Optical and electrical properties of epitaxial (Mg,Cd)xZn1−xO, ZnO, and ZnO:(Ga,Al) thin films on c-plane sapphire grown by pulsed laser deposition

Lorenz, Michael; Кайдашев, Е. М.; Wenckstern, Holger von; Riede, V.; Bundesmann, Carsten; Spemann, D.; Benndorf, G.; Hochmuth, H.; Rahm, A.; Semmelhack, H.‐C.; Grundmann, Marius

doi:10.1016/s0038-1101(03)00198-9

Cited by 140 publications

(59 citation statements)

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“…The highest Q t values occur for DC or pulsed-DC plasma excitation; RF magnetron sputtering reduces Q t already by a factor of 2.5. The lowest trap densities are achieved by magnetron sputtering onto substrates mounted perpendicularly relative to the sputtering target (Minami et al [37], which reduces direct particle bombardment of the growing films), and for pulsed laser deposition [38,39].…”

Section: Amentioning

confidence: 99%

“…Mobility data of films prepared by pulsed laser deposition, recently published by Lorenz et al [39], are also included in Fig.2. Interestingly, these films exhibit mobilities that are comparable to mobility values reported for zinc oxide single crystals, pointing to a higher structural quality and hence a lower grain barrier defect density of these PLD films.…”

Section: Amentioning

confidence: 99%

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Carrier transport in polycrystalline transparent conductive oxides: A comparative study of zinc oxide and indium oxide

Ellmer

Mientus²

2008

Thin Solid Films

335

191

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Highly-doped indium-tin oxide films exhibit resistivities ρ as low as 1. . Thus the grain barrier trap densities of ZnO and ITO are significantly different, which seems to be connected with the defect chemistry of the two oxides and especially with the piezoelectricity of zinc oxide.Keywords Transparent conductive oxides, carrier transport, degenerate semiconductors, grain barriers, electron mobility 2 Therefore, in the present study the carrier transport processes in ITO and ZnO are compared in order to get a deeper understanding of the differences between these TCO materials. For this purpose conductivity and Hall mobility measurements on ZnO:Al and ITO films were undertaken for films deposited on amorphous as well as single crystalline substrates (sapphire) in order to determine the dominant scattering processes (ionized impurities, grain barriers, crystallographic defects). Our own data are compared with literature data reported for ZnO and ITO to show the general trends. Theoretical and semiempirical models are used to fit the experimental data and to derive characteristic material parameters for these three oxides. Introduction Theoretical modelsThe theoretical models on ionized impurity scattering were already reviewed in 2001 by one of the authors when estimating the mobility limit of highly-doped zinc oxide [3]. In the following a short summary is given to lay the basis for the further discussion.Ionized impurity scattering. This scattering process is caused by ionized dopant atoms and dominates for carrier concentrations above about 10 19 cm -3. An analytical expression for the mobility µ ii of degenerately doped semiconductors, taking into account the non-parabolicity of the conduction band, was given by Zawadzki [7] and refined by Pisarkiewicz et al. [6]:where the screening functionwith the parameter ξ np =1-m 0 */m*, which describes the non-parabolicity of the conduction band (m*, m 0 * -effective masses in the conduction band and at the conduction band edge, 4 respectively). The prefactor in equ. (1) The fit parameters µ max , µ min and µ min -µ 1 describe the lattice mobility at low carrier concentrations, the mobility limited by ionized impurity scattering and the clustering mobility, discussed above (see Table 2). . The ZnO mobility values were fitted using the empirical formula (3) and the fit parameters are summarized in Table 2 together with the corresponding values for silicon. In the transition region from lattice to ionized scattering for 5 . 10 16 < N < 5 . 10 18 cm -3 a large scattering of the experimental ZnO data can be observed. Therefore, the data have been fitted in analogy to the silicon data, which exhibit a much higher accuracy [14].However, the exact transition does not influence the conclusions much since we are interested predominantly in ionized impurity scattering in the region N > 10 19 cm -3 .5 Neutral impurity scattering. Neutral shallow-impurity scattering is often discussed in papers about transport in TCO films at room temperature [17,18]. The mobility due to ...

