Epitaxial ZnO thin films

Nistor M, Gherend F, Mandache N B, Hebert C, Perridre J, Seiler W, Metal semiconductor transition in epitaxial ZnO thin films, J. Appl. Phys., 106, 103710, 2009. 

Jin, Z., Fukumura, T., Kawasaki, M Ando, K., Saito, H., Sekiguchi, T., Yoo, Y.Z., Murakami, M., Matsumoto, Y, Hasegawa, T. and Koinuma, H. (2001) High throughput fabrication of transition-metal-doped epitaxial ZnO thin films a series of oxide-diluted magnetic semiconductors and their properties. Applied Physics Letters, 78, 3824. 

ZnO thin films can be prepared by a variety of techniques such as magnetron sputtering, chemical vapor deposition, pulsed-laser deposition, molecular beam epitaxy, spray-pyrolysis, and (electro-)chemical deposition [24,74]. In this book, sputtering (Chap. 5), chemical vapor deposition (Chap. 6), and pulsed-laser deposition (Chap. 7) are described in detail, since these methods lead to the best ZnO films concerning high conductivity and transparency. The first two methods allow also large area depositions making them the industrially most advanced deposition techniques for ZnO. ZnO films easily crystallize, which is different for instance compared with ITO films that can... 

Table 7.4. Results of high-resolution XRD analysis of several series of epitaxial PLD ZnO thin films grown on c-plane, a-plane, and r-plane sapphire at about 650° C substrate temperature, taken from [47]...

Fig. 7.9. RHEED images of optimized ZnO thin film surfaces on r-plane, a-plane, and c-plane sapphire, in the two azimuthal orientations (top and bottom) separated by 45° (left) or 30° (middle and right), respectively. The RHEED patterns of the a-axis textured film on r-plane sapphire (left) indicate an epitaxial and three-dimensional, island-like growth. The ZnO films on a-plane (middle) and c-plane sapphire (right) exhibit a smoother surface structure, as indicated by the streaky RHEED patterns and the observation of additional weak reflections in the top images due to 3 x 3 surface reconstruction [51]...

Zinc nitrate (Zn(N03)2) and dimethylamine borane (DMAB) with a reagent grade from Sigma-Aldrich were used to synthesize the thin film of ZnO on the Pt-IPMC electrodes. The chemical deposition method was used because the conventional methods such as metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), and DC or RF sputtering require temperatures from 200 °C to 800 °C, while IPMC could not withstand such high temperatures. ZnO thin films were synthesized on the Pt IPMC in an aqueous solution composed of 0.1 mol/L zinc nitrate hydrous and 0.1 mol/L DMAB maintained at 60 °C. As the electrical and optical properties of ZnO film depend on the DMBA concentration. ZnO film prepared from the 0.1 mol/L DMAB solution showed the best results. The optimum deposition condition for ZnO as reported in [Izaki and Katayama (2000)] was used. 

Kim J, Li B, Xie YH (2007) A method for fabricating dislocation-free tensile-strained SiGe films via the oxidation of porous Si substrates. Appl Phys Lett 91 252108-252110 Kim MS, Yim KG, Leem JY, Kim S, Nam G, Lee DY, Kim IS, Kim IS (2011) Thickness dependence of properties of ZnO thin films on porous silicon growth by plasma-assisted molecular beam epitaxy. J Korean Phys Soc 59(3) 2354-2361... 

To eliminate the orientational domains often observed in ZnO thin films grown on (0001) sapphire, (11 20) sapphire substrates have been used for ZnO epitaxy. The lattice parameter a = 0.3250 nm of ZnO and parameter c = 1.299 nm of sapphire are related almost exactly by a factor of 4, with a mismatch less than 0.08% at room temperature. On the basis of this fact and coining the term uniaxial locked epitaxy, ... 

Even though n- and later on p-type doping have been reported in ZnO thin films [ 137], there is no demonstration of electrically pumped lasing in ZnO-based structures. However, optically pumped stimulated emission (SE) has been observed by many researchers from ZnO epitaxial layers grown by a variety of methods [138-141]. There have also been earlier demonstrations, dating back to 1966, of SE and lasing in vapor-grown ZnO platelets, which were cleaved parallel to the oaxis and pumped by an electron beam [142-144]. 

As better quality ZnO layers and epitaxial cavities became available, more detailed investigations of optically pumped SE appeared in the literature. SE and lasing, which could survive even at temperatures as high as 550 K, have been observed by Bagnall et al. [139,150] in ZnO thin films grown by plasma-enhanced... 

In thin films of nanostructured ZnO ( 200 nm thick) grown by PLD, a significant enhancement of% compared to the epitaxially grown ZnO films has been observed with THG efficiencies as high as 1.3% at Xa, = 1250 nm, corresponding to = (1.4 0.7) X 10 esu [217]. This enhancement has been attributed to the reduced dimensionality due to nanocrystalline structure, which has been shown to enhance also the second-order nordinearities as discussed above. Such high efficiency of nonlinear optical conversion creates a potential for nanostructures ZnO thin films to be used in nonlinear optical devices. 

Reuss, F., Frank, S., Kirchner, C Wing, R., Gmber, T. and Waag, A. (2005) Magnetoresistance in epitaxially grown degenerate ZnO thin films. Applied Physics Letters, 87, 112104. 

The typical parameters for the PLD of epitaxial ZnO-based thin films on sapphire including information about target preparation are listed in Table 7.3. Within the range of these software controlled parameters, the properties of the deposited films differ widely, as will be shown in Sect. 7.4. Beside the parameters listed in Table 7.3, the film properties will be influenced furthermore by a few more internal effects, which will be listed and discussed in the following according to the scheme effect/problem-cause-solution. Only the careful consideration of all these hidden effects by experienced operators can ensure the highest quality and reproducibility of PLD grown films. 

Table 7.3. Typical PLD parameters for epitaxial ZnO-based thin films, using an excimer laser LPX 305 (see Table 7.1), and the PLD chamber described in Table 7.2...

Narayan (2005) TEM ZnO-sapphire Ge-Si systems Epitaxy and other lattice matching concepts + + n.a. Thin film growth, nanostructuring... 

In this paper, we review the determination of the shape and the structure of metal particles by electron microscopy as illustrated by examples of Pd clusters epitaxially oriented on oxide single crystals and thin films of MgO and ZnO. The metal-oxide interfaces are characterized by HRTEM profile-view imaging, numerical analysis of the images, and image simulations by the multi-slice technique. 

Pd particles were condensed under UHV on ZnO (001) thin films epitaxially grown in situ on mica single crystals. ... 

The methods available for preparation of the different layers in thin-film solar cells include physical methods such as vacuum sputtering, vapor-phase deposition, and molecular beam epitaxy as well as chemical methods such as chemical vapor-phase deposition, metal organic vapor-phase epitaxy, chemical bath deposition (CBD), and electrochemical deposition (ED). This chapter explores the potential of electrodeposition as a route to the fabrication of absorber layers such as CdTe, CIGS, and CZTS for thin-film solar cells. Electrochemistry may also be usefiil for the preparation of transparent layers such as ZnO this topic has been reviewed by Pauporte and lincot [13]. 

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