“LED junction temperature” is not so familiar to most people, but even for people in the LED industry! Now let’s explain in detail. When the LED works, the following conditions can promote the junction temperature to rise in varying degrees.

1、 It has been proved by many practices that the limitation of light output efficiency is the main reason for the increase of LED junction temperature. At present, advanced material growth and component manufacturing technology can convert most of the input electric energy of led into light radiation energy. However, due to the much larger refractive index of LED chip material compared with the surrounding medium, most photons (> 90%) generated in the chip cannot smoothly overflow the interface, and total reflection occurs at the interface between the chip and the medium, It returns to the inside of the chip and is finally absorbed by the chip material or substrate through multiple internal reflections, and becomes heat in the form of lattice vibration, which promotes the rise of junction temperature.

2、 Because the p-n junction cannot be extremely perfect, the injection efficiency of the element will not reach 100%, that is, when the LED works, in addition to injecting charge (hole) into the n area in the P area, the n area will also inject charge (electron) into the P area. Generally, the charge injection of the latter type will not produce optoelectric effect, but will be consumed in the form of heating. Even the useful part of the injected charge will not all become light, and some will eventually become heat when combined with impurities or defects in the junction region.

3、 The poor electrode structure of the element, the material of the window layer substrate or junction area and the conductive silver glue all have a certain resistance value. These resistances are stacked with each other to form the series resistance of the LED element. When the current flows through the p-n junction, it will also flow through these resistors, resulting in Joule heat, resulting in the increase of chip temperature or junction temperature.

Of course, with the progress of science and technology, the main reason why we can’t understand the above phenomena one by one is that we can’t understand them one by one in the future. Of course, we can’t understand them one by one with the progress of science and technology!