Analysis of the extended defects in 3C-SiC.pdf - Nelson Mandela ...
Analysis of the extended defects in 3C-SiC.pdf - Nelson Mandela ...
Analysis of the extended defects in 3C-SiC.pdf - Nelson Mandela ...
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SUMMARY<br />
The dissertation focuses on <strong>the</strong> analysis <strong>of</strong> <strong>the</strong> <strong>extended</strong> <strong>defects</strong> present <strong>in</strong> as-grown<br />
and proton bombarded β-<strong>SiC</strong> (annealed and unannealed) grown by chemical vapour<br />
deposition (CVD) on (001) Si. The proton irradiation was done to a dose <strong>of</strong> 2.8 × 10 16<br />
protons/cm 2 and <strong>the</strong> anneal<strong>in</strong>g took place at 1300°C and 1600°C for 1hr. The ma<strong>in</strong><br />
techniques used for <strong>the</strong> analysis were transmission electron microscopy (TEM) and<br />
high resolution TEM (HRTEM).<br />
From <strong>the</strong> diffraction study <strong>of</strong> <strong>the</strong> material <strong>the</strong> phase <strong>of</strong> <strong>the</strong> <strong>SiC</strong> was confirmed to be<br />
<strong>the</strong> cubic beta phase with <strong>the</strong> z<strong>in</strong>c-blende structure. The ma<strong>in</strong> <strong>defects</strong> found <strong>in</strong> <strong>the</strong> β-<br />
<strong>SiC</strong> were stack<strong>in</strong>g faults (SFs) with <strong>the</strong>ir associated partial dislocations and<br />
microtw<strong>in</strong>s. The SFs were uniformly distributed throughout <strong>the</strong> foil. The SFs were<br />
identified as hav<strong>in</strong>g a fault vector <strong>of</strong> <strong>the</strong> type 1/3 with bond<strong>in</strong>g partial<br />
dislocations <strong>of</strong> <strong>the</strong> type 1/6 by us<strong>in</strong>g image simulation. The SFs were also<br />
found to be predom<strong>in</strong>antly extr<strong>in</strong>sic <strong>in</strong> nature by us<strong>in</strong>g HRTEM analysis <strong>of</strong> SFs<br />
viewed edge-on. Also both bright and dar-field images <strong>of</strong> SFs on <strong>in</strong>cl<strong>in</strong>ed planes<br />
exhibited symmetrical and complementary fr<strong>in</strong>ge contrast images. This is a result <strong>of</strong><br />
<strong>the</strong> anomalous absorption ratio <strong>of</strong> <strong>SiC</strong> ly<strong>in</strong>g between that <strong>of</strong> Si and diamond.<br />
The analysis <strong>of</strong> <strong>the</strong> annealed and unannealed irradiated β-<strong>SiC</strong> yielded no evidence <strong>of</strong><br />
radiation damage or change <strong>in</strong> <strong>the</strong> crystal structure <strong>of</strong> <strong>the</strong> β-<strong>SiC</strong>. This confirmed that<br />
β-<strong>SiC</strong> is a radiation resistant material. The critical proton dose for <strong>the</strong> creation <strong>of</strong><br />
small dislocation loops seems to be higher than for o<strong>the</strong>r compound semiconductors<br />
with <strong>the</strong> z<strong>in</strong>c-blende structure.