We demonstrate semipolar InGaN single-quantum-well light emitting diodes (LEDs) in the green, yellow-green, yellow and amber spectral region. The LEDs are grown on our overgrown semipolar (11-22) GaN on micro-rod array templates, which are fabricated on (11-22) GaN grown on m-plane sapphire. Electroluminescence measurements on the (11-22) green LED show a reduced blue-shift in the emission wavelength with increasing driving current, compared to a reference commercial c-plane LED. The blue-shifts for the yellow-green and yellow LEDs are also significantly reduced. All these suggest an effective suppression in quantum confined Stark effect in our (11-22) LEDs. On-wafer measurements yield a linear increase in the light output with the current, and external quantum efficiency demonstrates a significant improvement in the efficiency-droop compared to a commercial c-plane LED. Electro-luminescence polarization measurements show a polarization ratio of about 25% in our semipolar LEDs.

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.

(1120) non-polar and (1122) semi-polar GaNs with a low defect density have been achieved by means of an overgrowth on nanorod templates, where a quick coalescence with a thickness even below 1 μm occurs. On-axis and off-axis X-ray rocking curve measurements have shown a massive reduction in the linewidth for our overgrown GaN in comparison with standard GaN films grown on sapphire substrates. Transmission electron microscope observation demonstrates that the overgrowth on the nanorod templates takes advantage of an omni-directional growth around the sidewalls of the nanostructures. The dislocations redirect in basal planes during the overgrowth, leading to their annihilation and termination at voids formed due to a large lateral growth rate. In the non-polar GaN, the priority 〈0001〉 lateral growth from vertical sidewalls of nanorods allows basal plane stacking faults (BSFs) to be blocked in the nanorod gaps; while for semi-polar GaN, the propagation of BSFs starts to be impeded when the growth front is changed to be along inclined 〈0001〉 direction above the nanorods.

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A simple but cost-effective overgrowth technique has been developed for the growth of semi-polar (11-22) GaN on mask-patterned micro-rod array templates fabricated on thin (11-22) GaN layers on sapphire. As a result, a fast coalescence with a thickness of ~1 μm has been obtained. Massively improved crystalline quality has been achieved, confirmed by detailed X-ray rocking curve measurements, which show that the full width at half maximum (FWHM) has been reduced to 0.096° and 0.097° at both 0° and 90° azimuth angle measured on an overgrown sample with a total thickness of 4.5 μm. The root mean square (RMS) roughness measured by atomic force microscopy is 1.47 nm. A number of InGaN/GaN multiple quantum well (MQW) structures with high In composition have been grown on the overgrown semi-polar GaN templates, showing strong photoluminescence (PL) emission with a wavelength from 495 to 590 nm at room temperature. Temperature dependent PL measurements have been performed to estimate their internal quantum efficiency (IQE), demonstrating ~ 8% of IQE for the sample with an emission wavelength of 590 nm. Power dependent PL measurements indicate weak quantum confined Stark effects (QCSE).