The enhanced emission efficiency and reduced spectral shifts of a green InGaN/GaN quantum-well (QW) light-emitting-diode epitaxial structure by using the prestrained growth technique when compared with a control sample of the same emission spectrum with conventional growth are demonstrated. By adding an ∼7%-indium InGaN/GaN QW to the structure before the growth of designated emitting high-indium QWs, the growth temperature of the emitting QWs can be raised by 30 °C while keeping about the same emission wavelength around 544 nm in photoluminescence (PL) and 525 nm in electroluminescence (EL). The internal quantum efficiency, room-temperature PL intensity, and EL intensity at the injection current of 20 mA are increased by ∼167%, ∼140%, and ∼182%, respectively. Also, the spectral blueshift range in increasing injection current in the range of 50 mA is decreased by 46%. Based on the pump-power dependent PL measurement, it is found that the quantum-confined Stark effect (QCSE) becomes weaker in the prestrained growth sample. Also, from the calibration of the Arrhenius plots, the carrier localization effect is observed to become weaker under prestrained growth. Therefore, the enhanced emission efficiency is mainly attributed to the decreased defect density and the reduced QCSE in the prestrained sample.

The authors demonstrate superior crystal quality of a-plane GaN grown on r-plane sapphire substrate based on the flow modulation epitaxy (FME) technique, in which the Ga atom supply is alternatively switched on and off with continuous nitrogen supply. With the FME technique, a high growth rate of 2.3μm∕h can still be achieved. With or without epitaxial lateral overgrowth (ELOG), either c- or m-mosaic condition is significantly improved in the samples of using FME. With ELOG, the surface roughness can be reduced from 1.58to0.647nm in an area of 10×10μm2 microns by using the FME technique. Based on the results of photoluminescence measurement, one can also conclude the better optical property of the FME-grown a-plane GaN thin films. Besides, it is shown that tensile strain is more relaxed in the FME samples.