Papers by Author: Etienne Pernot

Abstract: The dislocation-induced birefringence of Silicon Carbide (SiC) is analytically and quantitatively modelled by using the adequate SiC data. A good agreement can be obtained between theory and experiment, provided that a background residual (uniaxial) stress is added to the local dislocation-induced stress. Observations are compatible with or predictable from the Burgers vector values, so that birefringence reveals an interesting tool for probing the nature of the dislocations associated, e.g., to micropipes, also faster than and complementary to the more involved transmission electron microscopy (TEM) technique.

Abstract: AlN is considered as the most suitable substrate material for further development of high quality and high performance nitride-based micro- and opto-electronics. AlN ingots are often grown on SiC seeds. To solve the formation of cracks due to the difference in lattice parameters between seed and crystal we chose to “adapt” the lattice mismatch by a buffer layer of the (AlN)x(SiC)1-x solid solution. This paper gives some inputs on the growth of AlN and the solid solution by the sublimation technique, in terms of materials compatibility, hetero- and homo-epitaxial growth of AlN and on the preparation of crack-free solid solution single crystals.

Abstract: Recently, in some silicon carbide single crystals, some micropipes associated with screw dislocation have been observed by X-ray topography and the strain field around them produced images similar to those of screw dislocations with a very large Burgers vector, about 667 nm. The radius of the hole in the centre of the micropipe is less than 10 'm. This value and the theoretical predictions by Frank (about 7.8 mm) using the Burgers vector magnitude show a large discrepancy. In this paper we present Atomic Force Microscopy experiments around this kind of defects. The Burgers vector magnitude of the screw dislocation and the value of the radius have been measured by this technique. Not only one dislocation, but several have been observed around the micropipe. We concluded that it is in better agreement with the Frank theory modified by Cabrera and Levine concerning kinetic effects during the growth.

Abstract: Because of the formation of DPB (Double Positioning Boundary) when starting from a hexagonal <0001> seed, DPB-free 3C-SiC single crystals have never been reported up to now. In a recent work we showed that, using adapted nucleation conditions, one could grow thick 3C-SiC single crystal almost free of DPB [1]. In this work we present the results of a multi-scale investigation of such crystals. Using birefringence microscopy, EBSD and HR-TEM, we find evidence of a continuous improvement of the crystal quality with increasing thickness in the most defected area, at the sample periphery. On the contrary, in the large DPB-free area, the SF density remains rather constant from the interface to the surface. The LTPL spectra collected at 5K on the upper part of samples present a nice resolution of multiple bound exciton features (up to m=5) which clearly shows the high (electronic) quality of our 3C-SiC material.

Abstract: The transfer by wafer-bonding of single-crystalline SiC thin films to a polycrystalline SiC support to obtain a “quasi-wafer” is an attractive way for lowering the cost of silicon carbide wafers. Such a process needs high quality polycrystalline substrates, with controlled and high-level bulk properties (thermal conductivity, electrical resistivity) and with very low surface roughness and surface bowing. Currently, polycrystalline SiC wafers which are available are siliconized SiC or CVD processed SiC wafers. Siliconized ceramic wafers are very heterogeneous (mixture of 3C, 6H, 15R and silicon), while CVD ones are of better quality (homogeneous and textured 3C). However neither the siliconized SiC nor the CVD SiC can be CMP polished with low roughness over large dimension. In this paper, wafers with large and textured grains (> 1cm) are processed and characterized. The polishing of such structures is studied and optimized to obtain low surface roughness. To meet these requirements high temperature processes used for single crystal growth were selected. Structural investigations performed on the grown ingots showed an important influence of the used seed since no preferential crystallographic orientation was observed during the growth. The final polishing quality was of high level but step heights were observed between grains.

Abstract: Structural defects in SiC crystals were investigated and 4H-SiC pin devices were characterized by micro-Raman scattering and photoemission. With the experimental set-up presented, defects could be successfully detected in SiC crystals but stacking faults could not be detected with micro-Raman scattering, although they could be detected by photoemission. Residual stress could be evaluated in 4H-SiC devices, as well as the temperature increase associated with the devices powering. A good correlation was found between the characterization techniques used: micro-Raman scattering and photoemission.