Author:adminFrom未知
Date:2018-09-10 20:11
Recently, in its semi-annual report of 2018, Lyard Optoelectronic Co., Ltd., the world's leading small-pitch television company, disclosed that its Mini LED products had been developed and entered the pilot stage. It also set up a joint laboratory with Saphlux, a start-up company, to solve the problem of mini/micro LED wafers using the semipolar GaN material of Saphlux. Wavelength consistency and peak shift.
The traditional GaN based blue and green LED chips will produce peak wave (color) offset when the current changes. Micro/Mini LED has a high contrast and needs frequent scene conversion in many applications, which results in dramatic changes in driving current and peak shift.
For example, portable devices such as VR and AR (such as Google Glasses) have an average brightness of about 1 nit at night, whereas in daylight they require 500 to 700 nit. From the test data, with the change of current, the peak shift of green light of Mini / Micro LED can exceed 20 nm, which brings obvious color drift and seriously affects the display effect. In the case of green peak shifting 20nm, the color rendering of mini LED is shown in the following figure:
The peak shift is mainly caused by the inherent polarization field in the C-plane gallium nitride material: it makes the band of the quantum well tilt, so with the increase of current (electrons, holes), the band will be flattened, resulting in widening of the energy gap, resulting in the increase of photon energy and wave peak shift.
Peak shift is a common problem in blue and green LEDs in GaN system, especially in green light (high indium content leads to more tilted bands) and low current (more tilted initial bands).
Semi polar Gan is a new GaN material with a C angle Gan. By changing the crystal orientation, semipolar materials can fundamentally improve the binding rate of electrons and holes, greatly reduce or eliminate the polarization effect, so that the band is flat, the electron and hole composite rate is high. Using this characteristic, the semi-polar micro/Mini LED can maintain the band gap width when the current changes, greatly reducing the peak shift and maintaining color stability.
In addition, the small size of the micro/mini LED chip leads to the difficulty and high cost of wavelength sorting, so the wavelength consistency of the entire wafer has higher requirements. Semipolar LED has simpler epitaxial structure than traditional materials, and it is easier to achieve better wafer wavelength consistency, which greatly reduces the separation cost.
Semi polar GaN has so many advantages, but it has not been able to achieve large-scale industrial application. The essential reason is that the industry has not been able to find mass production methods for high quality semi polar Gan materials.
After nearly a decade of research and development, Saphlux, a Yale-based company, achieved a technological breakthrough by using its unique surface-controlled epitaxy. At the beginning of this year, it produced 4 inches of semi-polar gallium nitride and successfully lit up semi-polar blue and green LEDs with small peak shift and good consistency.
It is understood that, in addition to the joint laboratory with Liard Optoelectronics, Saphlux has also established cooperation with a number of international famous enterprises to provide semi-polar light source solutions to help the development of Mini/Micro LED display technology.
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