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The effect of free-standing GaN substrate on carrier localization in ultraviolet InGaN light-emitting diodes.

Tsai MT, Chu CM, Huang CH, Wu YH, Chiu CH, Li ZY, Tu PM, Lee WI, Kuo HC - Nanoscale Res Lett (2014)

Bottom Line: The micro-Raman shift peak mapping image shows low standard deviation (STD), indicating that the UV-LED epi-wafer of low curvature and MQWs of weak quantum-confined Stark effect (QCSE) were grown.Clearly, the FS-GaN can not only improve the light output power but also reduce the efficiency droop phenomenon at high injection current.Based on the results mentioned above, the FS-GaN can offer UV-LEDs based on InGaN/AlInGaN MQW structures with benefits, such as high crystal quality and small carrier localization degree, compared with the UV-LEDs on sapphire.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrophysics, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu, 30010, Taiwan, allen_ken@hotmail.com.

ABSTRACT
In this study, we have grown 380-nm ultraviolet light-emitting diodes (UV-LEDs) based on InGaN/AlInGaN multiple quantum well (MQW) structures on free-standing GaN (FS-GaN) substrate by atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD), and investigated the relationship between carrier localization degree and FS-GaN. The micro-Raman shift peak mapping image shows low standard deviation (STD), indicating that the UV-LED epi-wafer of low curvature and MQWs of weak quantum-confined Stark effect (QCSE) were grown. High-resolution X-ray diffraction (HRXRD) analyses demonstrated high-order satellite peaks and clear fringes between them for the UV-LEDs grown on the FS-GaN substrate, from which the interface roughness (IRN) was estimated. The temperature-dependent photoluminescence (PL) measurement confirmed that the UV-LEDs grown on the FS-GaN substrate exhibited better carrier confinement. Besides, the high-resolution transmission electron microscopy (HRTEM) and energy-dispersive spectrometer (EDS) mapping images verified that the UV-LEDs on FS-GaN have fairly uniform distribution of indium and more ordered InGaN/AlInGaN MQW structure. Clearly, the FS-GaN can not only improve the light output power but also reduce the efficiency droop phenomenon at high injection current. Based on the results mentioned above, the FS-GaN can offer UV-LEDs based on InGaN/AlInGaN MQW structures with benefits, such as high crystal quality and small carrier localization degree, compared with the UV-LEDs on sapphire.

No MeSH data available.


Forward current and normalized external quantum efficiency. (a) Forward current as a function of light output for the UV-LEDs grown on sapphire and FS-GaN substrates. (b) Normalized external quantum efficiency as a function of forward current for LEDs on sapphire and FS-GaN under CW mode.
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Fig6: Forward current and normalized external quantum efficiency. (a) Forward current as a function of light output for the UV-LEDs grown on sapphire and FS-GaN substrates. (b) Normalized external quantum efficiency as a function of forward current for LEDs on sapphire and FS-GaN under CW mode.

Mentions: Figure 6a shows the typical power-current (L-I) characteristics for both samples. As we can see, the output power of the UV-LEDs grown on the FS-GaN substrate was enhanced by 78% at 20 mA compared with the UV-LEDs grown on the sapphire substrate. Finally, Figure 6b shows the EQE as a function of forward current for the UV-LEDs grown on FS-GaN and sapphire substrates. The EQE of these two types of UV-LEDs are under CW operations. Therefore, the efficiency droop, defined as (ηpeak - η100 mA)/ηpeak, was reduced from 20% in the UV-LEDs grown on the sapphire substrate to 3% in the UV-LEDs grown on the FS-GaN substrate. Clearly, the performance of UV-LEDs on FS-GaN can be expected due to ultra-low dislocation density and high thermal conductivity of FS-GaN. Comparing these measurements, the use of the FS-GaN substrate is not only to improve the crystal quality of UV-LED device but also to reduce the efficiency droop under high injection current.Figure 6


The effect of free-standing GaN substrate on carrier localization in ultraviolet InGaN light-emitting diodes.

