Threading dislocation evolution during patterned GaN nanocolumn growth and

coalescence overgrowth with metal-organic chemical vapour deposition was

studied based on the comparisons of nanocolumn and coalescence overgrowth

samples of different nanocolumn cross-section diameters and spacing sizes. From

the measurement results of depth-dependent X-ray diffraction and cross-section

transmission electron microscopy, it was found that the threading dislocation

density in an nanocolumn depends on the patterned hole size for nanocolumn

growth. Also, the threading dislocation formation at the beginning of coalescence

overgrowth was related to the nanocolumn spacing size. Although the threading

dislocation density at the bottom of the overgrown layer was weakly dependent on

nanocolumn and spacing sizes, at its top surface, the threading dislocation density

strongly relies on nanocolumn size. Among the overgrowth samples of different

nanocolumn diameters and spacing sizes with a fixed nanocolumn

diameter/spacing ratio, the one with the smallest size and spacing leads to the

lowest threading dislocation density, the largest lateral domain size, and the highest

photoluminescence efficiency. Also, the optical and crystal qualities at the surfaces

of all the overgrowth samples were superior to those of a GaN template.

Threading Dislocation Evolution in Patterned GaN Nanocolumn Growth and

Coalescence Overgrowth. Y.S.Chen, W.Y.Shiao, T.Y.Tang, W.M.Chang,

C.H.Liao, C.H.Lin, K.C.Shen, C.C.Yang, M.C.Hsu, J.H.Yeh, T.C.Hsu: Journal of

Applied Physics, 2009, 106[2], 023521