ZHAO Peng-cheng, ZHANG Zhen-zhong, YAO Bin etc. Smooth Surface Morphology of ZnO Thin Films on Sapphire at Low Temperature[J]. Chinese Journal of Luminescence, 2014,35(5): 542-547
ZHAO Peng-cheng, ZHANG Zhen-zhong, YAO Bin etc. Smooth Surface Morphology of ZnO Thin Films on Sapphire at Low Temperature[J]. Chinese Journal of Luminescence, 2014,35(5): 542-547 DOI: 10.3788/fgxb20143505.0542.
Smooth Surface Morphology of ZnO Thin Films on Sapphire at Low Temperature
ZnO thin film that grows at low temperature benefits the sharp interface in heterostructure and enough doping level of acceptor in ZnO. In general
the smooth growth can be easily obtained at temperature higher than 600 ℃
but difficult in the case of low growth temperature. In this work
by controlling the growth ambient and growth rate
a series of ZnO thin films with smooth surface were grown on
a
-plane sapphire substrates at 450 ℃ by the plasma-assisted molecular beam epitaxy (P-MBE). The growth was performed in oxygen-rich atmosphere. To tune the growth rate
the zinc flux was changed by varying the K-cell temperature of zinc source (
T
k
) while keeping oxygen flux constant. The growth rate of the samples is only 40~100 nm/h. Scanning electron microscopy (SEM) images indicate that there are lots of irregular grains on the thin film surface at high zinc flux
and most of the grains disappear gradually from the surface with the zinc flux decreasing. This smooth growth with low growth rate is conducive to control finely the layer thickness and smoothness in the multilayer structure. The root mean square (RMS) surface roughness is only 0.238 nm
measured by atomic force microscopy (AFM). The smooth surface benefits from the low growth rate and small sub-lattice mismatch between the
c
-plane-ZnO thin film and
a
-plane-sapphire substrate.
关键词
Keywords
references
Look D C. Recent advances in ZnO materials and devices[J].Mater. Sci. Eng. B, 2001, 80(1-3):383-387.[2] Ozgur U, Alivov Y I, Liu C, et al. A comprehensive review of ZnO materials and devices[J].J. Appl. Phys., 2005, 98(4):041301-1-3.[3] Osinsky A, Dong J W, Chernyak L, et al. MgZnO/AlGaN heterostructure light-emitting diodes[J].Appl. Phys. Lett., 2004, 85(19):4272-4274.[4] Pauporte T, Lincot D, Pelle F, et al. Toward laser emission of epitaxial nanorod arrays of ZnO grown by electrodeposition[J].Appl. Phys. Lett., 2006, 89(23):233112-1-3.[5] Tsukazaki A, Ohtomo A, Kawasaki M, et al. Repeated temperature modulation epitaxy for p-type doping and light-emitting diode based on ZnO[J].Nat. Mater., 2005, 4(1):42-46.[6] Kawasaki M. A key for realizing p-type ZnO[C]//Pacific Rim Conference on Lasers and Electro-Optics, Tokyo: IEEE, 2005:464-465.[7] Ko H J, Chen Y F, Hong S K, et al. MBE growth of high-quality ZnO films on epi-GaN[J].J. Cryst. Growth, 2000, 209(4):816-821.[8] Ohtomo A, Tamura K, Saikusa K, et al. Single crystalline ZnO films grown on lattice-matched ScAlMgO4(0001) substrates[J].Appl. Phys. Lett., 1999, 75(17):2635-2637.[9] Tsukazaki A, Ohtomo A, Yoshida S, et al. Layer-by-layer growth of high-optical-quality ZnO film on atomically smooth and lattice relaxed ZnO buffer layer[J].Appl. Phys. Lett., 2003, 83(14):2784-2786.