The presence of NiO buffer layer probably blocks the electron injection from the ZnO to the GaN because STI571 the smaller electron affinity (1.46 eV) and large band gap (3.86 eV) of NiO could

have possibly raised the height of the conduction band barrier. Thus, the recombination of carriers is followed in the ZnO nanorods, and the luminescence is radically increased. Moreover, the insets of Figure 5a,b show the digital photographs of nanorod- and nanotube-based LEDs with a NiO buffer layer. The luminescence properties of the buffer-layer-containing LEDs are strongly enhanced compared to those without NiO buffer layer, ZnO nanorod- and nanotube-based LEDs; this can be attributed to more hole injections and a large number of electron-hole recombination at the interface. Figure 5 EL spectrum of n-ZnO/p-GaN and n-ZnO/NiO/p-GaN.

(a) ZnO nanorods and (b) ZnO nanotubes. Insets show digital photographs of ZnO nanorod- and nanotube-based buy CH5183284 LEDs with NiO buffer layer. Conclusion In this study, n-type ZnO/Ro 61-8048 concentration p-type GaN- and n-type ZnO/NiO/p-type GaN-based white light-emitting diodes are designed using two known morphologies of ZnO including nanorods and nanotubes. ZnO nanorods were well aligned and perpendicular to the GaN substrate, and some of the samples were almost fully chemically etched into nanotubes. XRD study shows the c-axis-oriented growth of the ZnO crystal structure with the possible involvement of GaN at (002) crystal plane. Both the CL and EL intensities were significantly increased by inserting a thin layer of NiO at the interface between

the n-type ZnO and the p-type GaN due to possible blocking of electron injections from the ZnO to the GaN. Using the NiO buffer layer, the confinement is created which helps Phosphoribosylglycinamide formyltransferase in the development of efficient LEDs based on n-type ZnO/NiO/p-type GaN heterojunctions. Acknowledgement We are grateful to the University of Sindh, Pakistan, NED University, Pakistan and Linköping University, Sweden for their financial support. References 1. Chen Y, Bagnall D, Yao T: ZnO as a novel photonic material for the UV region. Mater Sci Eng B 2000, 75:190–198.CrossRef 2. Huang MH, Mao S, Feick H, Yan H, Wu Y, Kind H, Weber E, Russo R, Yang P: Room-temperature ultraviolet nanowire nanolasers. Science 2001, 292:1897–1899.CrossRef 3. Park WI, Jun YH, Jung SW, Yi GC: Excitonic emissions observed in ZnO single crystal nanorods. Appl Phys Lett 2003, 82:964–966.CrossRef 4. Özgür Ü, Alivov YI, Liu C, Teke A, Reshchikov MA, Doan S, Avrutin V, Cho SJ, Morkoç H: A comprehensive review of ZnO materials and devices. J Appl Phys 2005, 98:041301.CrossRef 5. Wang G, Chu S, Zhan N, Lin Y, Chernyak L, Liu J: ZnO homojunction photodiodes based on Sb-doped p-type nanowire array and n-type film for ultraviolet detection. Appl Phys Lett 2011, 98:041107.CrossRef 6. Chen MT, Lu MP, Wu YJ, Song J, Lee CY, Lu MY, Chang YC, Chou LJ, Wang ZL, Chen LJ: Near UV LEDs made with in situ doped p-n homojunction ZnO nanowire arrays.