Vertical structure LED: development trend of semiconductor lighting

1.

At present, the world has entered the "energy saving" era, countries are actively looking for emerging industries of energy saving and environmental protection, lighting energy consumption accounted for more than 20% of total energy consumption, therefore, reduce lighting electricity is an important way to save electricity. LED energy-saving lamp is a new generation of solid cold light source, with low energy consumption, long life, easy to control, safety and environmental protection, is an ideal energy-saving environmental protection products, suitable for a variety of lighting. However, at present, LED has not yet entered into the general lighting, one of the main reasons is that the LED (lm/$) is too low, the market needs to quickly improve the performance of LED program. There are two ways to improve the cost of LED, one is to improve the luminous efficiency of LED, and the two is to reduce the production cost of LED. However, the efficiency and the speed of the decline in the cost of the market is still not up to the LED price expectations. However, the vertical structure of LED can guarantee a certain luminous efficiency under the premise of using a larger current to drive a vertical structure of the LED chip can be equivalent to several formal structure of the chip, equivalent to a fraction of the cost of only formal structure. Therefore, the vertical structure of LED will accelerate the application of LED in the field of general lighting, the market is the inevitable trend of the development of semiconductor lighting.

2, GaN based vertical structure of the advantages of LED

According to the structure of LED, GaN based LED can be divided into formal structure, inversion structure and vertical structure. At present, more mature III nitrides are mostly made of sapphire material, because of the insulating property of the sapphire substrate, the common GaN based LED adopts the formal structure. As shown in Figure 1, the light emitted from the active region is emitted by the P type GaN region and the transparent electrode. The structure is simple and the manufacturing process is relatively mature. However, formal structure of LED has two obvious shortcomings, the first formal structure of LED electrode in LED P and N on the same side, the current must flow horizontally through the n-GaN layer, leading to local current crowding, high calorific value, limiting the driving current; secondly, due to poor thermal conductivity of sapphire substrate (35W/ (M? K)). Serious heat loss.

In order to solve the heat problem, the United States Lumileds Lighting invented the flip chip (Flipchip) technology. Schematic diagram of the structure as shown in Figure 2, this method is suitable for the preparation of the first large size LED chip eutectic welding at the same time, the corresponding size of the prepared silicon plate, and make the eutectic metal conductive layer welding electrode and a conductive layer on the lead (ultrasonic gold wire ball joint). Then, the large size LED chip is welded together with the silicon substrate by a eutectic welding device. The effect of the structure on the heat dissipation has been greatly improved, but the general GaN based on the structure of the LED is still a transverse structure, the phenomenon of the current congestion exists, still limits the further improvement of the driving current.

Two problems of vertical structure can effectively solve the formal structure of LED, the vertical structure of GaN based LED with high thermal conductivity substrate (Si, Ge and Cu to replace the sapphire substrate), largely improves the cooling efficiency; two electrodes of the LED chip with vertical structure respectively in LED epitaxial layers on both sides of the n. The electrode through the graphical, makes the current almost entirely vertical flow through the LED epitaxial layer, the current transverse flow rarely, can avoid the current formal structure congestion problem, improve the luminous efficiency, but also solve the problem of P shading, enhance the luminous area of LED.

Method of making 3, the vertical structure of LED

The most important difference between the GaN based vertical structure LED process and the LED process is that the vertical structure LED needs to introduce the substrate transfer technology. The so-called substrate transfer technology is the use of high thermal conductivity and high conductivity of the new substrate to replace the original growth substrate. The process consists of two steps, firstly using wafer bonding or plating new substrate and epitaxial wafer bonded together, and then use laser stripping, grinding and wet etching method will remove the original growth substrate.

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