Abstract
In this work we demonstrate by photoluminescence studies white light emission from a monolithic InGaN/GaN single quantum well structure grown by metal organic chemical vapour deposition. As-grown and thermally annealed samples at high temperature (1000 °C, 1100 °C and 1200 °C) and high pressure (1.1 GPa) were analysed by spectroscopic techniques, and the annealing effect on the photoluminescence is deeply explored. Under laser excitation of 3.8 eV at room temperature, the as-grown structure exhibits two main emission bands: a yellow band peaked at 2.14 eV and a blue band peaked at 2.8 eV resulting in white light perception. Interestingly, the stability of the white light is preserved after annealing at the lowest temperature (1000 °C), but suppressed for higher temperatures due to a deterioration of the blue quantum well emission. Moreover, the control of the yellow/blue bands intensity ratio, responsible for the white colour coordinate temperatures, could be achieved after annealing at 1000 °C. The room temperature white emission is studied as a function of incident power density, and the correlated colour temperature values are found to be in the warm white range: 3260–4000 K.
Highlights
Well thicknesses emitting in the primary colours (RGB)[8,9,10], adding Si and Zn codopants to the InGaN/ GaN structure[11], In-rich InAlGaN/InGaN heterostructures[12], InGaN/GaN MQWs grown on c-plane (0001) and on semipolar {1122} and {1101} microfacets[13,14], InGaN/GaN quantum dot[15] and quantum well[16,17] wavelength converter white light-emitting diodes (LEDs) heterostructures; and a defect-induced colour-tunable system based on blue InGaN/GaN MQW emission and broadband red emission in p-GaN16
At room temperature (RT), for the as-grown and high temperature and high pressure (HTHP)-1000 samples, the BB persists at 2.8 eV, without any shift of the peak position compared to low temperature
As-grown and HTHP annealed InGaN/GaN quantum well structures with active layer emitting in the blue region were analysed by optical techniques
Summary
The InGaN/GaN QW-based structure was grown by Metal Organic Chemical Vapour Deposition (MOCVD) on c-plane sapphire substrate. The structure is grown on a thick n-type GaN layer which is followed by the active region consisting of one 2.5 nm-thick InGaN QW with InN content of ~10%. The 325 nm line of a cw He-Cd laser (power density I0 < 0.6 W.cm−2) was used as excitation source, corresponding to an energy ~3.8 eV which is above the GaN and InGaN bandgaps. The sample luminescence was dispersed by a SPEX 1704 monochromator (1 m, 1200 gr.mm−1) and detected by a cooled Hamamatsu R928 photomultiplier. Photoluminescence excitation (PLE) and PL spectra were recorded at room temperature (RT) using a Fluorolog-3 Horiba Scientific modular apparatus with a double additive grating scanning monochromator (2 × 180 mm, 1200 gr.mm−1) in the excitation channel and a triple grating iHR550 spectrometer (550 mm, 1200 gr.mm−1) coupled to a R928 Hamamatsu photomultiplier for detection. The measurements were carried out using a front face acquisition geometry, and the presented spectra were corrected for the spectral characteristics of the optical components and the Xe lamp
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