Influence of Si-Doping on the Characteristics ofInGaN–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

Outline

• Introduction

• Experiment

• Results and discussion

• Conclusion

• References

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.

MQW InGaN/GaN ： 3nm/10nm five periodes@770ºC (Barrier doping Si 3×1017cm-3)

Sapphire

GaN nucleation layer (30nm) @ 560ºC

n-GaN@ 1060ºC

Experiment

Mg doped Al0.1Ga0.9N@1060ºC

p-GaN

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.

Results and discussion

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

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.

Results and discussion

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

Results and discussion

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

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.

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.

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)

Outline

• Introduction

• Experiment

• Results and discussion

• Conclusion

• References

Introduction

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

MQW Al0.07Ga0.93N/GaN ： 3nm/7nm five periodes@770ºC (Barrier doping Si 3×1018 to 3×1018cm-3)

Sapphire

LT buffer layer

GaN(1µm)@ 1100ºC

Experiment

Mg doped A0.1Ga0.9N@1060ºCp-GaN

Results and discussion

Fig. 1. AFM surface images for Al0.07Ga0.93N/GaN 5QW. Si concentration in barrier layer was (a) undoped, (b) 6×1018 cm-3,(c) 4.2×1019 cm-3, and (d) 9×1019 cm-3.

undoped 6 ×1018cm-3

4.2×1019cm-3 9×1019cm-3

Results and discussion

Fig. 2. Across-sectiona l TEM image for Al0.07Ga0.93N/GaN 5QW. Si concentration in barrier layer was 9×1019 cm-3.

Results and discussion

Fig. 3. Relationship between the size of the V-shaped defects and Si concentration.

1

4

2

56

3

Results and discussion

Fig. 4. AFM surface images for Al0.07Ga0.93N layer (a) and GaN layer (b) with Si concentration of 4×1019 cm-3

Al0.07Ga0.93N

barrier

Results and discussion

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

Conclusion

• PL intensity gradually increases with Si doping. But when the Si concentration exceeds 4.2 × 1019 cm-3, PL intensity was rapidly decreased with the formation of V shaped defect.

Efficiency droop behaviors of InGaN/GaN multiple-quantum-well light-emitting diodes with varying

quantum well thicknessY.-L. Li, Y.-R. Huang, and Y.-H. Lai

APPLIED PHYSICS LETTERS 91, 181113 2007

Outline

• Introduction

• Experiment

• Results and discussion

• Conclusion

• References

Introduction

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

Experiment

Chips 350 ×350µm2

FIG. 1. Color online Schematic structure InGaN/GaN multiple-quantumwellLEDs with varied well thicknesses.

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.

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.

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.

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/cm2.

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。

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 ofInGaN–GaN Multiple Quantum-Well Blue LightEmitting 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 .

• Thanks for your attention !