Great progress has been made in research on LED light extraction efficiency and reliability.

LED heat source and heat conduction LED light-emitting mechanism relies on electrons to generate light between energy bands, and the spectrum does not contain infrared components. Therefore, the generated heat cannot be emitted by radiation, so LED is a cold light source. The following is a discussion of the generation of heat and the conduction inside the system. The basic structure of an LED is a semiconductor PN junction. When current flows through the PN junction, not all of the added electrical energy is converted into light energy, and most of it remains in the form of thermal energy on the PN junction, causing the temperature of the PN junction to rise. Junction temperature. For the thermal management of LEDs, it is mainly divided into two parts: heat dissipation and heat dissipation, namely heat conduction and heat dissipation. A typical LED structure and its internal heat flow, such as the thermal resistance of the LED chip to the solder layer, is the thermal resistance of the solder layer to the substrate, R is the thermal resistance of the substrate to the thermal interface material, and R is the thermal interface material to The thermal resistance of the heat sink is the thermal resistance of the heat sinking to the surrounding environment.

In order to reduce the junction temperature of the LED chip, it is necessary to reduce the thermal resistance of each heat conduction link. LED substrate material LED chip is the core working part of the whole LED system, and is also the source of heat generation. Improving the substrate in direct contact with the chip is the main method to improve the heat dissipation performance of the chip. There are four basic principles for selecting the substrate material. The bottom is matched with the structure of the epitaxial film; 2 the substrate is matched with the thermal expansion coefficient of the epitaxial film; 3 is matched with the chemical stability of the epitaxial film; 4 the difficulty of the material preparation and the cost. Silicon (Si) is the earliest substrate material used, which has the advantages of low cost, good electrical and thermal conductivity, etc., but its thermal expansion coefficient is too different from that of the chip material gallium nitride (GaN), which is prone to cracking. Guo Lunchun et al inserted AlAlN. The buffer layer grows GaN on Si, and a GaN material having a small crack density is obtained. Domestic Nanchang University has made great progress in the research on the light-emitting efficiency and reliability of GaN-based blue LEDs with Si as the substrate.