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A vertical light-emitting diode (VLED) with the CdZnO/n-ZnO quantum wells and n+-ZnO capping layer grown with molecular beam epitaxy and the p-GaN layer grown with metalorganic chemical vapor deposition, is fabricated and characterized. Its performances are compared with those of a lateral LED based on the same epitaxial structure to show the significantly lower device resistance, smaller leakage current, weaker output intensity saturation, relatively lower defect emission, and stronger emissions from the p-GaN and n-ZnO layers in the VLED.

A low-cost large-area effective sapphire substrate liftoff method based on the photoelectrochemical (PEC) etching technique is demonstrated. By preparing patterned sapphire substrate (PSS) with 1-D periodic grooves and an epitaxial structure with the grooves preserved to form tunnels, PEC electrolyte can flow along the tunnels to etch the bottom of the GaN layer for separating the PSS from the wafer-bonded epitaxial layer. Assisted by the device isolation procedure, the PSS liftoff of a quarter-wafer sample can be completed in 8 min. After a smoothing process of the exposed N-face surface after liftoff, a vertical light-emitting diode (LED) is fabricated for comparing its characteristics with those of a conventional LED.

A CdZnO/n-ZnO multiple-quantum-well (QW) light-emitting diode (LED), with the QWs and n+-ZnO capping layer grown with molecular beam epitaxy on p-GaN, which is grown with metal-organic chemical vapor deposition, is fabricated and characterized. Because of the weak carrier localization mechanism in the ZnO-based LED, its defect emission is quite strong and dominates the LED output when injection current is low. The blue shift of the LED output spectrum in applying a forward-biased voltage and the large blue-shift range in increasing injection current show the different behaviors of such a ZnO-based LED from those of a nitride LED.

The dependencies of quantum-well (QW) internal quantum efficiency (IQE) and device behaviors on the p-layer thickness in a high-indium InGaN/GaN QW light-emitting diode (LED) are demonstrated. During the high-temperature growths of the p-AlGaN and p-GaN layers, the QWs are thermally annealed to increase their IQEs and blue-shift the emission with increasing p-layer thickness. Meanwhile, the quantum-confined Stark effect is enhanced with increasing p-layer thickness to decrease the IQEs and red-shift the emission. Based on the counteraction between the two effects, the maximum IQE and the shortest emission wavelength are observed in a sample with an optimized p-layer thickness, which includes a p-AlGaN layer of 20 nm and a p-GaN layer of 60 nm in thickness under our growth conditions. The fabricated LEDs of different p-GaN thicknesses show the similar variation trends in emission efficiency and wavelength.