8 mA. After that point, the external quantum efficiency decreased fast, known as efficiency droop which was studied a lot in GaN-based LED. However, the external quantum efficiency of the LEDs with Au-coated SACNT was still a little bit higher than that of LEDs without

SACNT due to the current spreading. The optical output power at current injection of 20 mA for LEDs with Au-coated SACNT was improved about 9.6% and 19% compared with LEDs Saracatinib nmr without and with SACNT thin film. The 10% optical power difference between the LEDs with and without SACNT was consistent with the optical transmittance measurement results. Figure 6 The optical output power and its external quantum efficiency dependence on the current injection. The inset of Figure 6 showed the PF299 purchase measured peak wavelength shift with the current injection. The peak wavelength for LEDs with SACNT, Au-coated SACNT, and without SACNT was 634, 633.8, and 633.2 nm at 20 mA, respectively. Correspondingly, the wavelength red shift was 7.8, 7, and 7.8 nm from 10 to 100 mA, respectively, which indicated better thermal performance

for LEDs with Au-coated SACNT due to the relatively effective current spreading. The improvement of optical output power for LEDs with Au-coated SACNT thin film was due to the sheet resistance competition with the p-GaP, although there existed about 20% optical transmittance loss. According to the estimation, the sheet resistance of p-GaP in this experiment is about

300 to 500 Ω. When the Au-coated SACNT thin film was put on the p-GaP, lots of carriers could spread second outside the opaque metal electrode, which could have the possibility to contribute to the optical output power. The 2-nm-thick Au coating on the SACNTs could form the Au nanowire which may induce an ROCK inhibitor interacting electromagnetic field with multiple quantum wells (MQWs). However, this interaction is a near-field effect. Considering the distance between of Au nanowire and quantum wells in this experiment, output enhancement due to the surface plasmon resonance can be ignored. So further decreasing the sheet resistance and improvement the optical transmittance of the current-spreading layer of SACNT thin film could increase the optical output power. Conclusions The SACNT as current-spreading layer on AlGaInP LEDs was demonstrated. The voltage bias at 20 mA decreased at 0.15 V for LEDs with Au-coated SACNT, and the optical power increased about 10% compared with LEDs without SACNT due to the relatively effective current spreading. Based on the mature SACNT fabrication technique and optical transmittance performance, it is expected that SACNT could be utilized as a current-spreading layer for AlGaInP LEDs with wavelength regions from 560 to 650 nm. Acknowledgements This work was supported by National Natural Science Foundation of China (61222501 and 61335004). And thanks to Dr. Y. Lu and Miss L. Ma for the useful discussion and technique help. References 1.