Improved quality (112¯0)a-plane GaN with sidewall lateral epitaxial overgrowth

Abstract

We demonstrate a technique to reduce the extended defect densities in a-plane GaN deposited on r-plane sapphire. The SiO2 lateral epitaxial overgrowth mask consisted of ⟨11¯00⟩GaN stripes. Both the mask and GaN were etched through the mask openings and the lateral growth was initiated from the etched c-plane GaN sidewalls, and the material was grown over the mask regions until a smooth coalesced film was achieved. Threading dislocation densities in the range of 106–107cm−2 were realized throughout the film surface. The on-axis and off-axis full width at half maximum value and surface roughness were 0.082°, 0.114°, and 0.622 nm, respectively.

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

“…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.…”

“…There is a limited number of reports on overgrowth of semi-polar GaN mainly based on conventional epitaxial lateral overgrowth (ELOG) [8][9][10][11][12][13] which generally leads to a non-uniformity issue and requests a thick overgrown layer (typically > 10 µm) in order to achieve an atomically flat surface. In order to address these issues, previously we reported an overgrowth approach based on self-organised nickel nano-masks, leading to a significant improvement in the crystal quality of either semi-or non-polar GaN on sapphire and achieving an atomically flat surface with an overgrown layer of only a few micrometers.…”

“…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.…”

“…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.…”

Defect reduction in nonpolar a-plane GaN films using in situ SiNx nanomask

“…Lateral epitaxial overgrowth ͑LEO͒ techniques have been employed in the past for achieving defect reduction in nonpolar GaN. [8][9][10] However, all of these techniques involve ex-situ processing steps and regrowths. The use of in-situ SiN x interlayer has proven to be an effective technique in defect reduction in conventional c-plane GaN.…”