Growth of ZnO nanorods on graphite substrate and its application for Schottky diode
Introduction
ZnO nanorods (NRs) have received much attention due to their direct wide band gap of 3.37 eV, high exciton binding energy of 60 meV, and large piezoelectric coefficient [1], [2]. In particular, a preferred directional growth along the c-direction of the wurtzite crystal structure enables the ZnO crystals to be a promising constituent of various novel device applications, such as transistors, sensors, and piezoelectric, thermoelectric, electrochemical and optoelectronic devices [1], [2]. The fabrication of ZnO NRs has been demonstrated on a variety of substrates including metals, semiconductors, insulators, and polymers [1], [2], [3], [4]. Recently, accompanying with active research on the heterostructures between graphene and semiconductors [5], [6], graphite also has received much attention as a potential substrate for the growth of semiconductors owing to its excellent mechanical and chemical stability, and high thermal and electrical conductivity [7]. Furthermore, graphite has a potential advantage for transferable substrate since it consists of a multi-layer system with nearly decoupled two dimensional (2-D) graphene planes [8]. There are some reports about the deposition of ZnO nanostructures on graphite substrate by the vapor phase method [9], electrochemical deposition [10], and hydrothermal growth combined with the thin film deposition method [11]. However, there are only a few investigations reporting the growth of ZnO NRs on graphite substrate by the all-solution-process method, especially using the hydrothermal method, even though this method has many advantages including a low temperature process which make it applicable to the integration and in situ fabrication of various devices [12], [13]. For a compatible application of ZnO NRs to other devices, all-solution process method at a low temperature on graphite substrate should be possible, and its performance could be compared with conventional substrate, silicon (Si). In this paper, we report on the growth of ZnO NRs on graphite substrate, and on comparative study of the growth of ZnO NRs on Si substrate by using the all-solution process two-step hydrothermal method.
Section snippets
Experimental
The ZnO NRs were grown on highly-oriented pyrolytic graphite and p-type Si (1 0 0) substrates using an all-solution process two-step hydrothermal method involving the formation of a ZnO seed and main ZnO NR layers. Prior to growth, the substrates were rinsed sequentially in acetone, ethanol, and deionized (DI) water to remove contamination. A seed layer for the ZnO NRs was formed by dipping both substrates into 40 mM zinc acetate dihydrate [Zn(CH3COO)2⋅2H2O] dissolved in ethanol solution, followed
Results and discussion
Fig. 1 shows FE-SEM images of the ZnO NRs grown on the p-type Si (1 0 0) and graphite substrates. Without the seed layer, no deposit was observed on both substrates, even for a longer growth time. This indicates that the seed layer plays a critical role in the growth of ZnO NRs on the substrates. The diameter of the ZnO NRs on Si and graphite substrates are 70 nm and 50 nm, respectively. The diameter of the ZnO NRs grown on graphite substrate was slightly smaller than those on Si substrate. And the
Conclusion
In conclusion, we compared the properties of ZnO NRs on graphite and Si substrates grown by using a two-step hydrothermal method. Structural investigations using FE-SEM and XRD showed no significant differences in the morphologies and crystalline quality. Optical investigations using PL measurements showed that the ZnO NRs on graphite contained more lattice point defects than on Si substrate. The I–V characteristics for both samples showed typical rectification properties, exhibiting successful
Acknowledgements
The authors thank Mr. Jae-Min Park (Yeungnam University) for assistance with the experiments. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (2012R1A1A1001711) and by DGIST (13-EN-03).
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