In this thesis, the structural, optical, and electrical properties of InGaN-based quantum well (QW) light-emitting diodes (LEDs) operating long-visible wavelength above 550 nm are discussed. InGaN with high indium (In) content HI-InyGa1-yN was grown by so called gallium (Ga)-flow interruption (Ga-FI) technique, where Ga flow was periodically interrupted during the growth of an InGaN layer. To extend the emission wavelength to orange-red spectral range, InxGa1-xN was used as a barrier. The epitaxial layers of HI-InyGa1-yN/InxGa1-xN QW-LED were grown on patterned sapphire substrates by using Tomas-swan metal-organic chemical-vapor deposition. The LED samples were investigated by transmission electron microscopy, High-resolution X-ray diffraction, fluorescence microscopy (FM), photoluminescence (PL), and electroluminescence (EL). An In0.34Ga0.66N/In0.1Ga0.9N-QW LED, grown by a conventional growth mode, was prepared as a reference. The epitaxial layer of the conventional In0.34Ga0.66N/In0.1Ga0.9N-QW LED (C-LED) was formed by continuously supplying Ga, In, and nitrogen (N) at the same time for both well and barrier. For the HI-InyGa1-yN well formed by the Ga-FI technique, the interruption times were 2, 3 and 5 seconds. With increasing the Ga-FI time, the emission wavelength of the LED samples was blue-shifted. We also varied the In/Ga flux ratio of the InxGa1-xN barrier of HI-InyGa1-yN/InxGa1-xN (0, 0.217, and 0.434). As the In/Ga ratio increased, the emission wavelength was red-shifted but the PL intensity decreased. The optical distribution depending on the focal plane of the FM measurements showed that the light mostly emitted around the patterns. This is related to the spatial distribution of threading dislocations and defects. As the In content of HI-InyGa1-yN/InxGa1-xN QWs increased, spatial distribution of yellow-orange light was enlarged. At the same time, green fluorescent image was additionally observed among the patterns due to non-uniform distribution of In. With increasing emission wavelength of the Ga-FI LEDs by change the flow-interruption time for HI-InyGa1-yN well and In/Ga ratio for the InxGa1-xN barrier, the PL and EL intensities were reduced mainly due to the defects and the quantum-confined stark effect (QCSE). To increase the crystal quality and reduce the QCSE for the HI-InyGa1-yN/InxGa1-xN, graded InGaN/GaN superlattice (GSL) was inserted between the n-GaN cladding layer and the HI-InyGa1-yN/InxGa1-xN QWs. The PL intensity of the HI-InyGa1-yN/InxGa1-xN LED on the GSL structure was more than 2.6 times than the LED without the GSL. The emission wavelength was also blue-shifted by inserting the GSL. This could be explained by the fact that the QCSE was reduced by inserting the strain-relaxation effect of the GSL structure. From these results, the formation of HI-InyGa1-yN using the Ga-FI technique can be an effective way to extend the emission wavelength to orange-red spectral region with little degradation of radiative efficiency.