Application Research of Micro/Nano Optics in LED Chips
Since the introduction of GaN blue LEDs in 1991, GaN-based LEDs have developed rapidly in recent years. At present, high-efficiency GaN-based LEDs have been widely used in full-color displays, solid-state lighting, and liquid crystal display backlights. The LED lighting market is growing rapidly due to its long life, low power consumption, environmental protection, impact resistance and shock resistance. However, due to the total reflection caused by the difference in refractive index between the semiconductor and the air, the light extraction efficiency of the LED surface is low. A typical GaN semiconductor material has a refractive index of 2.5, which is known by the law of total reflection, and the light escapes from the semiconductor. The critical value of the total reflection angle into the air is 24°, so light greater than 24° cannot escape from the semiconductor material. Therefore, total reflection greatly affects the light extraction efficiency of the LED. Therefore, how to reduce total reflection and improve the light extraction efficiency of LED has become one of the research hotspots. This paper mainly introduces the processing of several microstructures on the surface of LED chips or inside the chip, which can all play a role in improving the light-emitting efficiency of LEDs.
1 LED surface microstructure technology
Traditional GaN-based LEDs use chemical vapor deposition (MOCVD) technology at 560? A Si-doped n-type GaN material and a Mg-doped p-type GaN material are deposited on the sapphire substrate around C, and a quantum well (MQW) is formed between the two materials. The p-type GaN material is further coated with an ITO film (indium tin oxide) as a transparent electrode, which functions to enhance the brightness of the electrode and to isolate electron radiation emitted from the chip, which is harmful to humans, Ultraviolet light and far infrared rays [6]. The basic structure of the LED is shown in Figure 1.
Zhang Xianpeng et al. [8] of Tsinghua University fabricated a microstructure with a diameter of 3μu03BCm and a period of 6μu03BCm on the surface of p-GaN by inductively coupled plasma (ICP) etching based on Cl2/Ar/BCl3 gas. The microstructure increases the light fluorescence effect of the GaN-based blue LED chip by 42.8%% uFF0C and increases the front light extraction efficiency by 38%% when the LED device injection current is 20 mA. The backlight emission efficiency of the chip increases by 10.6%. U3002
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