1. SSL Lab. SSL Lab. Solid State Lighting Lab. Southern Taiwan University 1 Adviser : Hon Kuan Adviser : Hon Kuan Wen-Cheng Tzou Wen-Cheng Tzou Reporter : Bo-Jun Liu Southern Taiwan University Effect of an electron blocking layer on the piezoelectric field in InGaN/GaN multiple quantum well light-emitting diodes

2. SSL Lab. SSL Lab. Solid State Lighting Lab. Southern Taiwan University 2 Outline Introduction Experiments Result and Discussion Conclusion References

3. SSL Lab. SSL Lab. Solid State Lighting Lab. Southern Taiwan University 3 Introduction The effect of an electron blocking layer (EBL) on the piezoelectric field in InGaN/GaN multiple quantum well (MQW). Electric-field-dependent ER measurements showed an enhanced piezoelectric field in LEDs with a p-AlGaN EBL compared with LEDs without EBL.

4. SSL Lab. SSL Lab. Solid State Lighting Lab. Southern Taiwan University Experiments 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. 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. 4

5. SSL Lab. SSL Lab. Solid State Lighting Lab. Southern Taiwan University 5 Result and Discussion FIG. 1. (Color online) EL spectra with increasing current for (a) LED A without an EBL and (b) LED B with a p-AlGaN EBL.

6. SSL Lab. SSL Lab. Solid State Lighting Lab. Southern Taiwan University 6 Result and Discussion (c) the variations of FWHM, and (d) EL peak energies as a function of current.

7. SSL Lab. SSL Lab. Solid State Lighting Lab. Southern Taiwan University 7 Result and Discussion FIG. 2. (Color online) (a) Reverse-bias dependent ER spectra and (b) peak energies and intensities of ER spectra with reverse-bias voltages for LED A without an EBL and LED B with a p-AlGaN EBL.

8. SSL Lab. SSL Lab. Solid State Lighting Lab. Southern Taiwan University 8 Result and Discussion FIG. 3. (Color online) Time-resolved PL spectra at selected time for (a) LED A without an EBL and (b) LED B with a p-AlGaN EBL.

9. SSL Lab. SSL Lab. Solid State Lighting Lab. Southern Taiwan University 9 Conclusion investigated the effect of a p-AlGaN EBL on the piezoelectric field in InGaN/GaN MQW LEDs. In contrast with the LEDs without a p-AlGaN EBL, 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 current densities. Furthermore, based on the QCSE model, the residual strain is estimated and it is used for our x-ray kinetic simulation. Our simulation considering the strain relaxation agrees well with the measured XRD patterns.

10. SSL Lab. SSL Lab. Solid State Lighting Lab. Southern Taiwan University 10 References Nakamura, Science 281, 956 (1998). E. F. Schubert and J. K. Kim, Science 308, 1274 (2005). T. Mukai, M. Yamada, and S. Nakamura, Jpn. J. Appl. Phys., 38(Part 1), 3976 (1999). E. 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). M. H. Kim, M. F. Schubert, Q. Dai, J. K. Kim, E. F. Schubert, J. Piprek, and Y. Park, Appl. Phys. Lett. 91, 183507 (2007). Y.-K. Kuo, M.-C. Tsai, and S.-H. Yen, Opt. Commun. 282, 4252 (2009). S.-H. Park and S.-L. Chuang, Appl. Phys. Lett. 72, 3103 (1998). T. M. Hsu, C. Y. Lai, W.-H. Chang, C.-C. Pan, C.-C. Chuo, and J.-I. Chyi, Appl. Phys. Lett. 84, 1114 (2004). F. 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. G. Franssen, P. Perlin, and T. Suski, Phys. Rev. B 69, 045310 (2004). H. S. Kim, J. Y. Lin, H. X. Jiang, W. W. Chow, A. Botchkarev, and H. Morkoc, Appl. Phys. Lett. 73, 3426 (1998).

11. SSL Lab. SSL Lab. Solid State Lighting Lab. Southern Taiwan University 11 T hanks for your attention !