Coalescence overgrowth of GaN nanocolumns on sapphire with patterned metal organic vapor phase epitaxy

Abstract

High-quality coalescence overgrowth of patterned-grown GaN nanocolumns on c-plane sapphire substrate with metal organic chemical vapor deposition is demonstrated. Although domain structures of a tens of micron scale in the overgrown layer can be identified with cathodoluminescence measurement, from atomic force microscopy ͑AFM͒ measurement, the surface roughness of the overgrown layer in an area of 5 ϫ 5 m 2 is as small as 0.411 nm, which is only one-half that of the high-quality GaN thin-film template directly grown on sapphire substrate ͑the control sample͒. Based on the AFM and depth-dependent x-ray diffraction measurements near the surface of the overgrown layer, the dislocation density is reduced to the order of 10 7 cm −2 , which is one order of magnitude lower than that of the control sample and two to three orders of magnitude lower than those of ordinary GaN templates for fabricating light-emitting diodes. Also, the lateral domain size, reaching a level of ϳ2.7 m, becomes three times larger than the control sample. Meanwhile, the ratio of photoluminescence intensity at room temperature over that at low temperature of the overgrown sample is at least six times higher than that of the control sample. Although the strain in nanocolumns is almost completely released, a stress of ϳ0.66 GPa is rebuilt when the coalescence overgrowth is implemented.

Threading dislocation evolution in patterned GaN nanocolumn growth and coalescence overgrowth

“…The detailed fabrication and growth conditions have been discussed in a recent publication of the same group. 23 All the samples were examined with PL spectroscopy, SEM, and cross-sectional TEM. The overgrowth samples and GaN template were also characterized with AFM and depthdependent XRD measurements.…”

“…The detailed description of this technique has been presented in the earlier publication. 23 The TEM investigations were performed using a Philips Tecnai F30 field emission electron microscope with an accelerating voltage of 300 kV and a probe forming lens of Cs= 1.2 mm. The SEM measurement was performed with a JEOL JSM 6700F system.…”

“…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.…”

“…Improved GaN quality in an overgrown layer based on MOCVD coalescence overgrowth of such NCs has also been reported. 23 In this paper, the TD evolution behaviors during patterned NC growth and coalescence overgrowth with MOCVD are studied based on the comparisons of NC and coalescence overgrowth samples of different NC cross section and spacing sizes. From the measurement results of depth-dependent x-ray diffraction ͑XRD͒ and cross-section transmission electron microscopy ͑TEM͒, it is found that whether a TD can penetrate into an NC depends on the patterned hole size for NC growth.…”

Analysis of threading dislocations in void shape controlled GaN re-grown on hexagonally patterned mask-less GaN

“…In recent years, there has been an increased interest towards the selective area growth of GaN through highly defined pore openings on GaN templates [17]. Results have shown that the dislocations can be effectively filtered by columnar growth through the pores.…”