Dual-polarity GaN micropillars grown by metalorganic vapour phase epitaxy: Cross-correlation between structural and optical properties

This study investigates self-assembled, catalyst-free GaN micropillars (μpillars) grown on (0001) sapphire substrates by metalorganic vapour phase epitaxy (MOVPE). Transmission electron microscopy (TEM) and KOH chemical etching reveal the systematic coexistence of two domains of opposite polarity (Ga-polar and N-polar) within each single micropillar, originating at the micropillar/substrate interface during nucleation and propagating along the entire length of the pillar. Dislocations are generated at the wire/substrate interface but bend after several hundreds of nanometers, resulting in dislocation-free micropillars of several tens of micrometers in length. Spatially resolved cathodoluminescence (CL) and microphotoluminescence (μPL) reveal large optical property differences between the two polarity domains, attributed to unequal incorporation of impurities, dopants and vacancies depending on polarity.

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