This study concerns the characteristics of white GaN-based light-emitting diode (LED) on flexible substrates. The thin film GaN-based blue LEDs were directly transferred from sapphire onto the flexible polydimethylsiloxane (PDMS) substrates by laser lift-off (LLO) process. The PDMS substrates were incorporated 10–40% cerium doped yttrium aluminum garnet phosphor, YAG:Ce3+, and formed the GaN-based white LEDs. The white LEDs prepared by the GaN-based LEDs on the YAG-PDMS substrates reveal one peak at 470 nm corresponding to the emission of the GaN-based LED and a broadband included five weak peaks caused by YAG:Ce3+ phosphors.
LEDs are regarded as the most important light source in next-generation solid-state lighting to advantages in energy efficiency, long life, high reliability, and multiple applications [
Several approaches have presented flexible light-emitting diodes (F-LEDs) by transferring microstructured GaAs/GaN to flexible substrates [
In this study, we have prepared a polydimethylsiloxane (PDMS) as a substrate which had the advantages of being flexible, low cost, good chemicophysical properties and being good optically transparent. The fabrication of thin film GaN-based light-emitting diodes (GaN-based LEDs) was transferred from sapphire to flexible substrate by LLO method and produced the white light-emitting diode device.
PDMS solution was produced by mixing silicone resin agent (A agent) and curing agent (B agent) into liquid in weight ratio for 10 : 1. Then, the yellow phosphor was incorporated into the PDMS solution and stirred uniformly. Afterward, the PDMS incorporated YAG phosphor solution was placed in a vacuum chamber for 30 min so that bubbles disappeared. Polytetrafluoroethene (PTFE) is sprayed on the sapphire substrate to avoid PDMS sticking on sapphire. Then, PDMS was uniformly coated on a sapphire substrate by spin coater (speed of 300 rpm and a coating time of 40 sec). Subsequently, the PDMS substrate was treated at temperature of 120°C for 30 min to produce PDMS substrate. Finally, the cured PDMS substrate incorporated YAG phosphor (YAG-PDMS substrate) was removed from the sapphire substrate to produce white LED.
The GaN-based light-emitting diode comprised a 3
(a) Surface of the n-GaN epitaxial layer after KOH solution etching and (b) GaN-based LED after LLO process was mounted on flexible YAG-PDMS substrate.
Figure
Figure
Transmittance spectra of YAG-PDMS substrates with various YAG incorporation amount.
Figure
EL spectra obtained with different incorporation amount.
The color of EL is nearly white, as shown in Figure
Operating photos of LED on YAG-PDMS substrates with various incorporation amounts: (a) 10%, (b) 20%, (c) 30%, and (d) 40% concentration of phosphor.
Chromaticity coordinates of the GaN-based LEDs on the YAG-PDMS substrates.
In summary, characteristics of white GaN-based LEDs on YAG-PDMS substrates are reported. The white light may have contributed to the wide emission band ranging from 400 to 750 nm. The chromaticity coordinates of the YAG phosphors at 10, 20, 30, and 10% in YAG-PDMS substrates are presented in the CIE chromaticity diagram. With the increasing incorporated concentration of YAG, the chromaticity coordinates move in white light area from
The authors declare that there is no conflict of interests regarding the publication of this paper.
Financial support of this paper was provided by the Ministry of Science and Technology, China, under Contract no. NSC 103-2221-E-027-029-MY2.