Tsai MT, Chu CM, Huang CH, Wu YH, Chiu CH, Li ZY, Tu PM, Lee WI, Kuo HC - Nanoscale Res Lett (2014)

Forward current and normalized external quantum efficiency. (a) Forward current as a function of light output for the UV-LEDs grown on sapphire and FS-GaN substrates. (b) Normalized external quantum efficiency as a function of forward current for LEDs on sapphire and FS-GaN under CW mode.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4494039&req=5

Fig6: Forward current and normalized external quantum efficiency. (a) Forward current as a function of light output for the UV-LEDs grown on sapphire and FS-GaN substrates. (b) Normalized external quantum efficiency as a function of forward current for LEDs on sapphire and FS-GaN under CW mode.
Mentions: Figure 6a shows the typical power-current (L-I) characteristics for both samples. As we can see, the output power of the UV-LEDs grown on the FS-GaN substrate was enhanced by 78% at 20 mA compared with the UV-LEDs grown on the sapphire substrate. Finally, Figure 6b shows the EQE as a function of forward current for the UV-LEDs grown on FS-GaN and sapphire substrates. The EQE of these two types of UV-LEDs are under CW operations. Therefore, the efficiency droop, defined as (ηpeak - η100 mA)/ηpeak, was reduced from 20% in the UV-LEDs grown on the sapphire substrate to 3% in the UV-LEDs grown on the FS-GaN substrate. Clearly, the performance of UV-LEDs on FS-GaN can be expected due to ultra-low dislocation density and high thermal conductivity of FS-GaN. Comparing these measurements, the use of the FS-GaN substrate is not only to improve the crystal quality of UV-LED device but also to reduce the efficiency droop under high injection current.Figure 6

Bottom Line: The micro-Raman shift peak mapping image shows low standard deviation (STD), indicating that the UV-LED epi-wafer of low curvature and MQWs of weak quantum-confined Stark effect (QCSE) were grown.Clearly, the FS-GaN can not only improve the light output power but also reduce the efficiency droop phenomenon at high injection current.Based on the results mentioned above, the FS-GaN can offer UV-LEDs based on InGaN/AlInGaN MQW structures with benefits, such as high crystal quality and small carrier localization degree, compared with the UV-LEDs on sapphire.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrophysics, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu, 30010, Taiwan, allen_ken@hotmail.com.

ABSTRACT
In this study, we have grown 380-nm ultraviolet light-emitting diodes (UV-LEDs) based on InGaN/AlInGaN multiple quantum well (MQW) structures on free-standing GaN (FS-GaN) substrate by atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD), and investigated the relationship between carrier localization degree and FS-GaN. The micro-Raman shift peak mapping image shows low standard deviation (STD), indicating that the UV-LED epi-wafer of low curvature and MQWs of weak quantum-confined Stark effect (QCSE) were grown. High-resolution X-ray diffraction (HRXRD) analyses demonstrated high-order satellite peaks and clear fringes between them for the UV-LEDs grown on the FS-GaN substrate, from which the interface roughness (IRN) was estimated. The temperature-dependent photoluminescence (PL) measurement confirmed that the UV-LEDs grown on the FS-GaN substrate exhibited better carrier confinement. Besides, the high-resolution transmission electron microscopy (HRTEM) and energy-dispersive spectrometer (EDS) mapping images verified that the UV-LEDs on FS-GaN have fairly uniform distribution of indium and more ordered InGaN/AlInGaN MQW structure. Clearly, the FS-GaN can not only improve the light output power but also reduce the efficiency droop phenomenon at high injection current. Based on the results mentioned above, the FS-GaN can offer UV-LEDs based on InGaN/AlInGaN MQW structures with benefits, such as high crystal quality and small carrier localization degree, compared with the UV-LEDs on sapphire.

No MeSH data available.