Papers by Author: Teddy Robert

Abstract: Both 3C and 6H stacking faults have been observed in a low doped 4H-SiC epitaxial layer grown in a hot-wall CVD reactor on a heavily doped (off-axis) 4H-SiC substrate. They appear differently on the different parts of sample, with energetic dispersion ranging from 3.01 eV to 2.52 eV. Since they behave as natural type-II quantum wells in the 4H-SiC matrix, the thickness dependence of the excitonic recombination is investigated using the standard effective mass approximation. The results are discussed in terms of built-in electric field and inter-well coupling effects.

Abstract: In the present work the defects appearing in layers grown by liquid phase epitaxy on different substrates are compared. The used seeds were (i) 3C-SiC with (111) orientation, grown heteroepitaxially on (0001) 4H-SiC or 6H-SiC substrates by continuous feed physical vapour transport process and the vapour-liquid-solid mechanism, respectively, and (ii) 3C-SiC wafer with (100) orientation from HOYA. The structural and optical investigation showed that (i) on the (111) substrates, due to the appearance of silicon and 6H-SiC inclusions, a layer which consisted of a sequence of long period polytypes was formed. The dominant polytype formed was 21R-SiC, which after successive transformation to 39R- and 57R- SiC led to the formation of 6H-SiC on the top of the layer. (ii) On the (100) substrates, a 3C-SiC layer with comparatively uniform defect density was formed. The main defects were stacking faults and their density was reducing during the process.

Abstract: A new type of 6H zigzag faults has been identified from high resolution transmission electron microscopy (HRTEM) measurements performed on low-doped 4H-SiC homoepitaxial layer grown on off-axis substrates in a hot-wall CVD reactor. They are made of half unit cells of 6H with corresponding low temperature photoluminescence (LTPL) response ranging from about 3 eV to 2.5 eV at liquid helium temperature.

Abstract: The electronic structure of in-grown 8H stacking faults in 4H-SiC matrix has been investigated in detail. After assessment of the structural properties by high resolution transmission electron microscopy, we focus on the electronic structure. We show that one unit cell of 8H does not behave like a single type-II quantum well but, rather, like two type-II quantum wells of 3C coupled by a thin hexagonal barrier. Using a transfer matrix method, we compute the corresponding transition energies, taking into account the effect of the valence band offset and built-in electric field. A good agreement is found with the experimental data collected from low temperature photoluminescence spectroscopy.

Abstract: We present a structural and optical investigation of nitrogen-doped single crystals of cubic silicon carbide prepared by the continuous feed - physical vapour transport method. Self-nucleated crystals were produced which exhibited well faceted square and triangular shapes. KOH etching was used to characterize the structural defects, like stacking faults and dislocations. The effect of changing the nitrogen flow rate on the different crystalline orientations was investigated by Raman spectroscopy and low temperature photoluminescence techniques.