Investigation of efficiency droop for UV LED with N-type AlGaN layer

Po-Min Tu; Jet-Rung Chang; Shih-Cheng Huang; Shun-Kuei Yang; Ya-wen Lin; Tzu-Chien Hung; Chih-Peng Hsu; Chun-Yen Chang

doi:10.1117/12.908266

6 February 2012 Investigation of efficiency droop for UV LED with N-type AlGaN layer

Po-Min Tu, Jet-Rung Chang, Shih-Cheng Huang, Shun-Kuei Yang, Ya-wen Lin, Tzu-Chien Hung, Chih-Peng Hsu, Chun-Yen Chang

Proceedings Volume 8278, Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVI; 82781B (2012) https://doi.org/10.1117/12.908266
Event: SPIE OPTO, 2012, San Francisco, California, United States

Abstract

The efficiency droop in InGaN-based 380nm UV light emitting device (LED) with n-GaN and n-AlGaN underlayer grown on sapphire substrate by metal-organic chemical vapor deposition (MOCVD) was investigated. From simulation result of high resolution x-ray diffraction (HRXRD) ω-2θ curve by using dynamical diffraction theory, the Al composition in the n-AlGaN layer was determined to be about 3%. The experimental results of temperature dependent photoluminescence (PL) demonstrated that the internal quantum efficiency (IQE) of n-GaN and n-AlGaN UV-LEDs are 43% and 39%, respectively, which are corresponding to an injected carrier density of 8.5 × 10¹⁷ #/cm³. It could be explained that the crystal quality of n-GaN is better than of n-AlGaN. In addition, the observation of pit density from atomic force microscopy (AFM) surface morphology is consistent with the interpretation. It was well-known that the pits appearing on the surface in the virtue of the threading dislocations. Thus, it means that defects induce the non-radiative centers and deteriorate the IQE of the UV-LED with n-AlGaN underlayer. Therefore, the light output power of n-GaN UV-LED is slightly higher below the forward current of 250 mA. Nevertheless, the output power was enhanced about 22% as the injection current was increased to 600 mA. Furthermore, the external quantum efficiency (EQE) of n-AlGaN UV-LED was nearly retained at the 600 mA (only 20% droop), whereas the UV-LED with n-GaN exhibits as high as 33%. We attributed this improvement to the less self-absoption by replacing n-GaN underlayer with n-AlGaN.

Citation Download Citation

Po-Min Tu, Jet-Rung Chang, Shih-Cheng Huang, Shun-Kuei Yang, Ya-wen Lin, Tzu-Chien Hung, Chih-Peng Hsu, and Chun-Yen Chang "Investigation of efficiency droop for UV LED with N-type AlGaN layer", Proc. SPIE 8278, Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVI, 82781B (6 February 2012); https://doi.org/10.1117/12.908266

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