Zhifeng Shi, 1 Yuantao Zhang, 1,a) Jinxiang Zhang, 1 Hui Wang, 1 Bin Wu, 1 Xupu Cai, 1 Xijun Cui, 1
Xin Dong, 1 Hongwei Liang, 2 Baolin Zhang, 1,a) Guotong Du 1,2
1 State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and
Engineering, Jilin University, Qianjin Street 2699, Changchun 130012, People’s Republic of
China
2 School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian
116023, People’s Republic of China a) Author to whom correspondence should be addressed. Electronic mail: zhangyt@jlu.edu.cn
, zbl@jlu.edu.cn
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The morphological and crystallinity characterizations of the ZnO nanowall networks were performed by AFM (iCon, Veeko), FE-SEM (Jeol-7500F) and XRD (Rigaku Ultima IV). The PL spectra were recorded at RT using a Zolix Omni-λ 500 monochromator/spectrograph with a continuous wave He-Cd laser (325 nm, 30 mW) as the excitation source. The I V characteristic of the device was measured using a Keithley 4200 semiconductor characterization analyzer and
EL spectra were measured by using a home-made acquisition equipment including photomultiplier tube and lock-in amplifier systems.
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FIG. S1. (a) RT PL spectra of the ZnO nanowall networks and p-GaN epitaxial layer. (b) Widerange XRD 2
θ
scans of the ZnO nanowall networks/p-GaN structure. The inset shows the enlarged views of the ZnO(002)/GaN(002) region.
The normalized PL spectra of the epitaxial n-ZnO nanowall networks and that of the p-GaN layer at RT are shown in Figure S1(a), where all of the positions of the emission peak had been calibrated by the laser line (He-Cd laser of 325 nm). The GaN spectrum is characterized by a blue emission band centered at 437 nm, which can be attributed to the radiative transition from the conduction band or unidentified shallow donors to the Mg acceptor levels that was generally
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observed in Mg-doped GaN films due to the deep Mg-related complexes.
1 The unintentionally doped n-type ZnO nanowall networks exhibited an intense near-band-edge (NBE) emission centered at 378 nm associated with the recombination of free excitons. Besides, a relatively low intensity deep-level emission (DLE) band at around 497 nm was observed in the visible region, which mainly originated from the oxygen vacancy related defects existed in ZnO. It can be well accepted that the PL emission characteristics of ZnO films are strongly dependent on both the crystal quality and the microstructure of the films. In view of a rather high PL intensity ratio
(10.56) of the ultraviolet (UV) emission to visible emission, the fabricated ZnO nanowall networks can be regarded as a suitable optical material for LEDs application due to its low concentration of defects in the nanomaterial. So large PL intensity ratio of 10.56 was superior to other results of ZnO nanowall networks synthesized by carbothermal reduction and thermal chemical vapor deposition methods with the help of Au catalyst.
2,3 It was understandable because of the rather high synthesis temperature, as well as the use of catalyst and additive in those studies, the PL performance of these nanowall networks would be inevitably degraded to some extent.
In addition, XRD measurements were performed to examine the structural properties of the
ZnO nanowall networks. As shown in Figure S1(b), the wide-range XRD 2 θ patterns were dominated by the diffraction peaks form ZnO (002) and GaN (002) planes, and no other peaks were detected excepted for the phases from the Al
2
O
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substrate. The two distinct contributors
(inset of Figure S1(b)), with their positions at 34.448 and 34.553°, originated from the (002) planes of ZnO and GaN, respectively. The full width at half-maximum (FWHM) of the (002) peaks of ZnO and GaN are 0.045 and 0.038°, respectively, which is typical of a high-quality heterojunction.
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