Current crowding effects on the thermal performance of AlGaN

Abstract

In the areas, such as automotive, outdoor, and building lighting in which high brightness is very significant, high lumen AlGaN/ GaN light emitting diodes (LED) are preferred due to their low energy consumption vs high intensity light output. Although their high energy efficiency, a large proportion of electrical energy is converted into heat and causes device temperatures to rise. It is important to solve the thermal problems of the devices as the increasing temperatures will affect the properties of the devices such as longevity, lumen flux, and wavelength. The largest heat generation mainly occurs between the p-n junction area where the highest temperature values are observed. All LED luminaire and device designs are possible with accurate detection of junction temperatures. In high lumen applications, non-uniform distribution of current density known as current crowding will affect unexpectedly high junction temperatures may exceed the safe limit and result in degradation in/around thermal hotspots. However, it is very difficult to obtain the junction temperatures of variations at high resolution with current experimental techniques. Junction temperatures can be determined more precisely with multidimensional electro-thermal models by considering the nonuniformities such as current crowding. There are very few studies in the literature where electrical and thermal models are combined. Two-dimensional electrothermal simulations based on finite-element method numerical simulation will be developed to study the electrical and thermal properties of chip level high-lumen LEDs. Junction temperature distribution of LED chips in LED array structures will be obtained considering the effects of current crowding and recombination phenomenon. Hotspot formations in the device structure due to the current crowding effect will be investigated. Simulations will be performed by the commercial software COMSOL Multiphysics Semiconductor Module.