1. Dong-Yul Lee, Sang-Heon Han,a) Dong-Ju Lee, Jeong Wook Lee, Dong-Joon Kim, Young Sun Kim, and Sung-Tae Kim Samsung LED Co. Ltd., Suwon 443-743, South Korea (Received 7 October 2011; accepted 12 January 2012; published online 27 January 2012) ©2012 American Institute of Physics. Effect of an electron blocking layer on the piezoelectric field in InGaN/GaN multiple quantum well light-emitting diodes Adviser ： Hon Kuan Reporter ： Bo-Jun Liu

2. Outline Introduction Experiments Result and Discussion Conclusion References 2

3. Introduction Recently, significant progress in the performance of InGaN-based light- emitting diodes (LEDs) has enabled more applications such as backlight units, automotive headlights, and general illumination. As demand for brighter and more efficient LEDs increases, the problem of efficiency droop with increasing current in LEDs becomes most important, especially for high-power applications. The effect of an electron blocking layer (EBL) on the piezoelectric field in InGaN/GaN multiple quantum well (MQW). 3

4. Experimental Method GaN 2 μ m Sapphire n-GaN 3 μ m MQW InGaN/GaN (5-pair)(well 3nm/barrier 12nm) p-GaN 150nm LED A 4 InGaN/GaN MQW LEDs were grown on a (0001) patterned sapphire substrate using metal organic chemical vapor deposition. The structures of the LEDs consisted of 2.0 lm thick undoped GaN, 3.0-lm thick Si-doped n-GaN, and 5 pairs of InGaN/GaN (3.0 nm/12 nm) MQW. For LED A, a 150 nm-thick Mg-doped p-GaN contact layer was grown directly on the MQW without a p-AlGaN EBL.

5. Experimental Method GaN 2 μ m Sapphire n-GaN 3 μ m MQW InGaN/GaN (5-pair)(well 3nm/barrier 12nm) p-Al 0.22 Ga 0.78 N EBL 40nm p-GaN 150nm LED B 5 For LED B, a 40 nm thick Mg-doped p-Al0.22Ga0.78N EBL was grown on the MQW, followed by a 110 nm thick Mg-doped p-GaN contact layer.

6. Results and Discussion FIG. (a). LED A without an EBL. 6

7. Results and Discussion FIG. (b). LED B with a p-AlGaN EBL. 7

8. Results and Discussion FIG. (c) the variations of FWHM. 8

9. Results and Discussion FIG. (d). EL peak energies as a function of current. 9

10. Conclusion The LEDs with a p-AlGaN EBL exhibited reduced blueshift and a sublinear increase of full width at half maximum in their EL spectra at low cThese behaviors can be explained by the strong localization of injected carriers in dominant InGaN regions due to an increased piezoelectric field in the InGaN well layer by the subsequent growing EBL current densities. 10

11. Reference 1S. Nakamura, Science 281, 956 (1998). 2E. F. Schubert and J. K. Kim, Science 308, 1274 (2005). 3T. Mukai, M. Yamada, and S. Nakamura, Jpn. J. Appl. Phys., 38(Part 1), 3976 (1999). 4E. F. Schubert, Light-Emitting Diodes (Cambridge University Press, Cambridge, 2003). 5S.-H. Han, D.-Y. Lee, S.-J. Lee, C.-Y. Cho, M.-K. Kwon, S. P. Lee, D. Y. Noh, D.-J. Kim, Y. C. Kim, and S.-J. Park, Appl. Phys. Lett. 94, 231123 (2009). 6M. H. Kim, M. F. Schubert, Q. Dai, J. K. Kim, E. F. Schubert, J. Piprek, and Y. Park, Appl. Phys. Lett. 91, 183507 (2007). 7Y.-K. Kuo, M.-C. Tsai, and S.-H. Yen, Opt. Commun. 282, 4252 (2009). 8S.-H. Park and S.-L. Chuang, Appl. Phys. Lett. 72, 3103 (1998). 9T. M. Hsu, C. Y. Lai, W.-H. Chang, C.-C. Pan, C.-C. Chuo, and J.-I. Chyi, Appl. Phys. Lett. 84, 1114 (2004). 10F. H. Pollak, “Modulation Spectroscopy of Semiconductors and Semiconductor Microstructures,” in Handbook on Semiconductors, edited by T. S. Moss (Elsevier, Amsterdam, 1994), Vol. 2, pp. 527–635. 11G. Franssen, P. Perlin, and T. Suski, Phys. Rev. B 69, 045310 (2004). 12H. S. Kim, J. Y. Lin, H. X. Jiang, W. W. Chow, A. Botchkarev, and H. Morkoc, Appl. Phys. Lett. 73, 3426 (1998). 11

12. Thanks for your attention !

13. 補充資料 - 極化 自發極化是由於晶體沿著 wurtzite 結構之 [0001] 方向成長時，單位晶胞內正負電荷中 心不重合，形成偶極矩，而在無外加電場 作用下自然存在的極化現象 壓電極化則是因為在長晶過程中，磊晶層 與基板晶格不匹配，因此在層與層間的電 荷受到晶格形變所產生之作用力而累積在 接面處

14. 補充資料 - 偶極 電偶極矩是一個向量，其方向由負電荷指 向正電荷。 電偶極 p=qd 。 q 為一個電偶極的電荷大小， d 則為其間距。

15. 補充資料 - 極化計算 ( 自發極化 )

17. 總極化與電荷密度計算

18. 電荷密度示意圖

19. 伸張應力壓縮應力