@article{4137ae315a4a49a8a677a5338e8aa20f,
title = "Surface stoichiometry and activity control for atomically smooth low dislocation density ZnO and pseudomorphic MgZnO epitaxy on a Zn-polar ZnO substrate by the helicon-wave-excited-plasma sputtering epitaxy method",
abstract = "The helicon-wave-excited-plasma sputtering (HWPS) method was exemplified to be one of the versatile epitaxial growth techniques for the fabrication of low dislocation density semiconductor epilayers and heterostructures exhibiting atomically smooth surface morphology. For a case study, ZnO homoepitaxy and Mgx Zn1-x O (x=0.08,0.19) heteroepitaxy on a Zn-polar ZnO substrate were carried out. According to the surface damage-free property, high temperature growth with appropriate stoichiometry control enabled the growth of ZnO homoepitaxial layers exhibiting a smooth surface morphology with 0.26 nm high monolayer atomic steps. Their tilt and twist mosaics reflecting the threading dislocation densities having screw and edge components were comparable to those of the substrate, being under the resolution limit (18 arcsec). The surface morphology and crystal mosaicity of pseudomorphic Mgx Zn 1-x O (x0.19) epilayers were quite similar to those of the ZnO underlayer. The luminescence spectra of the ZnO and Mgx Zn 1-x O epilayers at 293 K exhibited a predominant near-band-edge emission and negligible broad emission bands due to deep levels. The results indicate that the growth mode of the HWPS method resembles that of molecular beam epitaxy methods.",
author = "Y. Sawai and K. Hazu and Chichibu, {S. F.}",
note = "Funding Information: The authors would like to thank Dr. K. Nakahara and Dr. S. Akasaka of ROHM Co. Ltd. for SIMS measurements and Dr. M. Sumiya of National Institute for Materials Science for the CAICISS analysis. They also thank H. Amaike and Dr. T. Onuma for help in the experiments. This work was supported in part by Grant-in Aids of Scientific Research under Grant Nos. 19360137 and 22246037 under MEXT and CANTech, IMRAM, Tohoku University, Japan. FIG. 1. Representative XRCs taken for the (a) ( 10 1 ¯ 2 ) and (b) (0002) reflections of Zn-polar ZnO and Mg x Zn 1 − x O ( x = 0.08 , 0.19 ) epilayers grown by HWPSE. For comparison, the data for an as-received Zn-polar ZnO substrate are also shown. FIG. 2. (a) The AFM image map for the ZnO epilayers as functions of T g and f ( O 2 ) . The AFM image of an as-received Zn-polar ZnO substrate is also shown. (b) rms roughness value of the ZnO epilayers as functions of f ( O 2 ) and T g . (c) rms roughness value and growth rate of the ZnO epilayers as a function of f ( O 2 ) . T g was 950 ° C . The abbreviation “NS” means nearly-stoichiometric. FIG. 3. (a) PL spectra at 293 K of the Zn-polar ZnO epilayers grown at 950 ° C . For comparison, PL spectrum of the substrate is also shown. (b) TRPL signals at 293 K for the NBE emission of the Zn-polar ZnO epilayers grown under different conditions. (c) Room-temperature PL lifetimes ( τ PL ) and FWHM values for the NBE emission peak, and the intensity ratio of the NBE peak to the deep emission band ( I NBE / I DL ) at 293 K for the ZnO epilayers grown at 950 ° C plotted as a function of f ( O 2 ) . FIG. 4. (a) The x-ray RSM images taken at the ( 11 2 ¯ 4 ) reflections of the 0.7 μ m thick Mg x Zn 1 − x O ( x = 0.08 , 0.19 ) / 0.3 μ m thick ZnO structures grown on a Zn-polar ZnO substrate. (b) The lattice parameters a and c of the ZnO and Mg x Zn 1 − x O ( x = 0.08 , 0.19 ) epilayers obtained from the RSM images. FIG. 5. The AFM images and cross-sectional height profiles for (a) the ZnO underlayer, (b) Mg 0.08 Zn 0.92 O , and (c) Mg 0.19 Zn 0.81 O epilayers. (d) A schematic planview of a bilayer on a wurtzite structure. FIG. 6. (a) The AFM images of the 0.7 μ m thick Mg 0.19 Zn 0.81 O epilayers grown at 980 ° C on the Zn-polar ZnO base layer as a function of f ( O 2 ) . (b) The surface rms roughness and the growth rate of Mg x Zn 1 − x O ( x = 0.08 , 0.19 ) epilayers as a function of f ( O 2 ) . T g was 980 ° C . FIG. 7. The PL spectra for the best ZnO and Mg 0.08 Zn 0.92 O epilayers and the CL spectrum of the Mg 0.19 Zn 0.81 O epilayer measured at 293 K. The inset shows the emission peak energy as a function of MgO molar fraction x . ",
year = "2010",
month = sep,
day = "15",
doi = "10.1063/1.3485600",
language = "English",
volume = "108",
journal = "Journal of Applied Physics",
issn = "0021-8979",
publisher = "American Institute of Physics",
number = "6",
}