Overgrowth and strain investigation of (11–20) non-polar GaN on patterned templates on sapphire

Abstract

Non-polar (11–20) GaN with significantly improved crystal quality has been achieved by means of overgrowth on regularly arrayed micro-rod templates on sapphire in comparison with standard non-polar GaN grown without any patterning processes on sapphire. Our overgrown GaN shows massively reduced linewidth of X-ray rocking curves with typical values of 270 arcsec along the [0001] direction and 380 arcsec along the [1–100] direction, which are among the best reports. Detailed X-ray measurements have been performed in order to investigate strain relaxation and in-plane strain distribution. The study has been compared with the standard non-polar GaN grown without any patterning processes and an extra non-polar GaN sample overgrown on a standard stripe-patterned template. The standard non-polar GaN grown without involving any patterning processes typically exhibits highly anisotropic in-plane strain distribution, while the overgrown GaN on our regularly arrayed micro-rod templates shows a highly isotropic in-plane strain distribution. Between them is the overgrown non-polar GaN on the stripe-patterned template. The results presented demonstrate the major advantages of using our regularly arrayed micro-rod templates for the overgrowth of non-polar GaN, leading to both high crystal quality and isotropic in-plane strain distribution, which is important for the further growth of any device structures.

Monolithic multiple colour emission from InGaN grown on patterned non-polar GaN

“…For details, please refer to ref. 23 . The dislocation density of our non-polar GaN overgrown on micro-rod arrayed templates has been substantially reduced down to 6 × 10 8 /cm 2 from a typical dislocation density of 10 11 /cm 2 for non-polar GaN directly grown on sapphire without involving overgrowth.…”

“…The non-polar GaN is then fabricated into regular micro-rod arrays with a SiO 2 mask on top of each micro-rod. The details of the fabrication procedure can be found elsewhere 23 .…”

“…This not only effectively reduces defects but also helps to form semi-polar facets. Such a regularly arrayed micro-rod template was originally designed for overgrowth of (11–20) non-polar GaN with a step-change in crystal quality 23 .…”

Optical and polarization properties of nonpolar InGaN-based light-emitting diodes grown on micro-rod templates

“…Moreover, epitaxial lateral overgrowth approaches have been also extended to the nonpolar GaN growth on planar sapphire 16–18 , nomally employing stripe-patterned templates. However, it is usually difficult to achieve an atomically flat surface on such a stripe-patterned template due to the intrinsically anisotropic in-plane growth rate 19 . Using an array of hexagonal SiO 2 patterns, high quality a -plane GaN have been achieved on sapphire substrates.…”

“…Our group has achieved high quality nonpolar (11–20) GaN films by using an overgrowth approach on regularly arrayed (11–20) GaN micro-rods on r-plane sapphire 19 . The X-ray rocking curves demonstrate the line widths are 270 arcsec along the c -direction and 380 arcsec along the m - direction, which is the best report so far.…”