Scientists from the Chinese Academy of Sciences to make use of strained quantum dots LED white light

Chen Hong Chinese academy and his research team used lattice relaxation (lattice rELaxation) to control the properties of GaN / InGaN Quantum Well (GaN/InGaN) in indium precipitation (precipitation), can make the indium gallium nitride (InGaN) grains emit light from green to white, made of white light emitting diode (LED).

In the assembly of the Academy of Sciences, the luminescence wavelength of the quantum well is about 440 nm, and the quantum dot emits a light with a wavelength of 545 nm or longer. In addition, the addition of indium can increase the size and density of the quantum dots, and in addition to the peak wavelength of the original quantum dots, another peak will be generated at 495 nm.

The team added a layer of InGaN at the bottom of the GaN/InGaN quantum well, which was originally used to collect carriers to improve the luminous intensity. In the course of the study, they try to InGaN thick film LED wafer deposited at the bottom part of the lattice relaxation, the change of the thickness of the InGaN layer, will affect the strain in GaN crystal (strain) distribution, and then change the concentration of quantum dots. When the thickness of the bottom layer is 160, 190 and 220 nm, the color of the grain is green, Huang Lvguang and white light, respectively.

The results show that the LED emission wavelength is two, and the other two are of the order of three by spectra (Electroluminescent). The proportion of indium containing three LED layer is 4.4%, the bottom of the thinnest LED retains most of the biaxial strain (biaxial-strain), Chen Hong et al. Calculation of lattice relaxation ratio of the InGaN layer is about 9.6%, by contrast, the most thick relaxation ratio up to 64.4%.

The researchers used the transmission electron microscope (TEM) observation found that, when the bottom of the InGaN is the thinnest, due to the structure is more complete, so the strain will reduce the deposition of indium containing quantum dots. The disadvantage of this method is that when the thickness of the substrate increases, the intensity of the excitation light decreases. Chen Hong et al. Argue that this is due to the dislocation caused by the high lattice relaxation (Dislocations) into the center of the nonradiative recombination (non-radiative recombination).

Chen Hong admitted that the technology to commercial production of white LED, you must first overcome the problem of consistency (uniformity) and reproducibility (reproducibility). He pointed out that the reproducibility of the wavelength depends on the composition and thickness of the underlying nGaN, so very sensitive to the temperature of the crystal.