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Electroluminescence of ordered ZnO nanorod array/p-GaN light-emitting diodes with graphene current spreading layer.

Dong JJ, Hao HY, Xing J, Fan ZJ, Zhang ZL - Nanoscale Res Lett (2014)

Bottom Line: Ordered ZnO nanorod array/p-GaN heterojunction light-emitting diodes (LEDs) have been fabricated by introducing graphene as the current spreading layer, which exhibit improved electroluminescence performance by comparison to the LED using a conventional structure (indium-tin-oxide as the current spreading layer).In addition, by adjusting the diameter of ZnO nanorod array in use, the light emission of the ZnO nanorod array/p-GaN heterojunction LEDs was enhanced further.This work has great potential applications in solid-state lighting, high performance optoelectronic devices, and so on. 78.60.Fi; 85.60.Jb; 78.67.Lt; 81.10.Dn.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Science, China University of Geosciences (Beijing), 29 Xue Yuan Road, Haidian District, Beijing, 100083, China.

ABSTRACT

Unlabelled: Ordered ZnO nanorod array/p-GaN heterojunction light-emitting diodes (LEDs) have been fabricated by introducing graphene as the current spreading layer, which exhibit improved electroluminescence performance by comparison to the LED using a conventional structure (indium-tin-oxide as the current spreading layer). In addition, by adjusting the diameter of ZnO nanorod array in use, the light emission of the ZnO nanorod array/p-GaN heterojunction LEDs was enhanced further. This work has great potential applications in solid-state lighting, high performance optoelectronic devices, and so on.

Pacs: 78.60.Fi; 85.60.Jb; 78.67.Lt; 81.10.Dn.

No MeSH data available.


Ordered and aligned ZnO nanorod arrays on the p-GaN substrates grown at 50°C for 6 h. With the reactant concentration of (a) 0.05 M and (b) 0.035 M by using 500 nm PS microspheres without RIE; (c) 0.05 M and (d) 0.035 M by RIE of 500 nm PS microspheres for 1.5 min.
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Figure 1: Ordered and aligned ZnO nanorod arrays on the p-GaN substrates grown at 50°C for 6 h. With the reactant concentration of (a) 0.05 M and (b) 0.035 M by using 500 nm PS microspheres without RIE; (c) 0.05 M and (d) 0.035 M by RIE of 500 nm PS microspheres for 1.5 min.

Mentions: EL emission of the ZnO nanorod array-based LED can be enhanced further by choosing an optimal diameter of the ZnO nanorods, as stated earlier. It has been demonstrated in our previous work that the diameter of ZnO nanorods can be tuned by either varying the solution concentration during hydrothermal growth or RIE of PS microspheres [6,12]. As shown in Figure 1, ordered and aligned ZnO nanorod arrays on the p-GaN substrates were grown at 50°C for 6 h, and the diameter was reduced from 380 nm (Figure 1a) to 300 nm (Figure 1b) by varying the solution concentration from 0.05 to 0.035 M, and 220 nm (Figure 1c) by RIE of PS microspheres for 1.5 min. Here, the diameter of the PS microspheres in use is 500 nm. Taking advantage of both two measures mentioned above, ZnO nanorod array with a diameter of 170 nm was obtained, as shown in Figure 1d. It can be seen that all the ZnO nanorod arrays reserve hexagonal periodicity and evenly distribution inheriting from the PS microsphere SAM, and the spacing between two neighboring nanorods is 500 nm which is predefined by the diameter of the PS microspheres. All of the ZnO nanorod arrays are hexagonal faceted perfectly aligned normal to the underlying substrate, indicating that each ZnO nanorod is a single crystal of wurtzite ZnO with growth direction along [0001]. Besides, the hexagonal nanorods are well oriented with their side faces parallel to each other, demonstrating the perfect epitaxial growth of ZnO nanorods on the GaN substrate, which has been confirmed by the X-ray diffraction (XRD) measurements in our previous report [12].The highly ordered ZnO nanorod arrays on the p-GaN substrate were then used to construct LED devices with graphene as the current spreading layer, and the schematic structure of the device is illustrated in Figure 2a. To confirm the complete unfolding of the graphene layer on the top of ZnO nanorod array, a typical SEM image of ZnO nanorod array covered with graphene is shown in Figure 2b, and the corresponding SEM image without graphene is given in the inset of Figure 2b for comparison. It can be seen that both of the ZnO nanorod arrays are hexagonal faceted with a smooth surface and a clear edge, indicating a tight contact between graphene and ZnO nanorods. In addition, for the small defects of the ZnO nanorod array, as indicated by the arrows in Figure 2b, the graphene layer plays an important role in modifying the gap. Obviously, a continuous graphene film was covered on the top of separated ZnO nanorods and plays a role of current spreading as an interconnecting material of ZnO nanorods, so under forward current injection, each ZnO nanorod acts as a light emitter.


