We have investigated the temperature dependence of electrical and output performance of InGaN/GaN multiple-quantum well (MQW) light-emitting diodes (LEDs) with different indium compositions in the InGaN/GaN MQWs. With increasing In composition in the MQWs, the output performance of the LEDs at room temperature was increased due to a deeper potential barrier for the carriers to escape from the MQWs and the localized energy states caused by a In composition fluctuation in MQWs. However, it was found that the output performance depends on the In composition in InGaN/GaN MQWs with increasing temperature from room temperature. With increasing temperature, the output power for LED with a relatively higher In composition in the MQWs was decreased more rapidly compared to that of LED with a lower In composition in the MQWs due to the increased nonradiation recombination through the high defect densities in the MQWs resulted from the increased accumulation of strain between InGaN well and GaN barrier.
To improve the escape of photons from an LED structure, we fabricated nano-sized cavities on a p-GaN surface utilizing Pt self-assembled metal clusters for an etch mask. Wet and dry etching processes were employed to produce nano-sized cavities on the p-GaN surface. The dry etching process produced cavities with diameters ranging from 200 nm to 450 nm and from 30 to 80 nm in depth, respectively. The wet etching process, however, produced small size cavities with a size of 5 ~ 6 nm. Electroluminescence measurement showed that the relative optical output powers are increased by 88% as evidenced by frontside measurement compared to those of LEDs with no nano-sized cavities. In addition, the electrical performance was also improved as evidenced by the I-V characteristic curves. This enhanced performance can be attributed to an enhancement in light escaping due to the increased light emitting area as the result of the surface cavities and also to the reduced contact resistance due to the increased contact area.
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