Structural and photoluminescence properties of GaN/ZnO core‐shell nanowires with their shells sputtered

Abstract

We have reported the preparation of ZnO-coated GaN nanowires and investigated changes in the structural and photoluminescence (PL) properties by the application of a thermal annealing process. For fabricating the core-shell nanowires, Zn target was used to sputter ZnO shell onto GaN core nanowires. X-ray diffraction (XRD) analysis indicated that the annealed core-shell nanowires clearly exhibited the ZnO as well as GaN phase. The transmissoin electron microscopy (TEM) investigation suggested that annealing has induced the crystallization of ZnO shell layer. We have carried out Gaussian deconvolution analysis for the measured PL spectra, revealing that the core GaN nanowires exhibited broad emission which consist of red, yellow, blue, and ultraviolet peaks. ZnO-sputtering induced new peaks in the green region. Thermal annealing reduced the relative intensity of the green emission.

Hybrid density functional study of band alignment in ZnO–GaN and ZnO–(Ga1−xZnx)(N1−xOx)–GaN heterostructures

“…1,2 The slight lattice mismatch (B1.86%) between wurtzite (w-) ZnO and GaN and the type-II band alignment of the two crystals has motivated intensive studies on ZnO-GaN heterostructures, because type-II band alignment is always accompanied by natural charge separation which is advantageous for promising solar energy harvesting, such as water splitting, dye-sensitized and even regular solar cells. [3][4][5] The synthesis of ZnO-GaN core-shell heterostructured nanowires (h-NWs) and nanotubes (h-NTs) has been reported, [6][7][8] and the GaN (core)-ZnO (shell) h-NTs were found to have absorption spectra in the visible light region (1.9-3.6 eV). 7,8 Based on first-principles calculation and an effective mass model, we predicted that ZnO (core)-GaN (shell) h-NWs rather than GaN (core)-ZnO (shell) ones exhibit natural charge spatial separation behavior in our previous work.…”

“…[3][4][5] The synthesis of ZnO-GaN core-shell heterostructured nanowires (h-NWs) and nanotubes (h-NTs) has been reported, [6][7][8] and the GaN (core)-ZnO (shell) h-NTs were found to have absorption spectra in the visible light region (1.9-3.6 eV). 7,8 Based on first-principles calculation and an effective mass model, we predicted that ZnO (core)-GaN (shell) h-NWs rather than GaN (core)-ZnO (shell) ones exhibit natural charge spatial separation behavior in our previous work. 9 Thanks to the unique geometry of core-shell h-NWs which have a GaN/ZnO interface extending along the axial direction and carrier separation taking place in the axial direction of the h-NWs, photo-generated carriers can reach the interface with high efficiency without substantial bulk recombination, which improves carrier collection and overall efficiency with respect to comparable axially-modulated h-NWs.…”

Geometry‐Induced Dislocations in Coaxial Heterostructural Nanotubes

“…The ZnO core structure was chosen as a template for GaN because of the same crystallographic structures and their similar lattice constants. Additionally, ZnO/GaN core‐shell structures of n‐type ZnO and p‐type GaN are ideal for optoelectronic devices 26–28. Interestingly, in this nanostructure, misfit dislocations are localized in specific areas and in specific directions, as shown in transmission electron microscope (TEM) images (Figures 1b,c).…”

Natural charge spatial separation and quantum confinement of ZnO/GaN-core/shell nanowires

“…[13][14][15] The synthesis of ZnO/GaN core/shell NWs and nanotubes with type-II band alignment have been reported. [16][17][18] The spectrum of GaN-core/ZnO-shell nanotubes exhibit band energies from 1.9 eV to 3.6 eV, which are in the visible region. 17,18 Theoretical study of GaN/ZnO super-lattice and random-alloy has provided important insights and guidelines for designing band gap reduction.…”

“…[16][17][18] The spectrum of GaN-core/ZnO-shell nanotubes exhibit band energies from 1.9 eV to 3.6 eV, which are in the visible region. 17,18 Theoretical study of GaN/ZnO super-lattice and random-alloy has provided important insights and guidelines for designing band gap reduction. 19 However, the band offset and build-in electric filed at the interface of ZnO/GaN core/shell NWs have never been reported.…”