1. Influence of Si-Doping on the Characteristics of InGaN–GaN Multiple Quantum-Well Blue Light Emitting Diodes Sum DJ L. W. Wu, S. J. Chang, T. C. Wen, Y. K. Su, Senior Member, IEEE, J. F. Chen, Member, IEEE, W. C. Lai, C. H. Kuo, C. H. Chen, and J. K. Sheu IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 38, NO. 5, MAY 2002

2. Outline Introduction Experiment Results and discussion Conclusion References

3. Introduction Low temperature will significantly degrade the crystal quality of the GaN barrier layers. Such a problem can be overcome by introducing Si doping in the GaN layers.

4. MQW InGaN/GaN ： 3nm/10nm five periodes @770ºC (Barrier doping Si 3×10 17 cm -3 ) Sapphire GaN nucleation layer (30nm) @ 560ºC n-GaN@ 1060ºC Experiment Mg doped Al 0.1 Ga 0.9 N@1060ºC p-GaN

5. Results and discussion Fig. 1. Typical room-temperature photoluminescence spectra of the MQW blue LED structure with an unintentionally doped or Si-doped barrier. The photoluminescence peak wavelength of the Si-doped barrier LED does not reveal significant blue shift due to Coulomb screening of the internal electric field.

6. Results and discussion Fig. 2. X-ray diffraction spectra of unintentionally doped or Si-doped barrier MQW LED.

7. Results and discussion Fig. 3. Typical I–V characteristics of forward bias for unintentionally doped and Si-doped barrier LED. The forward voltage for the unintentionally doped and Si-doped barrier LED is 4.52 and 3.5 V at 20-mA injection current.

8. Results and discussion Fig. 4. Dynamic resistance depends on the applied voltage for the unintentionally doped and Si-doped barrier LED at forward operation.

9. Results and discussion Fig. 5. Dominated wavelength of electroluminescence spectra depends on the injection current for the unintentionaly doped and Si-doped barrier LED.

10. Results and discussion Fig. 6. Dlectroluminescence spectra of the unintentionally doped barrier and Si-doped barrier LED at forward dc currents of 20 mA. The luminous intensity at forward dc currents of 20 mA for the unintentionally doped barrier LED is 25.1 mcd. For the LED with the Si-doped barrier, the luminous intensity is 36.1 mcd.

11. Conclusion Compared with unintentionally doped samples, double crystal X-ray diffraction (DCXRD) indicates that Si-doping in the barrier layers can improve the crystal and interfacial qualities of the InGaN–GaN MQW LEDs.

12. Structural analysis of Si-doped AlGaN/GaN multi-quantum wells Tetsuya Nakamura, Shingo Mochizuki, Shinji Terao, Tomoaki Sano, Motoaki Iwaya, Satoshi Kamiyama, Hiroshi Amanob,c, Isamu Akasaki Journal of Crystal Growth 237–239 1129–1132(2002)

13. Outline Introduction Experiment Results and discussion Conclusion References

14. Introduction It was reported that Si doping improves the optical properties of AlGaN/GaN MQW and GaInN/GaN MQW.

15. MQW Al 0.07 Ga 0.93 N/GaN ： 3nm/7nm five periodes @770ºC (Barrier doping Si 3×10 18 to 3×10 18 cm -3 ) Sapphire LT buffer layer GaN(1µm)@ 1100ºC Experiment Mg doped A 0.1 Ga 0.9 N@1060ºC p-GaN

16. Results and discussion Fig. 1. AFM surface images for Al 0.07 Ga 0.93 N/GaN 5QW. Si concentration in barrier layer was (a) undoped, (b) 6×10 18 cm -3,(c) 4.2×10 19 cm -3, and (d) 9×10 19 cm -3. undoped6 ×10 18 cm -3 4.2×10 19 cm -3 9×10 19 cm -3

17. Results and discussion Fig. 2. Across-sectiona l TEM image for Al 0.07 Ga 0.93 N/GaN 5QW. Si concentration in barrier layer was 9×10 19 cm -3.

