Coalescence overgrowth of GaN nano-columns with metalorganic chemical vapor deposition

Abstract

The authors demonstrate the coalescence overgrowth of GaN nano-columns on a (111) Si substrate with metalorganic chemical vapor deposition to show high-quality optical properties in the overgrown film. Plan-view scanning electron microscopy (SEM) shows coalesced surface morphology, although hexagonal structures are still visible in the images. The cross-section cathodoluminescence (CL) image shows more efficient emission in the overgrowth layer than from the nano-column layer. The plan-view CL image demonstrates that the emitted light is mainly from the hexagonal structures. The photoluminescence measurement result indicates that the emission efficiency of the overgrown layer is even higher than that of an undoped GaN thin film of high quality. The presence of hexagonal structures correlates to surface roughness values in the range of several nanometres.

Characterizing the thickness dependence of epitaxial GaN grown over GaN nanocolumns using X-ray diffraction

“…The small FWHM near the surface of sample C2, which is even smaller than that of sample GaN1, implies that the crystal quality of a thin surface layer (around 200 nm in thickness) of the overgrown sample C2 is better than that of the good-quality GaN thin-film control sample. We have also performed photoluminescence measurement (shallow excitation) to show that the integrated luminescence intensity of this sample is seven times stronger than that of the good-quality GaN thinfilm sample [6]. Hence, the overgrowth on GaN NCs at 1000 1C for a thickness over 2 mm can lead to a high-quality GaN template for fabricating optoelectronic or electronic devices.…”

“…However, the fabrication of optoelectronic or photonic devices directly into or on a NC structure is difficult and insufficient for many applications. Therefore, GaN with comparatively small dislocation densities formed by the overgrowth of GaN NCs has been explored as an alternative technique for preparing large-area GaN templates suitable for device fabrication [5,6].…”

Threading dislocation evolution in patterned GaN nanocolumn growth and coalescence overgrowth

“…However, it was found that to achieve high-quality coalescence overgrowth, a regular arrangement of vertical and parallel NCs is preferred. 22,23 Recently, the implementations of such NCs based on patterned metal-organic chemical vapor deposition ͑MOCVD͒ by using interferometry lithography 24 and nanoimprint lithography 23 have been demonstrated. Improved GaN quality in an overgrown layer based on MOCVD coalescence overgrowth of such NCs has also been reported.…”

Controlled Nucleation of GaN Nanowires Grown with Molecular Beam Epitaxy

“…Coalesced GaN nanowires have been used as a template for high-quality GaN epilayer growth. [ 11 ] The PL intensity for nanowires larger than 750 nm between the mask and the surface exposed in patterning of the mask. Typical results for selective epitaxy for SiN x deposited on top of a thin layer of AlN are shown in Figure 1 .…”