Objective
Silicon carbide (SiC) is currently the only wide band-gap material available in large single crystals which has figures of merit orders of magnitude higher than silicon. Due to its very attractive physical and electronic properties, this semiconductor is a good candidate for high-temperature and high-power device applications. Despite progress in the last decade, important improvements in material and technology development remain to be achieved in order to produce SiC high-voltage power devices.
The purpose of the present programme is to study SiC capability at high voltage, above a few kilovolts, through the simulation and realisation of SiC junction diodes.
On the one hand, the maximum sustainable reverse voltage of a p-n junction is related to breakdown mechanisms in the semiconductor volume, which depends both on its quality and on its critical electrical strength. With a superior critical electric field, high-quality SiC enables higher breakdown voltages to be obtained, with lower thickness and higher doping concentration for the depleted layer, than are achieved by silicon. To obtain junction diode breakdown voltages of a few kilovolts, which is the aim of this work, 6H- or 4H-SiC substrates, with a homoepitaxial layer having a thickness of few tens of mm and a doping concentration level less than 1016 cm{-3}are needed.
On the other hand, the maximum sustainable reverse voltage of a p-n junction is also related to surface breakdown mechanisms occurring at its periphery, which reduce the value of the volume breakdown voltage. It is therefore necessary to think of techniques of periphery protection and surface treatment to prevent such a decrease in breakdown voltage.
The present study includes the improvement of a CVD epitaxial growth set-up in order to produce suitable low-doped SiC layers, and the realisation of high voltage p-n diodes, currently feasible if using bought materials. The latter task involves work on computer-aided design for definition of the diode structure, on the technological steps required for periphery protection, such as plasma etching, passivation, surface treatments, implantation, and on measurement and analysis of the diode reverse current/voltage characteristics for high-voltage breakdown investigation, like analysis of material, doping, thickness, area and defect influences on breakdown voltage.
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69621 Villeurbanne
France