Epitaxial growth of ZnO films on Si(111)
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In this paper, we report the growth of ZnO films on silicon substrates using a pulsed laser deposition technique. These films were deposited on Si(111) directly as well as by using thin buffer layers of AlN and GaN. All the films were found to have c-axis-preferred orientation aligned with normal to the substrate. Films with AlN and GaN buffer layers were epitaxial with preferred in-plane orientation, while those directly grown on Si(111) were found to have random in-plane orientation. A decrease in the frequency of the E2(2) Raman mode and a red shift of the band-edge photoluminescence peak due to the presence of tensile strain in the film, was observed. Various possible sources for the observed biaxial strain are discussed.
During the last few years wide-band-gap semiconductors have attracted significant scientific and technological interest.1–3 ZnO holds a special position in materials physics due to its interesting electrical and optical characteristics.1,2 Because of its higher exciton binding energy (60 meV) and higher luminescent efficiencies it is considered a substitute for GaN of the III–V semiconductor family3 for various optical and light emitting applications. Its band gap (3.28 eV) is quite close to that of GaN (3.44 eV). The band gap of GaN can be increased or decreased by alloying with AlN (6.2 eV) or with InN (1.9 eV). Similarly, ZnO can be alloyed with MgO (8.2 eV) to increase the band gap or with CdO (2.0 eV) to decrease it. For the use of ZnO in light emitting and nonlinear optical applications, high-quality single-crystal ZnO films are required. Epitaxial films of ZnO have been previously grown on (0001) planes of sapphire by the domain epitaxy mechanism.4,5 The growth of highquality ZnO films on silicon is expected to offer additional advantages as it will provide opportunity to integrate various functional properties of ZnO with the advanced silicon-based microelectronics devices. However, direct growth of epitaxial ZnO films on silicon is extremely difficult; often it results in inferior quality films.6 Here, we report the epitaxial growth of ZnO films by employing buffer layers of AlN and GaN in a pulsed laser deposition process. This is the first report of growth of epitaxial ZnO on Si(111) with an AlN buffer layer;
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J. Mater. Res., Vol. 17, No. 10, Oct 2002 Downloaded: 16 Feb 2015
however, epitaxial growth of ZnO on Si(111)/GaN has been reported earlier.7 We have also deposited ZnO directly on hydrogen-terminated Si(111) surfaces. One of the most crucial factors that affect the performance of thin-film devices is the presence of biaxial strain (and associated stress) in the films.8,9 It has been realized that the band structure of ZnO may change with the strain and subsequently may modify the optical and electrical characteristics of the film. We have investigated the strain present in these films as reflected on photoluminescence and Raman scattering measurements. The shi
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