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Section: Amentioning

confidence: 99%

Section: Amentioning

confidence: 99%

Carrier transport in polycrystalline transparent conductive oxides: A comparative study of zinc oxide and indium oxide

Ellmer

Mientus²

2008

Thin Solid Films

335

191

View full text Add to dashboard Cite

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“…In this respect some of the results given in Table II are remarkable in that the deposition processes and postdeposition treatments used seem to limit defect densities at the grain boundaries to a minimum. Note that some of the results have been achieved by heteroepitaxial growth on sapphire 28,40 or placing substrates perpendicular to the target in magnetron sputtering. 41,42 Adding the postdeposition treatment at high temperatures while preventing degradation of the film via a capping layer has been the key in this work to achieve high carrier mobilities above 65 cm 2 / Vs even at carrier concentrations above 5 ϫ 10 20 cm −3 .…”

Section: Fig 4 ͑Color Online͒ Mobility Determined Hall Measurementsmentioning

confidence: 99%

Improved electrical transport in Al-doped zinc oxide by thermal treatment

Ruske

Roczen

Lee

et al. 2010

Journal of Applied Physics

176

100

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A postdeposition thermal treatment has been applied to sputtered Al-doped zinc oxide films and shown to strongly decrease the resistivity of the films. While high temperature annealing usually leads to deterioration of electrical transport properties, a silicon capping layer successfully prevented the degradation of carrier concentration during the annealing step. The effect of annealing time and temperature has been studied in detail. A mobility increase from values of around 40 cm2/Vs up to 67 cm2/Vs, resulting in a resistivity of 1.4×10−4 Ω cm has been obtained for annealing at temperatures of 650 °C. The high mobility increase is most likely obtained by reduced grain boundary scattering. Changes in carrier concentration in the films caused by the thermal treatment are the result of two competing processes. For short annealing procedures we observed an increase in carrier concentration that we attribute to hydrogen diffusing into the zinc oxide film from a silicon nitride barrier layer between the zinc oxide and the glass substrate and the silicon capping layer on top of the zinc oxide. Both are hydrogen-rich if deposited by plasma-enhanced chemical vapor deposition. For longer annealing times a decrease in carrier concentration can occur if a thin capping layer is used. This can be explained by the deteriorating effect of oxygen during thermal treatments which is well known from annealing of uncapped zinc oxide films. The reduction in carrier concentration can be prevented by the use of capping layers with thicknesses of 40 nm or more.

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“…ZnO:Ga 2 O 3 (0.5%) films have been prepared with resistivity as low as 3x10 -3 ohm cm without degradation of crystal structure [2]. These films had high Hall mobility (70 cm 2 /Vs) and high transmission (~80%) in visible region of spectrum [2].…”

Section: Page 3 Of 15mentioning

confidence: 99%

Dynamics of ZnO laser produced plasma in high pressure argon

Kaydashev

Lunney

2011

Applied Surface Science

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A c c e p t e d M a n u s c r i p t This paper describes the results of some experiments to investigate the laser plume dynamics in the high gas pressure (510 3 -10 4 Pa) regime used for PLD of ZnO nanorods. Time-and spaceresolved UV/visible emission spectroscopy and Langmuir probe measurements were used to diagnose the plasma and follow the plume dynamics. By measuring the spatial profiles of Zn I and Zn II spectral lines it was possible to follow the propagation of the external and internal shock waves associated with the interaction of the ablation plume with the gas. The plume dynamics was also studied for ZnO targets doped with elements which are lighter (Mg), comparable to (Ga), and heavier (Er) than Zn, to see if there is any elemental segregation in the plume. *Research HighlightsPage 2 of 15 A c c e p t e d M a n u s c r i p t AbstractPulsed laser deposition of ZnO in high pressure gas offers a route for the catalyst-free preparation of ZnO nanorods less than 10 nm in diameter. This paper describes the results of some experiments to investigate the laser plume dynamics in the high gas pressure (510 3 -10 4 Pa) regime used for PLD of ZnO nanorods. In this regime the ablation plume is strongly coupled to the gas and the plume expansion is brought to a halt within about 1 cm from the target. A 248 nm excimer laser was used to ablate a ceramic ZnO target in various pressures of argon. Time-and space-resolved UV/visible emission spectroscopy and Langmuir probe measurements were used to diagnose the plasma and follow the plume dynamics. By measuring the spatial profiles of Zn I and Zn II spectral lines it was possible to follow the propagation of the external and internal shock waves associated with the interaction of the ablation plume with the gas. The Langmuir probe measurements showed that the electron density was 10 9 -10 10 cm -3 and the electron temperature was several eV. At these conditions the ionization equilibrium is described by the collisional-radiative model.The plume dynamics was also studied for ZnO targets doped with elements which are lighter (Mg), comparable to (Ga), and heavier (Er) than Zn, to see if there is any elemental segregation in the plume.

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Optical and electrical properties of epitaxial (Mg,Cd)xZn1−xO, ZnO, and ZnO:(Ga,Al) thin films on c-plane sapphire grown by pulsed laser deposition

Cited by 140 publications

References 14 publications

Carrier transport in polycrystalline transparent conductive oxides: A comparative study of zinc oxide and indium oxide

Carrier transport in polycrystalline transparent conductive oxides: A comparative study of zinc oxide and indium oxide

Improved electrical transport in Al-doped zinc oxide by thermal treatment

Dynamics of ZnO laser produced plasma in high pressure argon

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