Electro-optic and thermal studies of multi-quantum well light emitting diodes in InGaN/GaN/sapphire structure.

We present an electrical model for quantum-well light emitting diodes (LEDs) with a current spreading layer. The LEDs studied have a Multi-Quantum Well (MQW) between p-GaN and the n-GaN grown on sapphire. The model consists of a diode connected with a series resistor resulting from the current spreading layer. Using the model, the IN curve of the diode itself is extracted from the measured LED I-V curve. The model also includes a current equation for the diode itself which was subsequently sought to match the extracted IN curve. In the seeking process, junction temperature (T-j) rather than case temperature (T.) was used in the equation. The diode model allows one to calculate the reduction on conversion efficiency caused by the current spreading layer. Results show that the current spreading layer causes 20% of the efficiency reduction at T-j = 107 degrees C. The model can be used to optimize the conversion efficiency by balancing the transparency and the resistance of current spreading layer.