photoconductivity decay (µ-PCD), deep level transient spectroscopy (DLTS) and defect selective etching (DSE) to shed light on the influence of the epilayer thickness and structural defects on the effective minority carrier lifetime. It is shown that the effective lifetime, resulting directly from the µ-PCD measurement, is significantly influenced by the surface recombination lifetime. Therefore, an adequate correction of the measured data is necessary to determine the bulk lifetime. The bulk lifetime of these epilayers is in the order of several microseconds. Furthermore, areas with high dislocation density are correlated to areas with locally reduced effective lifetime.
Authors: Peter Friedrichs, Reinhold Bayerer
Abstract: Silicon carbide power devices are intended and to enter new application regimes in power electronics, in fact, they are enabling components mainly if higher switching frequencies in power electronics are considered. This trend can be clearly observed since power density can be increased and efforts towards passive components and other mechanical contributions to the system can be reduced. However, this trend imposes new challenges towards the surrounding of the chips in form of the package itself and the whole system around. Stray components like inductances and impedance elements become crucial elements in the whole circuit what results in the fact that a simple exchange of silicon chips by silicon carbide in a given package can be ruled out. In addition different considerations regarding the thermal design especially in power modules arise when SiC chips are considered, triggered by the fact that the cost balance between assembly and chip is shifted compared to silicon based solutions. Thus, different optimization criteria can be used, leading to new design approaches for power modules. The following paper will give a first inside how those boundary conditions can be implemented in innovative solutions using SiC components.
Authors: Birgit Kallinger, Patrick Berwian, Jochen Friedrich, Christian Hecht, Dethard Peters, Peter Friedrichs, Bernd Thomas
Abstract: 4H-SiC PiN diodes for 6.5 kV were manufactured on both 4° and 8° off-cut substrates and subjected to an electrical stress test on wafer level and subsequent analysis of structural defects present in the active area of the diodes. For 8° off-cut diodes, the electrical characteristics with respect to leakage current and forward voltage drift are worse than the electrical characteristics of 4° off-cut diodes. Furthermore, a large number of stacking faults was found in 8° off-cut diodes, but little evidence for bipolar degradation was found in 4° off-cut diodes. Therefore, bipolar degradation was significantly reduced by avoiding BPDs in the active area of PiN diodes, i.e. by the use of 4° off-cut substrates. Furthermore, a strong correlation was found between the electrical screening test on wafer level and critical defects.
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