Title: Enhancing the Emission Efficiency of In(0.2)Ga(0.8)N/GaN MQW Blue LED by Using Appropriately Misoriented Sapphire Substrates
Authors: Li, Zhen-Yu
Uen, Wu-Yih
Lo, Ming-Hua
Chiu, Ching-Hua
Lin, Po-Chun
Hung, Chih-Tsang
Lu, Tien-Chang
Kuo, Hao-Chung
Wang, Shing-Chung
Huang, Yen-Chin
Department of Photonics
Issue Date: 1-Jan-2009
Abstract: In this paper, we report the fabrication of an In(0.2)Ga(0.8)N/GaN multiple-quantum-well (MQW) structure on vicinal sapphire substrates with a very small offset angle of 0-1 degrees by low-pressure metallorganic chemical vapor deposition. Our study demonstrates that the quality of the In(0.2)Ga(0.8)N/GaN MQW structure is very sensitive to the offset angle of the vicinal substrate. High-resolution X-ray diffraction analyses demonstrated high-order satellite peaks and clear fringes between them for all MQW structures fabricated, from which the interface roughness (IRN) was estimated. The IRN of the In(0.2)Ga(0.8)N/GaN MQW structure fabricated on 0.2 degrees off sapphire substrate was determined as 1.36% of the quantum well layer period. Besides, reciprocal lattice mapping was employed to examine the strain status of the MQW. The lattice relaxation of the same specimen mentioned above was estimated to be 7.4x10(-5). It is therefore manifested that an In(0.2)Ga(0.8)N/GaN MQW structure with abrupt interfaces and good layer periodicity was grown. From it, a shortest radiative lifetime of 14.2 ns and a lowest fluctuation of 5.6 meV in the emission energy of micro-photoluminescence mapping were achieved. In addition, superior material qualities of the whole film fabricated on 0.2 degrees off substrate were recognized by cross-sectional transmission electron microscopy. Based on the results mentioned above, a high-quality In(0.2)Ga(0.8)N/GaN MQW blue light, emitting diode (LED) has been fabricated on 0.2 degrees off substrate, which demonstrated a strong room-temperature electroluminescence emission at the wavelength of 465 nm and with the full width at half maximum of only 19 nm. The same device also showed an output power of 13.4 mW and an external quantum efficiency of 19.2%. Both these characteristics are improved drastically compared with the devices fabricated on the substrates with other offset angles. Conclusively, the use of an appropriately misoriented sapphire substrate is suggested to be effective for elevating the emission efficiency of In(0.2)Ga(0.8)N/GaN MQW blue LED fabricated thereon.
URI: http://dx.doi.org/10.1149/1.3033401
ISSN: 0013-4651
DOI: 10.1149/1.3033401
Volume: 156
Issue: 2
Begin Page: H129
End Page: H133
Appears in Collections:Articles