Electroluminescence of ordered ZnO nanorod array/p-GaN light-emitting diodes with graphene current spreading layer.

Dong JJ, Hao HY, Xing J, Fan ZJ, Zhang ZL - Nanoscale Res Lett (2014)

Ordered and aligned ZnO nanorod arrays on the p-GaN substrates grown at 50°C for 6 h. With the reactant concentration of (a) 0.05 M and (b) 0.035 M by using 500 nm PS microspheres without RIE; (c) 0.05 M and (d) 0.035 M by RIE of 500 nm PS microspheres for 1.5 min.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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Figure 1: Ordered and aligned ZnO nanorod arrays on the p-GaN substrates grown at 50°C for 6 h. With the reactant concentration of (a) 0.05 M and (b) 0.035 M by using 500 nm PS microspheres without RIE; (c) 0.05 M and (d) 0.035 M by RIE of 500 nm PS microspheres for 1.5 min.
Mentions: EL emission of the ZnO nanorod array-based LED can be enhanced further by choosing an optimal diameter of the ZnO nanorods, as stated earlier. It has been demonstrated in our previous work that the diameter of ZnO nanorods can be tuned by either varying the solution concentration during hydrothermal growth or RIE of PS microspheres [6,12]. As shown in Figure 1, ordered and aligned ZnO nanorod arrays on the p-GaN substrates were grown at 50°C for 6 h, and the diameter was reduced from 380 nm (Figure 1a) to 300 nm (Figure 1b) by varying the solution concentration from 0.05 to 0.035 M, and 220 nm (Figure 1c) by RIE of PS microspheres for 1.5 min. Here, the diameter of the PS microspheres in use is 500 nm. Taking advantage of both two measures mentioned above, ZnO nanorod array with a diameter of 170 nm was obtained, as shown in Figure 1d. It can be seen that all the ZnO nanorod arrays reserve hexagonal periodicity and evenly distribution inheriting from the PS microsphere SAM, and the spacing between two neighboring nanorods is 500 nm which is predefined by the diameter of the PS microspheres. All of the ZnO nanorod arrays are hexagonal faceted perfectly aligned normal to the underlying substrate, indicating that each ZnO nanorod is a single crystal of wurtzite ZnO with growth direction along [0001]. Besides, the hexagonal nanorods are well oriented with their side faces parallel to each other, demonstrating the perfect epitaxial growth of ZnO nanorods on the GaN substrate, which has been confirmed by the X-ray diffraction (XRD) measurements in our previous report [12].The highly ordered ZnO nanorod arrays on the p-GaN substrate were then used to construct LED devices with graphene as the current spreading layer, and the schematic structure of the device is illustrated in Figure 2a. To confirm the complete unfolding of the graphene layer on the top of ZnO nanorod array, a typical SEM image of ZnO nanorod array covered with graphene is shown in Figure 2b, and the corresponding SEM image without graphene is given in the inset of Figure 2b for comparison. It can be seen that both of the ZnO nanorod arrays are hexagonal faceted with a smooth surface and a clear edge, indicating a tight contact between graphene and ZnO nanorods. In addition, for the small defects of the ZnO nanorod array, as indicated by the arrows in Figure 2b, the graphene layer plays an important role in modifying the gap. Obviously, a continuous graphene film was covered on the top of separated ZnO nanorods and plays a role of current spreading as an interconnecting material of ZnO nanorods, so under forward current injection, each ZnO nanorod acts as a light emitter.

Bottom Line: Ordered ZnO nanorod array/p-GaN heterojunction light-emitting diodes (LEDs) have been fabricated by introducing graphene as the current spreading layer, which exhibit improved electroluminescence performance by comparison to the LED using a conventional structure (indium-tin-oxide as the current spreading layer).In addition, by adjusting the diameter of ZnO nanorod array in use, the light emission of the ZnO nanorod array/p-GaN heterojunction LEDs was enhanced further.This work has great potential applications in solid-state lighting, high performance optoelectronic devices, and so on. 78.60.Fi; 85.60.Jb; 78.67.Lt; 81.10.Dn.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Science, China University of Geosciences (Beijing), 29 Xue Yuan Road, Haidian District, Beijing, 100083, China.

ABSTRACT

Unlabelled: Ordered ZnO nanorod array/p-GaN heterojunction light-emitting diodes (LEDs) have been fabricated by introducing graphene as the current spreading layer, which exhibit improved electroluminescence performance by comparison to the LED using a conventional structure (indium-tin-oxide as the current spreading layer). In addition, by adjusting the diameter of ZnO nanorod array in use, the light emission of the ZnO nanorod array/p-GaN heterojunction LEDs was enhanced further. This work has great potential applications in solid-state lighting, high performance optoelectronic devices, and so on.

Pacs: 78.60.Fi; 85.60.Jb; 78.67.Lt; 81.10.Dn.

No MeSH data available.