Abstract
Self-assembled growth of blue-green-yellow-red InGaN quantum dots (QDs) on GaN templates using plasma-assisted molecular beam epitaxy were investigated. We concluded that growth conditions, including small N2 flow and high growth temperature are beneficial to the formation of InGaN QDs and improve the crystal quality. The lower In/Ga flux ratio and lower growth temperature are favorable for the formation of QDs of long emission wavelength. Moreover, the nitrogen modulation epitaxy method can extend the wavelength of QDs from green to red. As a result, visible light emissions from 460 nm to 622 nm have been achieved. Furthermore, a 505 nm green light-emitting diode (LED) based on InGaN/GaN MQDs was prepared. The LED has a low external quantum efficiency of 0.14% and shows an efficiency droop with increasing injection current. However, electroluminescence spectra exhibited a strong wavelength stability, with a negligible shift of less than 1.0 nm as injection current density increased from 8 A/cm2 to 160 A/cm2, owing to the screening of polarization-related electric field in QDs.
Highlights
In recent years, red-green-blue (RGB) micro light-emitting diode has been considered a promising display technology with many excellent features such as high luminescent efficiency, quick response, and long lifespan [1,2]
We investigated the inherent relationship between morphology and optical properties of InGaN quantum dots (QDs) and growth parameters by atomic force microscopy (AFM), photoluminescence (PL) and time-resolved PL (TRPL)
Carriers’ lifetime as both τ1 and τ2 of three InGaN QDs samples decreased with increasing temperature, which the key parameter of semiconductor materials wasrecombination measured by TRPL, and wasperformance mainly attributed to the thermal activation of more nonradiative centers
Summary
In recent years, red-green-blue (RGB) micro light-emitting diode (micro-LED) has been considered a promising display technology with many excellent features such as high luminescent efficiency, quick response, and long lifespan [1,2]. InGaN-based green LED that used multi-quantum wells (MQWs) as active regions has been suffering from the “green gap” and “efficiency droop” problems; they generally exhibit emission peak wavelength shift and color purity [6–8]. This is mainly due to the poor polarization field strength and crystal quality of InGaN materials with high In. Nanomaterials 2022, 12, 800. A variety of methods have been adopted to grown red and near-infrared InGaN QDs, including surface pretreatment, introducing the InGaN QW-QD coupled nanostructure, growth interruption method and photoelectrochemical etched quantum dot templates [17–20] Despite such achievements, there remains many challenges to be conquered for self-assembled. A green InGaN QDs LED that was prepared and exhibited a strong wavelength stability with injection current
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