Tuning the emitting wavelength of InGaN/GaN superlattices from blue, green to yellow by controlling the size of InGaN quasi-quantum dot

High quality blue, green and yellow LEDs comprised of stable indium-rich clusters in InGaN/GaN multiple quantum wells (MQWs) have been successfully grown by metal-organic chemical vapor deposition. We show that the common degradation phenomenon on crystallinity can be avoided by these quasi-quantum dots as obtained from the integrated results of high resolution transmission electron microscopy (HRTEM), rocking curve and ω-scan analysis. Ultra-small sized indium clusters of 2 nm, 2.5 nm and 3 nm in diameter have been observed in the quantum wells from HRTEM analysis. We also show that by well controlling the dot size in the active layers, emitting wavelength in full visible light spectrum is achieved. In addition, several interesting observations were also found during analysis. First, the propagation of threading dislocations would be efficiently stopped by the quasi-dots, which behave as real quantum dots. Secondly, the thickness dependence of phase separation has also been demonstrated in the sample emitting blue light where the quantum well thickness ranges in 1.7∼2 nm and nominal In content is in 8∼10% regime. Thirdly, the phase separation is independent of film polarity (Ga-polarity or N-polarity).