The effect of Mg0.1Zn0.9O layer thickness on optical band gap of ZnO/Mg0.1Zn0.9O nano-scale multilayer thin films prepared by pulsed laser deposition method

Abstract Epitaxial ZnO/Mg0.1Zn0.9O (MZO) nano-scale multilayer thin films were prepared on Al2O3 (0001) substrates by pulsed laser deposition. The ZnO/MZO multilayer thin films were grown by stacking alternate layers of ZnO and Mg0.1Zn0.9O with a laser fluence, repetition rate, substrate temperature and oxygen partial pressure of 3 J/cm2, 5 Hz, 600 °C and 3.8 × 10− 7 Pa, respectively. The thickness of an individual ZnO layer was maintained at 3 nm, whereas that of the MZO layers was varied from 3 nm to 15 nm. Cross-sectional transmission electron microscopy revealed alternating layers of bright and dark contrast, indicating the formation of a ZnO/MZO multilayer. X-ray diffraction results showed that multilayer thin films were epitaxially grown as a hexagonal wurzite phase with orientation relationship of ( 0001 ) [ 10 1 ¯ 1 ] multilayer | | ( 0001 ) [ 10 1 ¯ 1 ] substrate . The 2θ value of the (0002) peak of the ZnO/MZO multilayer thin films increased from 34.30° to 34.71°, indicating that Mg is replaced with Zn in the hexagonal lattice in the MZO of ZnO/MZO multilayer. UV–visible spectroscopy showed a systematic increase in the band gap of the ZnO/MZO multilayer thin films from 3.34 eV to 3.70 eV with increasing MZO layer thickness, which suggests that the band gap energy of a ZnO/MZO multilayer thin film can be controlled by varying the thickness of each constituent layer.

[1]  Hongen Shen,et al.  Ultraviolet photoconductive detector based on epitaxial Mg0.34Zn0.66O thin films , 2001 .

[2]  Duan Zhao,et al.  Effect of interface on luminescence properties in ZnO/MgZnO heterostructures , 2006 .

[3]  M. Okuyama,et al.  Strained SrTiO3/BaTiO3 Superlattices Formed by Laser Ablation Technique and Their High Dielectric Properties , 1995 .

[4]  R. D. Shannon.  Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides , 1976 .

[5]  N. Binh,et al.  Enhanced second-harmonic generation in Mg0.05Zn0.95O/Mg0.4Zn0.6O multilayers , 2005 .

[6]  Akira Ohtomo,et al.  MgxZn1−xO as a II–VI widegap semiconductor alloy , 1998 .

[7]  P. Bhattacharya,et al.  Comparative study of Mg doped ZnO and multilayer ZnO/MgO thin films , 2004 .

[8]  Ichiro Takeuchi,et al.  Compositionally-tuned epitaxial cubic MgxZn1−xO on Si(100) for deep ultraviolet photodetectors , 2003 .

[9]  Seonuk Park,et al.  Schottky nanocontacts on ZnO nanorod arrays , 2003 .

[10]  D. C. Reynolds,et al.  Optically pumped ultraviolet lasing from ZnO , 1996 .

[11]  Novel cubic ZnxMg1−xO epitaxial heterostructures on Si (100) substrates , 2001 .

[12]  Noritaka Usami,et al.  Growth of ZnO∕MgZnO quantum wells on sapphire substrates and observation of the two-dimensional confinement effect , 2005 .

[13]  D. Shen,et al.  Temperature dependence of carrier transfer and exciton localization in ZnO/MgZnO heterostructure , 2006 .

[14]  C. Liu,et al.  Second-harmonic generation in MgxZn1−xO/MgyZn1−yO multilayers fabricated by metalorganic chemical vapor deposition , 2005 .

[15]  K. Sreenivas,et al.  Structural and optical properties of magnetron sputtered MgxZn1−xO thin films , 2006 .

[16]  J. Moon,et al.  Integration of artificial SrTiO3/BaTiO3 superlattices on Si substrates using a TiN buffer layer by pulsed laser deposition method , 2006 .

[17]  Masataka Inoue,et al.  Growth of ZnO/Zn1−xMgxO films by pulsed laser ablation , 2005 .

[18]  H. Koinuma,et al.  High-throughput optical characterization for the development of a ZnO-based ultraviolet semiconductor-laser , 2002 .

[19]  T. Venkatesan,et al.  Realization of band gap above 5.0 eV in metastable cubic-phase MgxZn1−xO alloy films , 2002 .

[20]  Shu-Shen Li,et al.  The electronic structure of strained ZnO/MgxZn1-xOZnO/MgxZn1-xO superlattices and the influence of polarization , 2009 .

[21]  S. Fujita,et al.  MBE growth of wide band gap wurtzite MgZnO quasi-alloys with MgO/ZnO superlattices for deep ultraviolet optical functions , 2005 .