Papers by Author: Christian Strenger

Abstract: N-LDMOS and n-LIGBT structures were manufactured with the same dimensions on a 4H-SiC wafer in order to allow for a direct comparison. The comparison of the devices includes output and transfer characteristics, blocking characteristics, and temperature behavior.

Abstract: To study mobility limiting mechanisms in (0001) 4H-SiC, lateral n-channel MOSFETs in p-implanted wells on n-type epitaxial layers were manufactured and additionally selectively shallow implanted with different nitrogen (N) doses in the channel region. The mobility was found to be limited by Columbic scattering at low electric fields. Further surface roughness scattering was con-sidered as a possible mobility degradation mechanism at high electric fields. First investigations of the SiC surface by atomic force microscopy (AFM) in the channel region after implantation, anneal-ing, and gate oxide removal revealed a rather rough topology. This could lead to fluctuations in the surface potential at the SiC/SiO2 interface, thus accounting in part for surface roughness scattering.

Abstract: 4H-SiC n-channel lateral MOSFETs were manufactured and characterized electrically by current-voltage measurements and by numerical simulation. To describe the observed electrical characteristics of the SiC MOSFETs, Near-Interface Traps (NIT) and mobility degradation models were included in the simulation. The main finding of the simulation is that two models for the NIT states in the upper part of the SiC bandgap are able to describe the electrical data equally well. In one of them, acceptor-like traps and fixed charge are considered while in a newly developed one, donor-like traps are taken into account also.

Abstract: Effect of a shallow nitrogen implantation in the channel region of n-channel 4H-SiC Hall bar MOSFETs on their electrical properties has been characterized by Hall effect. A significant improvement of Hall mobility in normally-off devices is observed with increasing nitrogen implantation dose up to 10¹³ cm^-2 with a peak Hall mobility of 42.4 cm².V^-1.s^-1. Coulomb scattering as dominant scattering mechanism up to room temperature is demonstrated using temperature dependent MOS-Hall effect characterization.

Abstract: N-channel MOSFETs were manufactured on p-type and on p-implanted, n-type 4H-SiC substrates. The electron mobility in the inversion channel was measured to be correlated with the structural and chemical properties determined by transmission electron microscopy. With regard to what was previously discussed in the literature, interfacial layer formation and carbon distribution across the SiC/SiO2 interface were considered in relation with the measured Hall electron mobility.

Abstract: 4H-SiC presents great advantages for its use in power electronic devices working at particular conditions. However the development of MOSFETs based on this material is limited by mobility degradation. N-channel SiC MOSFETs were manufactured on p-type epitaxial and p-implanted substrates and the electron mobility in the inversion channels was measured to be correlated with their structural and chemical properties determined by transmission electron microscopy methods. With regard to what was previously discussed in the literature, transition layer formation and carbon distribution across the SiC-SiO₂ interface are considered in relation with the measured low electron mobility of the MOSFETS.

Abstract: Metal-oxide-semiconductor (MOS) capacitors were formed on 4H-silicon carbide (SiC) using thermally grown silicon dioxide (SiO2) as gate dielectrics, both with and without nitrogen incorporation within the oxide. The field dependence of the charge trapping properties of these structures was analyzed and linked to the observed Fowler-Nordheim current degradation. Furthermore, first considerations were presented that indicate an electron impact emission induced generation of positive oxide trapped charge.