Abstract
We report on the thorough investigation of light emitting diodes (LEDs) made of core-shell nanorods (NRs) with InGaN/GaN quantum wells (QWs) in the outer shell, which are grown on patterned substrates by metal-organic vapor phase epitaxy. The multi-bands emission of the LEDs covers nearly the whole visible region, including UV, blue, green, and orange ranges. The intensity of each emission is strongly dependent on the current density, however the LEDs demonstrate a rather low color saturation. Based on transmission electron microscopy data and comparing them with electroluminescence and photoluminescence spectra measured at different excitation powers and temperatures, we could identify the spatial origination of each of the emission bands. We show that their wavelengths and intensities are governed by different thicknesses of the QWs grown on different crystal facets of the NRs as well as corresponding polarization-induced electric fields. Also the InGaN incorporation strongly varies along the NRs, increasing at their tips and corners, which provides the red shift of emission. With increasing the current, the different QW regions are activated successively from the NR tips to the side-walls, resulting in different LED colors. Our findings can be used as a guideline to design effectively emitting multi-color NR-LEDs.
Highlights
By enhancement of needed contribution from spatially separated NRs of different design it is possible to improve the color purity of the LED and make it less dependent on the current density. This goal can be achieved by developing the pattern for selective area growth, comprising different elementary cells
Our findings present a platform for successful implementation of NR arrays with perfect luminescence control for full-color display application
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Summary
The NRs were grown by pulsed selective area epitaxy (SAE) in an EpiQuest showerhead MOCVD reactor. One μPL setup comprises Horiba Jobin Yvon T64000 and LabRAM HR spectrometers equipped by a Linkam THMS600 temperature-controlled microscope stage. This setup allows measuring the Raman spectra to confirm the high crystal quality of the NRs. The other μPL setup allows carrying out the PL measurements with temporal resolution to investigate the characteristic decay times. The other μPL setup allows carrying out the PL measurements with temporal resolution to investigate the characteristic decay times This setup is equipped with a single-photon avalanche photodiode (PDM-100-S0E; Micro Photon Devices) and a time-correlated single photon counting (TCSPC) module (SPC-130; Becker & Hickl) for time-resolved PL detection. The electroluminescence (EL) was recorded under CW current at room temperature with detection normally to the sample surface by an OceanOptics fiber multi-channel spectrometer
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