Abstract
Broadened emission was demonstrated in coaxial GaInN/GaN multiple quantum shell (MQS) nanowires that were monolithically grown by metalorganic chemical vapor deposition. The non-polar GaInN/GaN structures were coaxially grown on n-core nanowires with combinations of three different diameters and pitches. To broaden the emission band in these three nanowire patterns, we varied the triethylgallium (TEG) flow rate and the growth temperature of the quantum barriers and wells, and investigated their effects on the In incorporation rate during MQS growth. At higher TEG flow rates, the growth rate of MQS and the In incorporation rate were promoted, resulting in slightly higher cathodoluminescence (CL) intensity. An enhancement up to 2–3 times of CL intensity was observed by escalating the growth temperature of the quantum barriers to 800 °C. Furthermore, decreasing the growth temperature of the quantum wells redshifted the peak wavelength without reducing the MQS quality. Under the modified growth sequence, monolithically grown nanowires with a broaden emission was achieved. Moreover, it verified that reducing the filling factor (pitch) can further promote the In incorporation probability on the nanowires. Compared with the conventional film-based quantum well LEDs, the demonstrated monolithic coaxial GaInN/GaN nanowires are promising candidates for phosphor-free white and micro light-emitting diodes (LEDs).
Highlights
White light-emitting diodes (LEDs), which cover the full spectral range of visible light, are regarded as an inevitable technology in illumination, micro-display and visible light communication systems [1,2,3]
In the modified growth method, the quantum-barrier was grown at high temperature (800 ◦C) to increase the crystalline quality of the coaxial GaInN/GaN structures, and the quantum wells were grown at low temperature to enhance the In incorporation without the risk of reducing the multiple quantum shell (MQS) quality
The pitches of the combined patterns can be optimized for longer or shorter wavelength emission, because the In incorporation rate related to the probability of diffused precursors from SiO2 mask toward NWs
Summary
White light-emitting diodes (LEDs), which cover the full spectral range of visible light, are regarded as an inevitable technology in illumination, micro-display and visible light communication systems [1,2,3]. Selective-area growth improves the quality of GaInN/GaN nanostructures, and the control of the indium (In) composition on different facets enables multi-colored emission These properties are important for realizing monolithic white LEDs on a single chip. Inspired by the modified growth method of planar a-plane multiple quantum wells [33], it is expected that by raising and lowering the growth temperature of the barriers and wells, respectively, we could enhance both the In incorporation and the crystalline quality of coaxial GaInN/GaN NWs. In this work, we comprehensively investigated multiple NW structures monolithically grown by MOCVD. In the modified growth method, the quantum-barrier was grown at high temperature (800 ◦C) to increase the crystalline quality of the coaxial GaInN/GaN structures, and the quantum wells were grown at low temperature to enhance the In incorporation without the risk of reducing the MQS quality. After characterization the morphology and optical features of the NW samples, we analyzed the effect of triethylgallium (TEG) flow rate, barrier growth temperature, and well growth temperature on the In incorporation in the MQS NWs
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