Arrays of dislocation free uniform Ga-polar GaN columns have been realized on patterned SiO x /GaN/sapphire templates by metal organic vapor phase epitaxy using a continuous growth mode. The key parameters and the physical principles of growth of Ga-polar GaN three-dimensional columns are identified, and their potential for manipulating the growth process is discussed. High aspect ratio columns have been achieved using silane during the growth, leading to n-type columns. The vertical growth rate increases with increasing silane flow. In a core–shell columnar LED structure, the shells of InGaN/GaN multi quantum wells and p-GaN have been realized on a core of n-doped GaN column. Cathodoluminescence gives insight into the inner structure of these core–shell LED structures.

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In this work we focus on the impact of different buffer and nucleation layers on the corresponding crystalline quality of gallium nitride (GaN), grown by metal-organic chemical vapour deposition (MOCVD). In situ curvature measurements, X-ray diffraction (XRD) and transmission electron microscopy (TEM) are used for advanced characterization. The influence of various growth modes on meltback etching and cracking is analyzed. Also the effect of a silicon nitride (SiN) mask on the growth of GaN and its coalescence is investigated. Furthermore, associated potential consequences for the growth of aluminium nitride (AlN) interlayers are examined to obtain a homogeneous surface without cracks and with good crystalline quality. Our studies indicate that an incomplete coalesced GaN surface located underneath the AlN interlayer leads to an increased defect density. Additionally we studied the influence of growth temperature at nucleation on the material quality and the process stability. Finally we demonstrate interlayer induced compressive strain during GaN growth with an XRD rockingcurve full width half maximum (FWHM) as low as 450 arc seconds for the 1012 reflection.

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