The efficiency droop of InGaN/GaN(InGaN) multiple quantum well (MQW) light emitting diodes (LEDs) with thin quantum barriers (QB) is studied. With thin GaN QB (3 nm–6 nm thickness), the efficiency droop is not improved, which indicates that hole transport cannot be significantly enhanced by the thin GaN QBs. On the contrary, the efficiency droop was remarkably reduced by using a InGaN staircase QB (InGaN SC-QB) MQWs structure where InGaN SC-QBs lower the transport energy barrier of holes. The efficiency droop ratio was as low as 3.3% up to 200 A/cm2 for the InGaN SC-QB LED. By using monitoring QW with longer wavelength we observe a much uniform carrier distribution in the InGaN SC-QB LEDs, which reveals the mechanism of improvement in the efficiency droop.

High-quality gallium nitride (GaN) film was grown on nano-patterned sapphire substrates (NPSS) and investigated using XRD and SEM. It was found that the optimum thickness of the GaN buffer layer on the NPSS is 15 nm, which is thinner than that on micro-patterned sapphire substrates (MPSS). An interesting phenomenon was observed for GaN film grown on NPSS:GaN mainly grows on the trench regions and little grows on the sidewalls of the patterns at the initial growth stage, which is dramatically different from GaN grown on MPSS. In addition, the electrical and optical properties of LEDs grown on NPSS were characterized.

InGaN/GaN triangular shaped multiple quantum wells (MQWs) grown on sapphire substrate were adopted as an active layer of light-emitting diodes (LEDs) by modulating In content in well layers. The temperature dependence of the normalized integrated photoluminescence (PL) intensity showed that the overlap of the electron and hole wave-functions of the LEDs with triangular shaped MQW is much higher than that of the LEDs with conventional rectangular MQW structures, which improves the internal quantum efficiency (IQE) to a certain degree. On the other hand, it was found that the blue shift of the peak energy as a function of injection current is improved for the device with triangular shaped MQW structure from the electroluminescence (EL) spectra of the two series devices. The comparison above indicates that the triangular MQW LEDs are more efficient and more stable.