18. Results and discussion Fig. 3. Relationship between the size of the V-shaped defects and Si concentration. 1 4 2 5 6 3

19. Results and discussion Fig. 4. AFM surface images for Al 0.07 Ga 0.93 N layer (a) and GaN layer (b) with Si concentration of 4×10 19 cm -3 Al 0.07 Ga 0.93 N barrier

20. Results and discussion Fig. 5. PL maximum intensity and surface covering ratio of Vshaped defects as a function of Si concentration.

21. Conclusion PL intensity gradually increases with Si doping. But when the Si concentration exceeds 4.2 × 10 19 cm -3, PL intensity was rapidly decreased with the formation of V shaped defect.

22. Efficiency droop behaviors of InGaN/GaN multiple- quantum-well light-emitting diodes with varying quantum well thickness Y.-L. Li, Y.-R. Huang, and Y.-H. Lai APPLIED PHYSICS LETTERS 91, 181113 2007

23. Outline Introduction Experiment Results and discussion Conclusion References

24. Introduction Well-known fundamental problem needs to be overcome, namely, the efficiency “droop,” which is the reduction in efficiency as the current is increased.

25. Experiment Chips 350 ×350µm 2 FIG. 1. Color online Schematic structure InGaN/GaN multiple-quantumwell LEDs with varied well thicknesses.

26. Results and discussion FIG. 2. Color online Temperaturevaried from 10 to 300 K photoluminescence measurements for roomtemperature IQE assessment of InGaN/GaN MQW LEDs with varied well thicknesses.

27. Results and discussion FIG. 3. Color online Roomtemperature EL spectra of MQW LEDs with varied well thicknesses under various injection currents. The peaks of the emission spectra shift toward shorter wavelengths blueshift as the current is increased from 10 to 250 mA, as indicated by the two vertical lines.

28. Results and discussion FIG. 4. Color online Normalized external quantum efficiency measurements of the MQW LEDs with varied well thicknesses. Measurements are pulsed with 5% duty cycle. For samples with different well thicknesses, the efficiency drop from the highest value at low current density to 200 A/cm2 is 2.7%, 17.9%, 36.7%, and 40.4%, respectively. This figure clearly illustrates a reduced efficiency-droop effect for thicker quantum wells.

29. Conclusion We have demonstrated that the droop effect can be drastically reduced to less than 5% at a current density as high as 200 A/cm 2.

30. 整理 在 barrier 摻 si 能介由 Coulomb screening 減緩 QCSE 使得電子電洞波函數較為 重疊，但摻雜過多會影響磊晶品質。 減少 well 的厚度能使得電子電洞波函 數較為重疊，但過窄的 well 會突顯局 限能力不足的現象。 barrier 摻 si 會使得 V-shaped defects 有面 積變小、深度變深的效應。

31. References L. W. Wu, S. J. Chang, T. C. Wen, Y. K. Su, Senior Member, IEEE, J. F. Chen, Member, IEEE, W. C. Lai, C. H. Kuo,C. H. Chen, and J. K. Sheu“Influence of Si-Doping on the Characteristics of InGaN–GaN Multiple Quantum-Well Blue Light Emitting Diodes” IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 38, NO. 5, MAY 2002. Tetsuya Nakamura, Shingo Mochizuki, Shinji Terao, Tomoaki Sano, Motoaki Iwaya, Satoshi Kamiyama, Hiroshi Amanob,c, Isamu Akasaki“Structural analysis of Si-doped AlGaN/GaN multi-quantum wells ” Journal of Crystal Growth 237–239 1129– 1132(2002). Y.-L. Li, Y.-R. Huang, and Y.-H. Lai“Efficiency droop behaviors of InGaN/GaN multiple-quantum-well light-emitting diodes with varying quantum well thickness ” APPLIED PHYSICS LETTERS 91, 181113 2007.

32. Thanks for your attention !