[10] Kato H, Sano M, Miyamoto K, et al. High-quality ZnO epilayers grown on Zn-face ZnO substrates by plasma-assisted molecular beam epitaxy[J].J. Cryst. Growth, 2004, 265(3-4):375-381.[11] Kato H, Sano M, Miyamoto K, et al. High-quality ZnO epilayers grown on Zn-polar ZnO substrates by plasma-assisted molecular beam epitaxy[J].Phys. Stat. Sol. B, 2004, 241(3):612-615.[12] Fons P, Iwata K, Niki S, et al. Uniaxial locked growth of high-quality epitaxial ZnO films on (1120) α-Al2O3[J].J. Cryst. Growth, 2000, 209(2-3):532-536.[13] Jiao S J, Zhang Z Z, Lu Y M, et al. ZnO p-n junction light-emitting diodes fabricated on sapphire substrates[J].Appl. Phys. Lett., 2006, 88(3):031911-1-3.[14] Wei Z P, Lu Y M, Shen D Z, et al. Room temperature p-n ZnO blue-violet light-emitting diodes[J].Appl. Phys. Lett., 2007, 90(4):042113-1-3.[15] Chen Y F, Bagnall D M, Koh H J, et al. Plasma assisted molecular beam epitaxy of ZnO on c-plane sapphire: Growth and characterization[J].J. Appl. Phys., 1998, 84(7):3912-3918.[16] Fons P, Iwata K, Yamada A, et al. Uniaxial locked epitaxy of ZnO on the a face of sapphire[J].Appl. Phys. Lett., 2000, 77(12):1801-1803.[17] Kato H, Sano M, Miyamoto K, et al. MBE growth of Zn-polar ZnO on MOCVD-ZnO templates[J].Phys. Stat. Sol. (b), 2004, 241(12):2825-2829.[18] Sawai Y, Hazu K, Chichibu S F. 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[J].J. Appl. Phys., 2010, 108(6):063541-1-8.[19] Setiawan A, Ko H J, Hong S K, et al. Study on MgO buffer in ZnO layers grown by plasma-assisted molecular beam epitaxy on Al2O3(0001)[J].Thin Solid Films, 2003, 445(2):213-218.[20] Park J S, Hong S K, Im I H, et al. Growth of high-quality ZnO films on Al2O3 (0001) by plasma-assisted molecular beam epitaxy[J].J. Cryst. Growth, 2009, 311(7):2163-2166.[21] Fons P, Iwata K, Niki S, et al. Growth of high-quality epitaxial ZnO films on α-Al2O3[J].J. Cryst. Growth, 1999, 201-202:627-632.[22] Iwata K, Fons P, Niki S, et al. Improvement of electrical properties in ZnO thin films grown by radical source(RS)-MBE[J].Phys. Stat. Sol. A, 2000, 180(1):287-292.[23] Chen Y F, Ko H J, Hong S K, et al. Morphology evolution of ZnO(0001) surface during plasma-assisted molecular-beam epitaxy[J].Appl. Phys. Lett., 2002, 80(8):1358-1360.[24] Kato H, Sano M, Miyamoto K, et al. Effect of O/Zn flux ratio on crystalline quality of ZnO films grown by plasma-assisted molecular beam epitaxy[J].Jpn. J. Appl. Phys., 2003, 42(4B):2241-2244.[25] Eaglesham D J, Cerullo M. Dislocation-free Stranski-Krastanow growth of Ge on Si(100)[J].Phy. Rev. Lett., 1990, 64(16):1943-1946.[26] Cordier Y, Ferre D, Chauveau J M, et al. Surface morphology and strain relaxation of InAlAs buffer layers grown lattice mismatched on GaAs with inverse steps[J].Appl. Sur. Sci., 2000, 166(1-4):442-445.[27] Pal R, Singh M, Murlidharan R, et al. Lattice mismatch and surface morphology studies on InxGa1-xAs epilayers grown on GaAs substrates[J].Bull. Mater. Sci., 1998, 21(4):313-316.[28] Baxter J B, Aydil E S. Epitaxial growth of ZnO nanowires on a-and c-plane sapphire[J].J. Cryst. Growth, 2005, 274(3-4):407-411.