InGaN/GaN quantum well structures with greatly enhanced performance on a-plane GaN grown using self-organized nano-masks

Abstract

Great improvement in crystal quality of a-plane (non-polar) GaN has been achieved using a simple but effective overgrowth technique based on self-organized nano-masks. This has been confirmed by a massive reduction in full width at half maximum of x-ray diffraction rocking curves measured along both symmetrical and asymmetrical directions. Taking the advantage of utilising the nano-masks, a quick coalescence with a thickness of less than 1 μm has been obtained, which is much less than that using any conventional overgrowth techniques. The dislocation density has been significantly reduced by more than one order magnitude compared with a standard a-plane GaN layer on sapphire. An InGaN/GaN multiple quantum well (MQW) structure grown on the high quality a-plane GaN has demonstrated an enhancement with a factor of 7 in optical efficiency, compared with a similar MQW structure grown on a standard c-plane GaN layer. The excitation-power dependent photoluminescence measurements have confirmed that the a-plane InGaN/GaN MQW structure does not suffer from quantum-confined Stark effect any more.

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.…”

“…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. 14,15 Very recently, we have developed another cost-effective approach to the overgrowth of semi-polar GaN on mask-patterned micro-rod arrays on 2" sapphire, where the diameter of micro-rods with a regular patterning can be accurately controlled. 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.…”

“…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.…”

Enhanced light extraction in tunnel junction-enabled top emitting UV LEDs

“…The sample was annealed at 860 °C for 90 s under N 2 ambient to form nano-sized Ni clusters. [21][22][23][24] The self-assembled Ni nano-clusters were used as nanoscale etch masks for inductively coupled plasma reactive ion etching (ICP-RIE) of both Devices with and without surface roughening were compared on the same sample by avoiding Ni deposition in half of the sample area. The electroluminescence (EL) spectrum and emission power were measured on-wafer from the top surface of the devices at room temperature using a calibrated Ocean Optics USB 2000 spectrometer coupled with a fiber optic cable.…”