The study on LED droop of flip-chip GaN LED

Light emitting diode (LED) is widely used in lighting field. LEDs are revolutionizing the automotive lighting industry, as they are often much more durable, efficient and energy-saving than various traditional car headlight technologies. Blue light emitted from GaN LEDs can be used to stimulate a wider spectrum of emission from the phosphor layer around the LED to create white light. Although LEDs are more efficient than previous lighting technologies, there are still some scientific and engineering challenges need to be overcame, such as with the drive current increases, the efficiency of LEDs is significant decreases. This phenomenon is known as LED droop. Therefore, in order to increase the brightness, it is necessary to use more LED chips, rather than simply increase the drive current. The cost of LED products will increase. At present, the suppression of LED droop is one of the important ways to reduce the cost of LED products. In this work, we focus on suppressing the LED droop and improving the luminous efficiency of LED. To solve above problems, a flip-chip GaN P-N junction model is investigated. The configuration is composed of a three-layer structure. Besides, the P-N junction is analyzed and optimized. The characteristics of proposed LED configuration are investigated by using finite element method (FEM). Research results show that internal quantum efficiency (IQE) drops drastically when current density exceeds 180 A/cm^2, and the luminous efficiency of the device is high when the current density is 100-180 A/cm^2.