Gradual tilting of crystallographic orientation and configuration of dislocations in GaN selectively grown by vapour phase epitaxy methods

Cross-sectional transmission electron microscope (TEM) observation was perf ormed for selectively grown gallium nitride (GaN) in order to examine the d ependence of GaN microstructure on the growth conditions. The GaN films wer e grown by hydride vapour phase epitaxy (HVPE) or metalorganic vapour phase epitaxy (MOVPE) on GaN covered with a patterned mask. Thin foil specimens for TEM observation were prepared with focused ion beam (FIB) machining app aratus. It was demonstrated that the c-axis of GaN grown over the terrace o f the mask tilts towards the centre of the terrace when the GaN is grown in a carrier gas of N-2. The wider terrace results in a larger tilting angle if other growth conditions are identical. The tilting is attributed to 'hor izontal dislocations' (HDs) generated during the overgrowth of GaN on the m ask terrace. The HDs in HVPE-GaN have a semi-loop shape and are tangled wit h one another, while those in MOVPE-GaN are straight and lined up to form l ow-angle grain boundaries.