Growth of InGaN/GaN quantum wells with graded InGaN buffer for green-to-yellow light emitters

We have studied the growth of high-indium-content In x Ga1− x N/GaN double quantum wells (QWs) for yellow and green light emitters by plasma-assisted molecular beam epitaxy at a low substrate temperature (570 °C). By introducing a graded In y Ga1− y N buffer layer, the PL intensity of QWs can be increased sixfold compared with that of the original structure. In addition, the indium content in InGaN QWs was increased owing the prolonged growth time of the graded In y Ga1− y N buffer layer. After adjusting to optimal growth conditions, we achieved In x Ga1− x N/GaN QWs with x = 0.32. Photoluminescence measurements showed that the emission wavelength from In x Ga1− x N/GaN QWs was 560 nm (2.20 eV). The optimal condition for the gradient In y Ga1− y N buffer layer was obtained for light emission from green to yellow.