Improved SiC Epitaxial Material for Bipolar Applications
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Improved SiC Epitaxial Material for Bipolar Applications Peder Bergman1,2, Jawad ul Hassan1, Alex Ellison2, Anne Henry1, Philippe Godignon3, Pierre Brosselard3, and Erik Janzén1 1 Department of Physics, Chemistry and Biology, Linköping University, IFM, Linköping, SE-581 83, Sweden 2 Norstel AB, Ramshällsvägen, Norköping, S-60116, Sweden 3 CNM-IMB-CSIC, Campus UAB, Bellaterra, Barcelona, ES-08193, Spain ABSTRACT Epitaxial growth on Si-face nominally on-axis 4H-SiC substrates has been performed using horizontal Hot-wall chemical vapor deposition system. The formation of 3C inclusions is one of the main problem with growth on on-axis Si-face substrates. In situ surface preparation, starting growth parameters and growth temperature are found to play a vital role in the epilayer polytype stability. High quality epilayers with 100% 4H-SiC were obtained on full 2” substrates. Different optical and structural techniques were used to characterize the material and to understand the growth mechanisms. It was found that the replication of the basal plane dislocation from the substrate into the epilayer can be eliminated through growth on on-axis substrates. Also, no other kind of structural defects were found in the grown epilayers. These layers have also been processed for simple PiN structures to observe any bipolar degradation. More than 70% of the diodes showed no forward voltage drift during 30 min operation at 100 A/cm2. INTRODUCTION The superior physical properties of SiC, like wide band gap, high thermal conductivity and high breakdown electric field, make it potentially useful semiconductor material for high power, high temperature and high frequency electronics devices. SiC exists in many different polytypes and the difference between polytypes lies in the stacking sequence of Si-C bilayers along the caxis. In order to replicate the substrate polytype into the epilayer, off-axis substrate with several degree off-cut typically along [ 1120 ] direction is used. The steps produced on the off-axis surface reveal the substrate polytype and act as a continuous source of polytype information of the crystal during epitaxial growth [1]. However, the major problem with the growth on off-cut substrate is the replication of the basal plane dislocations (BPDs) from the substrate into the epilayer. In the case of high power bipolar electronic devices the BPDs are reported to act as a source of the formation of the stacking faults on the basal plane during bipolar injection. These stacking faults result in an increased forward voltage drop and is known as bipolar degradation [2,3]. Bipolar degradation has in recent years been extensively studied. The increase in the forward voltage drop in bipolar PiN diodes due to the expansion and propagation of the stacking faults along the basal-plane throughout the active area has been well understood. Different techniques have also been proposed to reduce the number of basal-plane dislocations that are the main source of the stacking faults [4,5]. These techniques increase the con
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