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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.


AFM and micro-Raman images for UV-LEDs grown on (a, c) FS-GaN and (b, d) sapphire substrates.
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Fig2: AFM and micro-Raman images for UV-LEDs grown on (a, c) FS-GaN and (b, d) sapphire substrates.

Mentions: Figure 2 shows the AFM images for the UV-LEDs grown on FS-GaN and sapphire substrates. The root mean square (RMS) of UV-LEDs on sapphire was about 3.1 nm, as shown in Figure 2b. It can be seen that the RMS was decreased to 2.5 nm as the FS-GaN was used, as shown in Figure 2a. Besides, the uniform, well-defined, and long crystallographic steps can be observed on the top surface of UV-LEDs on FS-GaN, suggesting that the UV-LEDs based on InGaN/AlInGaN MQWs of excellent quality are grown. On the other hand, Figure 2c,d displays the micro-Raman mapping images of specimens, within a scanning area of 10 μm × 10 μm. In general, the Raman spectra show two Raman shift peaks: one can be attributed to the E2 (high) mode of the GaN epilayer and another can be attributed to the A1 (LO) mode of the GaN epilayer. Therefore, the average Raman shift peak of E2 (high) for the UV-LEDs grown on FS-GaN and sapphire substrates was located at around 567.8 and 570.4 cm-1, respectively. We can calculate the average strain value of specimen by Equation 1 [10]:Figure 2


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)

AFM and micro-Raman images for UV-LEDs grown on (a, c) FS-GaN and (b, d) sapphire substrates.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig2: AFM and micro-Raman images for UV-LEDs grown on (a, c) FS-GaN and (b, d) sapphire substrates.
Mentions: Figure 2 shows the AFM images for the UV-LEDs grown on FS-GaN and sapphire substrates. The root mean square (RMS) of UV-LEDs on sapphire was about 3.1 nm, as shown in Figure 2b. It can be seen that the RMS was decreased to 2.5 nm as the FS-GaN was used, as shown in Figure 2a. Besides, the uniform, well-defined, and long crystallographic steps can be observed on the top surface of UV-LEDs on FS-GaN, suggesting that the UV-LEDs based on InGaN/AlInGaN MQWs of excellent quality are grown. On the other hand, Figure 2c,d displays the micro-Raman mapping images of specimens, within a scanning area of 10 μm × 10 μm. In general, the Raman spectra show two Raman shift peaks: one can be attributed to the E2 (high) mode of the GaN epilayer and another can be attributed to the A1 (LO) mode of the GaN epilayer. Therefore, the average Raman shift peak of E2 (high) for the UV-LEDs grown on FS-GaN and sapphire substrates was located at around 567.8 and 570.4 cm-1, respectively. We can calculate the average strain value of specimen by Equation 1 [10]:Figure 2

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.