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Growth of Heteroepitaxial ZnO Thin Films on GaN‐Buffered Al 2 O 3 (0001) Substrates by Low‐Temperature Hydrothermal Synthesis at 90 °C
Author(s) -
Kim J. H.,
Kim E.M.,
Andeen D.,
Thomson D.,
DenBaars S. P.,
Lange F. F.
Publication year - 2007
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.200600103
Subject(s) - materials science , wurtzite crystal structure , photoluminescence , crystallite , thin film , band gap , spectroscopy , analytical chemistry (journal) , scanning electron microscope , epitaxy , zinc , optoelectronics , nanotechnology , layer (electronics) , composite material , chemistry , chromatography , quantum mechanics , physics , metallurgy
Heteroepitaxial ZnO films are successfully grown on nondoped GaN‐buffered Al 2 O 3 (0001) substrates in water at 90 °C using a two‐step process. In the first step, a discontinuous ZnO thin film (ca. 200 nm in thickness) consisting of hexagonal ZnO crystallites is grown in a solution containing Zn(NO 3 )·6 H 2 O and NH 4 NO 3 at ca. pH 7.5 for 24 h. In the second step, a dense and continuous ZnO film (ca. 2.5 μm) is grown on the first ZnO thin film in a solution containing Zn(NO 3 )·6 H 2 O and sodium citrate at ca. pH 10.9 for 8 h. Scanning electron microscopy, X‐ray diffraction, UV‐vis absorption spectroscopy, photoluminescence spectroscopy, and Hall‐effect measurement are used to investigate the structural, optical, and electrical properties of the ZnO films. X‐ray diffraction analysis shows that ZnO is a monocrystalline wurtzite structure with an epitaxial orientation relationship of (0001)[11 $ \bar 2 $ 0] ZnO ∥(0001)[11 $ \bar 2 $ 0] GaN . Optical transmission spectroscopy of the two‐step grown ZnO film shows a bandgap energy of 3.26 eV at room temperature. A room‐temperature photoluminescence spectrum of the ZnO film reveals only a main peak at ca. 380 nm without any significant defect‐related deep‐level emissions. The electrical property of ZnO film showed n‐type behavior with a carrier concentration of 3.5 × 10 18 cm –3 and a mobility of 10.3 cm 2 V –1 s –1 .