Study by Weak Beam and HRTEM of double stacking faults created by external mechanical stress in 4H-SiC
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Study by Weak Beam and HRTEM of double stacking faults created by external mechanical stress in 4H-SiC Hosni Idrissi, Maryse Lancin, 1Joel Douin, Gabrielle Regula, Bernard Pichaud, Rachid El Bouayadi, Jean-Marc Roussel TECSEN, UMR-6122, Université Aix-Marseille III, 13397 Marseille-cedex20 -France 1 LEM, CNRS-ONERA, BP 72, 92332, Chatillon-cedex-France ABSTRACT 4H-SiC samples are bent in compression mode at 550°C and 620°C. The introduced-defects are identified by Weak Beam and HRTEM techniques. They consist of double stacking faults bounded by 30° Si(g) partial dislocations whose glide locally transforms the material in its cubic phase. The velocity of partial dislocations is measured after chemical etching of the sample surface. The formation and the expansion of the double stacking faults are discussed. INTRODUCTION Silicon carbide is a wide band gap semiconductor that holds promise as a material for power electronics, high frequency and high temperature applications. Though its crystalline quality has been significantly improved this last decade, many authors reported the formation of defects which are device killers. All these defects involve the formation of either single stacking faults (SFs) or double stacking faults (DSFS) bounded by Shockley partials and creating locally either single layer or double-stacked layers of 3C-SiC in the 4H-SiC matrix. These 3C-SiC layers are observed in samples containing a high amount of injected-charge carriers [1-6]. They can be found as well in highly n doped (1.7×1019cm-3) epilayers deposited on lightly doped substrates during a thermal oxidation step [7] or high temperature annealing (1150°C) [8,9]. Because of the detrimental electrical impact of these defects on the device properties, number of studies are being performed to determine their structure and to understand their nucleation and propagation mechanisms. The SFS (or DSFs) expansion described in the literature is ascribed to different phenomena: i) the internal stress resulting from the lattice mismatch due to the doping difference between the epilayer and the substrate [8,10] ii) the lowering of the energy of highly n doped-crystal through electrons entering Quantum-Well-Like states associated with DSFs [8,9,11]. The aim of this work is to introduce DSFs by external mechanical stress and to measure directly the velocity of partials bounding them. We describe the deformation procedure, we identify the DSFs and the created-partials using Weak Beam (WB) and HRTEM techniques. We determine the velocity of the partials and propose a frame to explain both their nucleation and the DSFs expansion. EXPERIMENTS We use 4H-SiC nitrogen-doped (5×1018cm-3) wafers provided by Cree-Research. The (1120) orientation of the wafers and the sample geometry are selected to introduce a controlled population of dislocations. The {0001} glide planes are perpendicular to the sample surface and
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at 45° from the tension-compression axis (X). The latter is 1.7° disoriented from the 2 201 direction (Fig.1a). Only t
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