Author: jiangwei68
Although gallium nitride based III-V semiconductors have some serious drawbacks, such as high dislocation density and strong polarization effects, they have become a promising source material. Recently, GaN-based light-emitting diodes ( LEDs ) are rapidly expanding their applications, especially in areas that require ultra-high brightness, such as large-size screen backlight units and solid-state lighting systems that replace traditional fluorescent and incandescent bulbs. Therefore, in order to meet the requirements of advanced applications, it is very important to achieve high efficiency. To make a high-efficiency LED, you should carefully optimize the internal and external structure of the LED.
1. Internal structure
The internal structure of the LED is closely related to internal quantum efficiency (IQE), linearity of light intensity and injection current (LI), forward voltage (Vf), and electrostatic (ESD).
(1) Internal quantum efficiency (IQE): It is known that the IQE of an InGaN-based LED is mainly affected by dislocation density, a piezoelectric field in a multiple quantum well, and a lateral shape of a quantum well. Many research groups are working on non-polar and polar GaN substrates to maximize IQE by reducing dislocations and polarization effects. The lateral shape of the quantum well can be controlled by growth conditions such as a strain relaxation layer under quantum and thermal annealing in two temperature growths.
(2) LI linearity: LI linearity is an important issue for LEDs under high current operating conditions. In order to improve the linearity of the LI, the non-radiative recombination caused by the overflow and defects of the high-current working condition download stream should be minimized. The overflow of the carriers can be reduced by the AlGaN electron and hole blocking layer having a higher energy band. The carrier localization effect formed by the barrier fluctuations in the quantum well helps to increase the carrier limit and reduce the defect effect.
(3) Forward voltage (Vf): Although the forward voltage is mainly determined by the energy band of the material, it is also affected by the transport barrier of the carriers in the quantum well and the resistance of the N-type and P-type GaN thin layers. Therefore, the inclusion of the quantum barrier in the quantum well can effectively reduce Vf. However, in order to excessively dope silicon and magnesium to lower the sheet resistance of N-type and P-type GaN, the crystal quality will be lowered. Excessive silicon doping (intermediate range of 10 19 cm -3 ) will cause high compressive stresses in the N-type GaN layer and form surface cracks. In addition, the use of magnesium doping exceeding 10 20 cm -3 produces inverse pyramidal inversion domain boundary (IDB) defects. Therefore, modulation doping and improved carrier mobility may be a solution to reduce the GaN crystal sheet resistance and achieve good crystal quality.
(4) Electrostatic (ESD): Gallium nitride LEDs have high dislocation density ( 10 8 ~
2, the external structure
LED-optimized external structures can improve performance such as light extraction efficiency (LEE), thermal effects, current spreading, and ESD.
(1) Light extraction efficiency (LEE): Techniques for improving light extraction efficiency can be classified into three types, namely, chip molding, surface texture (roughening), and pattern substrate (PS). Chip forming techniques include substrate shaping to change the direction of light and epitaxial layer formation for forming small angular angle reflections to direct planar light to the surface. Surface texture (roughening) can be performed by various methods such as forming a high-density V-shaped pit on the surface by low-temperature growth, submicron protrusion using a self-mask, photonic crystal or self-mask dry and wet etching. In addition, PS is also a promising technology for manufacturing high-efficiency LEDs. The LEE of the PS depends on the shape, height, size, and overall layout of the graphic. In addition to light extraction efficiency, PS can also reduce dislocation density by lateral coverage growth.
(2) Thermal effect: Thermal management of LEDs is a sensitive issue for high power LEDs. Sapphire substrate LEDs, chip flip-chip structures and backside metal (BSM) are commonly used to improve heat dissipation. For more efficient heat dissipation, vertical structure LEDs with a highly thermally conductive support layer are a good solution.
(3) Current Diffusion: Current crowding in lateral structure devices seriously affects device reliability and IQE. In the lateral device structure, the design of the lithographic pattern and the sheet resistance of the transparent electrode metal (TM) are key factors for uniform current spreading. The sheet resistance of TM should be balanced with the N-type GaN layer.
(4) Electrostatic discharge (ESD): As explained in the internal structure section, ESD is an important parameter for achieving reliable operation of LEDs. A protective diode is typically connected to the main LED and is turned on when there is a reverse peak. Silicon Zener diodes are commonly used for this function, and can also be achieved by integrating GaN reverse LEDs with the main LED.
(Editor: Yu Zhantao)
We custom Etching Cutting Die, Etching Metal Crafts, Etching Eyeglass Frames, Etching Plate Heat Exchanger Sheet with drawings provided by customers. We are equipped with professional metal etching equipment and exposure development equipment. The raw material we more use for these products is stainless-steel, brass, titanium and titanium-palladium. We can guarantee that our half etching plate heat exchanger sheet have straight surface line, and have no burr, high product accuracy.
Etching Cutting Die,Etching Metal Crafts,Etching Eyeglass Frames,Etching Plate Heat Exchanger Sheet
SHAOXING HUALI ELECTRONICS CO., LTD. , https://www.cnsxhuali.com