Monolithic phosphor-free InGaN/GaN quantum dot wavelength converter white light emitting diodes

Abstract

We report the characteristics of phosphor-free self-organized InGaN/GaN quantum dot wavelength converter white light emitting diodes grown by plasma assisted molecular beam epitaxy. The exciting quantum dots, in which electrically injected carriers recombine, are blue-emitting and the converter dots are red-emitting. We have studied the effect of tuning the number of dot layers and the peak emission wavelength of the exciting and converter dots on the nature of the emitted white light, in terms of the chromaticity coordinates and correlated color temperature. Depending on the values of these wavelengths, color temperatures in the range of 4420–6700 K have been derived at a current density of 45 A/cm2 across multiple devices. The variation of the color temperature with change in injection current is found to be very small.

Photoluminescence studies of a perceived white light emission from a monolithic InGaN/GaN quantum well structure

“…For this reason, a lot of effort has been devoted to obtaining white emission from a monolithic system. To date, reports on achieving white emission using phosphor-free GaN-based systems have been based on: InGaN/GaN multiquantum well (MQW) structures with different In content and 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 { } and { } microfacets 13 14 , InGaN/GaN quantum dot 15 and quantum well 16 17 wavelength converter white LED heterostructures; and a defect-induced colour-tunable system based on blue InGaN/GaN MQW emission and broadband red emission in p-GaN 16 . Natural white (colour temperature ~6000 K) was demonstrated in thick InGaN nanodisks, grown on self-assembled GaN nanorod arrays, for which the numbers, positions, and thicknesses were tailored in order to get polychromatic nanodisk ensembles embedded vertically in the GaN nanorod p-n junction 18 .…”

“…Natural white (colour temperature ~6000 K) was demonstrated in thick InGaN nanodisks, grown on self-assembled GaN nanorod arrays, for which the numbers, positions, and thicknesses were tailored in order to get polychromatic nanodisk ensembles embedded vertically in the GaN nanorod p-n junction 18 . In the InGaN/GaN quantum dot wavelength converter white LED heterostructures grown by molecular beam epitaxy 15 , it was possible to achieve a 4420–6700 K correlated colour temperature (CCT) range, using an injection current density of 45 A.cm −2 , by tuning the number of quantum dots, and the emission wavelength of the emission and converter dots. In this work, we demonstrate by photoluminescence analysis warm white light emission (3260–4000 K) from a monolithic InGaN/GaN single quantum well (QW)-based high quality structure, and show that the white emission persists even after annealing at 1000 °C and at high pressure, confirming the high stability of these structures after such post-growth conditions.…”

Polarized white light from hybrid organic/III-nitrides grating structures

“…A number of approaches have been proposed in order to address these challenging issues, for instance, monolithically integrated white light LEDs34, hybrid III-nitride/colloidal quantum dots56 and hybrid III-nitride/organic conjugated polymers78. An ideal solution would be a monolithically grown white light LEDs with all emission components (at least blue and yellow) exhibiting both polarized emission properties and high efficiency.…”

Design analysis of phosphor-free monolithic white light-emitting-diodes with InGaN/ InGaN multiple quantum wells on ternary InGaN substrates

“…[6][7][8][9][10] However, it is very challenging to incorporate high In-content into InGaN/ GaN QWs on GaN substrate which is critical for green and yellow emission wavelengths due to charge separation issue from large lattice-mismatch strain. 20,21 On the other hand, nanostructure engineering approaches such as the use of quantum dots, 11,12 nanowires, 13 substrates 18,19 have also been pursued previously to achieve white LEDs. Nevertheless, these methods all require complex fabrication processes which are challenging to be implemented into large scale production.…”

“…[6][7][8][9][10][11][12][13][14][15][16][17][18][19] Previous works have reported the possibility of fabricating phosphor-free monolithic white LED by stacking multi-color-emitting InGaN/ GaN quantum wells (QWs) on GaN substrate. [6][7][8][9][10] However, it is very challenging to incorporate high In-content into InGaN/ GaN QWs on GaN substrate which is critical for green and yellow emission wavelengths due to charge separation issue from large lattice-mismatch strain.…”