Thermal and electrical study on ac light-emitting diode with quantum wells under various cooling rate

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.The conventional Shockley equation is inappropriate to describe the relationship between the current density and the forward voltage drop across the p-n junction in LED (light-emitting diode) with multiple quantum wells. In the present study, a semi-empirical model based on the existing experimental measurements is proposed to evaluate the forwards voltage drop under given current density and temperature. The numerical model then is employed to investigate the electrical and temperature fields on ac LED with multiple quantum wells under various cooling rate. The numerical results reveal that the temperature of the LED oscillates under ac electrical potential. The temperature increases due to the heat generation arising from the electrical current across the p-n junction when the electrical potential exceeds the threshold voltage. Otherwise, there is no electrical current and thus the temperature decreases due to the effect of the cooling device. Both light-emitting power and maximum temperature increase as expected when the applied ac electrical potential increases. Fortunately, the temperature of the LED can be efficiently controlled by increasing the cooling rate. Although increasing the cooling rate would decrease the light-emitting power, the influence is not significant.