Improved semipolar (112¯2) GaN quality using asymmetric lateral epitaxy

Abstract

Semipolar (112¯2) GaN films were obtained by epitaxial lateral overgrowth from (112¯2) GaN templates patterned with SiO2 stripes 7 μm wide with 3 μm spacing, oriented along the [11¯00] GaN in-plane direction. The growth conditions were optimized in order to promote a fast growth rate along the +c [0001] direction. The crystal expands both laterally and vertically until a situation where it overgrows the adjacent crystal, thus stopping the propagation of stacking faults and threading dislocations. The growth anisotropy and filtering of defects is observed by cross-sectional scanning electron microscopy and cathodoluminescence. The lowering of defect density is confirmed by x-ray diffraction measurements. The photoluminescence spectrum of the coalesced epitaxial lateral overgrowth of the (112¯2) epilayers exhibits a strong band edge emission and a low emission band at 3.41 eV, assigned to the remaining stacking faults.

Defect reduction in overgrown semi-polar (11-22) GaN on a regularly arrayed micro-rod array template

“…The overgrowth initiates from the exposed sidewalls of micro-rods as shown in Figure 1(b), and the lateral growth is dominated by the growth along the [0001] direction labelled as c-direction and the [11][12][13][14][15][16][17][18][19][20] direction labelled as a-direction. Comparing the lengths of the two growing wings, the c-direction growth is faster than the a-direction growth.…”

“…On such high quality semi-polar GaN templates, we have achieved high performance semi-polar light emitting diodes (LEDs) with a wide spectral range of up to amber. 16,17 In this letter, we investigate in detail a mechanism of the defect reduction in the overgrown semi-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN on the regular micro-rod array templates by transmission electron microscopy (TEM) measurements, and a detailed model has been established, essentially allowing us to further improve the crystalline quality of overgrowth semi-polar GaN on sapphire.…”

“…A single (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN layer with a thickness of 1.3 µm is grown on m-plane sapphire using our high temperature AlN buffer by metal organic chemical vapor deposition (MOCVD). 18 For subsequent overgrowth, mask-patterned micro-rod arrays have been fabricated on the semi-polar GaN layer.…”

“…A smooth surface can be achieved with the overgrowth of about 4 µm, which is faster than any other conventional ELOG techniques. 19,20 Initial X-ray diffraction (XRD) measurements have been performed as a function of azimuth angle, exhibiting that the full width at half maximum (FWHM) of on-axis XRD rocking curves measured along the [1-100] and [-1-123] directions is 320 and 260 arcsec, respectively. These represent the best results on semi-polar GaN with a similar thickness grown on sapphire.…”

“…One clear way forward, meeting the fundamental challenges, is to grow along a semi-polar direction, in particular, [11][12][13][14][15][16][17][18][19][20][21][22] direction. It has been predicted that (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) surface leads to easier accommodation of larger indium atoms than either polar-or non-polar surface, 4 favoring the growth of high indium content InGaN layers which are necessary for green or yellow emitters.…”