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Engineering the carrier dynamics of InGaN nanowire white light-emitting diodes by distributed p-AlGaN electron blocking layers.

Nguyen HP, Djavid M, Woo SY, Liu X, Connie AT, Sadaf S, Wang Q, Botton GA, Shih I, Mi Z - Sci Rep (2015)

Bottom Line: As such, nonradiative surface recombination, that dominates the carrier dynamics of conventional axial nanowire LED structures, can be largely eliminated, leading to significantly increased carrier lifetime from ~0.3 ns to 4.5 ns.Moreover, the p-doped AlGaN barrier layers can function as distributed electron blocking layers (EBLs), which is found to be more effective in reducing electron overflow, compared to the conventional AlGaN EBL.An output power of >5 mW is measured for a 1 mm × 1 mm device, which is more than 500 times stronger than the conventional InGaN axial nanowire LEDs without AlGaN distributed EBLs.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Electrical and Computer Engineering, McGill University, 3480 University Street, Montreal, Quebec H3A 0E9, Canada [2] Department of Electrical and Computer Engineering, New Jersey Institute of Technology, University Heights, Newark, New Jersey 07102.

ABSTRACT
We report on the demonstration of a new type of axial nanowire LED heterostructures, with the use of self-organized InGaN/AlGaN dot-in-a-wire core-shell nanowire arrays. The large bandgap AlGaN shell is spontaneously formed on the sidewall of the nanowire during the growth of AlGaN barrier of the quantum dot active region. As such, nonradiative surface recombination, that dominates the carrier dynamics of conventional axial nanowire LED structures, can be largely eliminated, leading to significantly increased carrier lifetime from ~0.3 ns to 4.5 ns. The luminescence emission is also enhanced by orders of magnitude. Moreover, the p-doped AlGaN barrier layers can function as distributed electron blocking layers (EBLs), which is found to be more effective in reducing electron overflow, compared to the conventional AlGaN EBL. The device displays strong white-light emission, with a color rendering index of ~95. An output power of >5 mW is measured for a 1 mm × 1 mm device, which is more than 500 times stronger than the conventional InGaN axial nanowire LEDs without AlGaN distributed EBLs.

No MeSH data available.


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(a, b) STEM-HAADF images of the InGaN/AlGaN dot-in-a-wire core-shell heterostructures showing the InGaN dots, AlGaN barriers, and the Al-rich core-shell by atomic-number contrast. The acquisition area of the EELS spectrum image is boxed in green in (b). (c) Elemental mapping from EELS spectrum imaging of the green area marked in (b) of the group III elements extracted from the In M4,5, Ga L2,3, and Al L2,3-edges. (d) Higher magnification atomic-resolution HAADF image of the selected region (boxed in red dashed line) in (b) showing the AlGaN core-shell and barriers in detail.
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f2: (a, b) STEM-HAADF images of the InGaN/AlGaN dot-in-a-wire core-shell heterostructures showing the InGaN dots, AlGaN barriers, and the Al-rich core-shell by atomic-number contrast. The acquisition area of the EELS spectrum image is boxed in green in (b). (c) Elemental mapping from EELS spectrum imaging of the green area marked in (b) of the group III elements extracted from the In M4,5, Ga L2,3, and Al L2,3-edges. (d) Higher magnification atomic-resolution HAADF image of the selected region (boxed in red dashed line) in (b) showing the AlGaN core-shell and barriers in detail.

Mentions: High-angle annular dark-field (HAADF) atomic-number contrast imaging of single nanowires is shown in Figures 2(a) and (b), presenting clearly the ten InGaN/AlGaN quantum dots in the GaN nanowire. A detailed view of the active region in Figure 2(b) shows that the ten InGaN dots (bright contrast) are centrally confined and capped by the AlGaN barriers (dark contrast), each of which form an Al-rich core-shell at the nanowire sidewall. Elemental analysis was performed using electron energy-loss spectroscopy (EELS) in scanning transmission electron microscope (STEM) on the nanowire in Figure 2(b). Elemental maps from spectrum imaging in Figure 2(c) illustrate the distribution variation of group III elements in the different regions. The In-map extracted from the In M4,5-edge shows a strong localization in only the quantum dots. The Ga-map shows a signal maximum towards the center of the nanowire because of the increased projected thickness, as well as an overall deficiency in the active region and at the sidewalls in the presence of In or Al alloying elements. Most notable is the Al distribution in the AlGaN barrier layers and the Al-rich core-shell in the Al-map extracted with the Al L2,3-edge. The Al-rich core-shell is continuous from each of the AlGaN barriers and is present throughout the whole active region and propagates well into the n-GaN segment (also visible in Figure 2(a)). A higher magnification HAADF image of the core-shell in the orientation (Figure 2(d)) also shows the continuity of the core-shell from the AlGaN barriers, suggesting their formation during the growth of the AlGaN barriers from the strong lateral diffusion of Al-rich AlGaN. The overall high crystalline quality of the dot-in-a-wire core-shell heterostructures is demonstrated in the atomic-resolution images of Figures 2(b) and (d).


