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Dual-wavelength switchable emission has been demonstrated in InGaN quantum dot (QD) micro-cavity light-emitting diodes (MCLEDs). By simply modulating the injected current levels, the output of the device can be dynamically tuned between the two distinct cavity modes at 498.5 and 541.7 nm, exhibiting deterministic mode switching in the green spectral range. Owing to the microcavity effect, high spectral purity with a narrow linewidth of 0.21 nm was obtained. According to the experimental and theoretical results, it can be concluded that the dual-wavelength switching for the investigated MCLEDs is ascribed to the broad and tunable gain of a thin InGaN QD active region, together with the mode selection and enhancement effect of the cavity. To provide additional guidelines for controllable dual-wavelength switchable operation in nitride-based light-emitting devices, detailed design and fabrication strategies are discussed. This work presents an effective method to achieve mode switching for practical applications such as multi-wavelength optical recording, frequency mixing, flip-flop and optical switches.

The realization of red-emitting InGaN quantum well (QW) is a hot issue in current nitride semiconductor research. It has been shown that using a low-Indium (In)-content pre-well layer is an effective method to improve the crystal quality of red QWs. On the other hand, keeping uniform composition distribution at higher In content in red QWs is an urgent problem to be solved. In this work, the optical properties of blue pre-QW and red QWs with different well width and growth conditions are investigated by photoluminescence (PL). The results prove that the higher-In-content blue pre-QW is beneficial to effectively relieve the residual stress. Meanwhile, higher growth temperature and growth rate can improve the uniformity of In content and the crystal quality of red QWs, enhancing the PL emission intensity. Possible physical process of stress evolution and the model of In fluctuation in the subsequent red QW are discussed. This study provides a useful reference for the development of InGaN-based red emission materials and devices.