Elsevier

Journal of Crystal Growth

Volume 312, Issue 24, 1 December 2010, Pages 3588-3591
Journal of Crystal Growth

Synchrotron X-ray diffraction studies of heteroepitaxial ZnO films grown by pulsed laser deposition

https://doi.org/10.1016/j.jcrysgro.2010.09.034Get rights and content

Abstract

Heteroepitaxial ZnO films were grown by pulsed laser deposition on various substrates such as GaN-buffered C-Al2O3, C-Al2O3, A-Al2O3, and R-Al2O3. The epitaxy nature of the films was investigated mainly by synchrotron X-ray diffraction. The results showed that the GaN interlayer plays a positive role in growing an unstrained, well-aligned epitaxial ZnO film on the basal plane of Al2O3. Importantly, the ZnO film grown on R-Al2O3 has two differently aligned domains. The dominant (1 1 0) oriented domain has much better alignment in the in-plane direction than the minor portion of (0 0 1) oriented domain, while in the out-of-plane direction the two domains have almost the same mosaic distribution.

Introduction

In the past ten years, research on zinc oxide (ZnO) has been rapidly expanding. The availability of high-quality large bulk single crystals and the strong luminescence have led many researchers to pay attention to ZnO. Especially, the high electron mobility, high thermal conductivity, wide and direct band gap, and large exciton binding energy at room temperature make ZnO promising for a wide range of devices that are operated especially in the blue and ultraviolet region [1], [2].

Single crystals in the form of thin films and a high degree of purity are required for advanced applications of ZnO. Several groups have investigated the growth of ZnO films, and the progress in improving quality and purity is significant. Obtaining high-quality single crystalline ZnO films is particularly important for optoelectronic devices, in which the performance is highly sensitive to the crystalline quality of the films. Most epitaxial ZnO films have been grown on single crystal substrates including sapphire [3], [4], [5], GaAs [6], [7], [8], CaF2 [9], [10], [11], ScAlMgO4 [12], [13], and GaN [14], [15], [16].

Many efforts have already been made to grow high-quality ZnO films with low defect densities and to characterize their structural properties [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20]. However, in order to speed up the practical application of ZnO films to optoelectronic devices, studies regarding the nature of heteroepitaxial ZnO films are still necessary.

In this work, we present the results of synchrotron X-ray diffraction (SXRD) study on heteroepitaxial ZnO films grown on C-Al2O3, A-Al2O3, R-Al2O3, and GaN-buffered C-Al2O3 substrates by pulsed laser deposition (PLD). The purpose of this study is to understand details of the substrate effects on the epitaxy nature of ZnO thin films.

Section snippets

Experimental details

Heteroeptaxial ZnO films were grown by PLD on various substrates including C-Al2O3, A-Al2O3, R-Al2O3, and GaN-buffered C-Al2O3. Here, C-, A-, and R-Al2O3 indicate the (0 0 1), (1 1 0), and (0 1 2) Al2O3 substrates, respectively. They are the most widely used substrate types in Al2O3 single crystals. The substrates were ultrasonically cleaned in acetone, methanol, isopropyl alcohol, and deionized water sequentially, before being loaded into a processing chamber. The chamber was evacuated to a vacuum

Results and discussion

According to the in-house θ–2θ XRD results that are not presented here to avoid repetition, only (0 0 l) peaks were observed without any other peaks for the ZnO films grown on GaN-buffered C-Al2O3, C-Al2O3, and A-Al2O3 substrates. In the case of ZnO on R-Al2O3, the (0 0 l) peak was relatively weak and the (1 1 0) peak was strong. First, to investigate the strain state of the films more precisely, the fine θ–2θ scans in SXRD were performed by varying the scattering vector QZ along the substrate

Conclusion

ZnO thin films were heteroepitaxially grown on various substrates including GaN-buffered C-Al2O3, C-Al2O3, A-Al2O3, and R-Al2O3 by pulsed laser deposition. The structural properties of the films were investigated mainly using SXRD. The film on GaN-buffered C-Al2O3 showed no strains and the narrowest mosaic distribution, indicating that the GaN interlayer plays a positive role in growing an unstrained, well-aligned heteroepitaxial ZnO film on C-Al2O3. Different from the case of films on C-Al2O3

Acknowledgments

This work was supported by a grant from the Fundamental R&D Program for Core Technology of Materials funded by the Ministry of Knowledge Economy, Republic of Korea.

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Cited by (2)

  • Blue emission of ZnO nanoporous arrays membrane prepared by novel catalysis-free vertical pulsed-laser ablation

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    Citation Excerpt :

    Recently, two-dimensional (2D) nanostructured ZnO ordered porous arrays, have attracted considerable attention owing to their unique properties and potential applications in microeletronic, optoelectronic and biomedical devices for catalysis, ultrafiltration and biomineralization [8]. Usually, ZnO films have been prepared by modern film technologies, such as magnetron sputtering [9], molecular beam epitaxy [10], metallorganic chemical vapor deposition [11], spray pyrolysis [12], sol–gel [13], electrodeposition [14] and pulsed-laser deposition (PLD) methods [15]. Since PLD can grow films at atomic rate level, which is difficult under normal conditions, it is wildly applied to the fabrication of the metal oxides thin films and related materials.

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