Engineering the carrier dynamics of InGaN nanowire white light-emitting diodes by distributed p-AlGaN electron blocking layers.

Nguyen HP, Djavid M, Woo SY, Liu X, Connie AT, Sadaf S, Wang Q, Botton GA, Shih I, Mi Z - Sci Rep (2015)

(a, b) STEM-HAADF images of the InGaN/AlGaN dot-in-a-wire core-shell heterostructures showing the InGaN dots, AlGaN barriers, and the Al-rich core-shell by atomic-number contrast. The acquisition area of the EELS spectrum image is boxed in green in (b). (c) Elemental mapping from EELS spectrum imaging of the green area marked in (b) of the group III elements extracted from the In M4,5, Ga L2,3, and Al L2,3-edges. (d) Higher magnification atomic-resolution HAADF image of the selected region (boxed in red dashed line) in (b) showing the AlGaN core-shell and barriers in detail.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4296300&req=5

f2: (a, b) STEM-HAADF images of the InGaN/AlGaN dot-in-a-wire core-shell heterostructures showing the InGaN dots, AlGaN barriers, and the Al-rich core-shell by atomic-number contrast. The acquisition area of the EELS spectrum image is boxed in green in (b). (c) Elemental mapping from EELS spectrum imaging of the green area marked in (b) of the group III elements extracted from the In M4,5, Ga L2,3, and Al L2,3-edges. (d) Higher magnification atomic-resolution HAADF image of the selected region (boxed in red dashed line) in (b) showing the AlGaN core-shell and barriers in detail.
Mentions: High-angle annular dark-field (HAADF) atomic-number contrast imaging of single nanowires is shown in Figures 2(a) and (b), presenting clearly the ten InGaN/AlGaN quantum dots in the GaN nanowire. A detailed view of the active region in Figure 2(b) shows that the ten InGaN dots (bright contrast) are centrally confined and capped by the AlGaN barriers (dark contrast), each of which form an Al-rich core-shell at the nanowire sidewall. Elemental analysis was performed using electron energy-loss spectroscopy (EELS) in scanning transmission electron microscope (STEM) on the nanowire in Figure 2(b). Elemental maps from spectrum imaging in Figure 2(c) illustrate the distribution variation of group III elements in the different regions. The In-map extracted from the In M4,5-edge shows a strong localization in only the quantum dots. The Ga-map shows a signal maximum towards the center of the nanowire because of the increased projected thickness, as well as an overall deficiency in the active region and at the sidewalls in the presence of In or Al alloying elements. Most notable is the Al distribution in the AlGaN barrier layers and the Al-rich core-shell in the Al-map extracted with the Al L2,3-edge. The Al-rich core-shell is continuous from each of the AlGaN barriers and is present throughout the whole active region and propagates well into the n-GaN segment (also visible in Figure 2(a)). A higher magnification HAADF image of the core-shell in the orientation (Figure 2(d)) also shows the continuity of the core-shell from the AlGaN barriers, suggesting their formation during the growth of the AlGaN barriers from the strong lateral diffusion of Al-rich AlGaN. The overall high crystalline quality of the dot-in-a-wire core-shell heterostructures is demonstrated in the atomic-resolution images of Figures 2(b) and (d).

Bottom Line: As such, nonradiative surface recombination, that dominates the carrier dynamics of conventional axial nanowire LED structures, can be largely eliminated, leading to significantly increased carrier lifetime from ~0.3 ns to 4.5 ns.Moreover, the p-doped AlGaN barrier layers can function as distributed electron blocking layers (EBLs), which is found to be more effective in reducing electron overflow, compared to the conventional AlGaN EBL.An output power of >5 mW is measured for a 1 mm × 1 mm device, which is more than 500 times stronger than the conventional InGaN axial nanowire LEDs without AlGaN distributed EBLs.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Electrical and Computer Engineering, McGill University, 3480 University Street, Montreal, Quebec H3A 0E9, Canada [2] Department of Electrical and Computer Engineering, New Jersey Institute of Technology, University Heights, Newark, New Jersey 07102.

ABSTRACT
We report on the demonstration of a new type of axial nanowire LED heterostructures, with the use of self-organized InGaN/AlGaN dot-in-a-wire core-shell nanowire arrays. The large bandgap AlGaN shell is spontaneously formed on the sidewall of the nanowire during the growth of AlGaN barrier of the quantum dot active region. As such, nonradiative surface recombination, that dominates the carrier dynamics of conventional axial nanowire LED structures, can be largely eliminated, leading to significantly increased carrier lifetime from ~0.3 ns to 4.5 ns. The luminescence emission is also enhanced by orders of magnitude. Moreover, the p-doped AlGaN barrier layers can function as distributed electron blocking layers (EBLs), which is found to be more effective in reducing electron overflow, compared to the conventional AlGaN EBL. The device displays strong white-light emission, with a color rendering index of ~95. An output power of >5 mW is measured for a 1 mm × 1 mm device, which is more than 500 times stronger than the conventional InGaN axial nanowire LEDs without AlGaN distributed EBLs.

No MeSH data available.


Related in: MedlinePlus