| dc.description.abstract | Recently, InGaN/GaN multi-quantum well (MQW) of blue or green light emitting diodes (LEDs) has attracted great interest in solid-state lighting. However, the efficiency droop restricts LEDs ability under the high power operation which is the critical issue. The droop makes the internal quantum efficiency has a great drop. In this study, two commercial LED structures are investigated which are vertical and lateral chip respectively. The finite element method (FEM) and Monte Carlo statistics method are applied to the optical-electrical-thermal coupled numerical model. Through the current and energy conservation, we can define every carrier behavior in active layer and heat generation. We also can obtain the light source from the calculated IQE to start the ray tracing. Then we analyze the interaction of current spreading effect on electrical efficiency, internal quantum efficiency, light extraction efficiency, junction temperature and light output power.
The experiment shows the more nonlinear increase of junction temperature and severer droop in lateral structure. By the simulation, the carrier leakage is the main mechanism from the nature of materials which induces the droop. Furthermore, current crowding also affects the quantum efficiency. In fact, current spreading is the key to drive the droop from external.
In the final part, by the optical simulation, the light extraction efficiency also plays an important role of efficiency droop, which is caused by the absorption effect. Although the current crowding of the vertical structure degree is lower, the stronger absorption by n-pad results in the greater efficiency droop, even the absorption coefficient is smaller than lateral structure. Based on these analyses of the simulation, the better LED device is expected to improve.
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