Microstructural Aspects and Mechanism of Degradation of 4H-SiC PiN Diodes under Forward Biasing
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Microstructural Aspects and Mechanism of Degradation of 4H-SiC PiN Diodes under Forward Biasing 1
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Pirouz Pirouz , Ming Zhang , Augustinas Galeckas , and Jan Linnros 1 Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106-7204, U.S.A. ([email protected]) 2 Department of Microelectronics and Information Technology, Royal Institute of Technology (KTH), SE 16440 Stockholm-Kista, Sweden ABSTRACT Devices fabricated from the wide bandgap semiconductor SiC have many advantages over those made from conventional semiconductors. Thus, performance characteristics of some 4H-SiC devices can be two orders of magnitude better than equivalent devices made from silicon. On the other hand, new and unexpected problems have emerged with the operation of some SiC devices that need to be understood and solved before further progress can be made in this area. One of the most intriguing problems has been the degradation of bipolar PiN diodes that have major advantages over unipolar Schottky barrier diodes at high blocking voltages. The electrical degradation of the PiN diodes refers to a drop in voltage under extended forward current operation. The degradation appears to be associated with the appearance of stacking faults (SFs) in the entire base region of the diode. In this paper, we discuss some puzzling aspects of stacking fault formation in such diodes. Electroluminescence as well as TEM has been used to investigate the degradation problem and, based on experimental results, the formation of stacking faults within the device, possible sources of partial dislocations responsible for the stacking faults, and the enhanced motion of dislocations under forward biasing are considered. INTRODUCTION As a tetrahedrally-coordinated semiconductor, silicon carbide (SiC) has always been an attractive material for the fabrication of electronic devices. In fact, William Shockley himself, recognized the unique potential of SiC early on [1]. These advantages mostly arise from the fundamental material properties of SiC, properties such as the wide band gap - from 2.4 (3CSiC) to 3.4 eV (2H-SiC) - compared to 1.1 eV for silicon - and the excellent high temperature mechanical properties of this material. The wide band gap means that doped SiC can keep its extrinsic conductivity up to much higher temperatures (as compared to conventional semiconductors) and that its critical field for avalanche breakdown is very high (about ten times larger than that for silicon). Similarly, the better mechanical properties of SiC indicate that nucleation and glide of line defects (dislocations) in the material is much more difficult than in smaller bandgap semiconductors. Since SiC wafers became commercially available in the beginning of the nineties, the pace of research on the electronic applications of SiC has accelerated worldwide and there have been a number of prototype electronic devices fabricated on the material. The experimental results basically confirm the unique advantageous properties of SiC and t
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