ATTENTION !!! SEMINAIRE ANNULE !!! Synthesis and characterization of new Al-Si-C system semiconductor

Orateur : Hoang Long LE TRAN (PhD Student - LMGP - UGA)

Al4SiC4 is a refractory ceramic with a reported band gap of about 2.5 eV, making it an interesting semiconductor material for various applications in the field of energy. However, the synthesis of Al4SiC4 single crystals has so far not been investigated. In the first part of this thesis, combining a thermodynamic analysis with a focused experimental approach, the vaporization and condensation phenomena in the Al4C3-SiC system are described. Experimental conditions, such as initial composition, baking temperature and temperature gradient, are investigated and optimized regarding the crystallization of Al4SiC4. From the results obtained, a condensed phase diagram at equilibrium is established for the molar fraction XAl4C3/(Al4C3+SiC) < 0.5, which is determined as the favorite condition for the Al4SiC4 condensation. Indeed, Al4SiC4 single phase could be experimentally synthesized by sublimation at 1900°C with a temperature gradient smaller than 40°C. Some basics characteristics of obtained Al4SiC4 crystalline layers like the structural quality and optical absorption are investigated. In the second part, new hetero-epitaxial structures on [0001] oriented hexagonal SiC are studied like Al4C3/SiC and Al4SiC4/SiC. The characteristics of heterostructures, like growth mechanism and crystallographic relationships are mainly investigated in nanoscopic scale by using high resolution TEM. 

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