Optical characterization of aluminum-doped zinc oxide films by advanced dispersion theories

Pflug, Andreas; Sittinger, V.; Ruske, F.; Szyszka, Bernd; Dittmar, Georg

doi:10.1016/j.tsf.2004.01.006

Cited by 61 publications

(28 citation statements)

References 10 publications

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“…Note furthermore that we evaluated the damping frequency C Dr at the plasma frequency X Dr to obtain q opt , whereas several authors determined l opt or q opt by using the lowfrequency damping constant C L . [37][38][39][40][41] Our evaluation is in line with the original publication of Mergel et al 29 and we will see that the obtained resistivity values are reasonable within the general understanding of conductivity in the investigated material.…”

Section: Methodssupporting

confidence: 89%

“…Instead of q opt , most authors compute the mobility l opt . [29][30][31][32][33][34][35][36][37][38][39][40] The determination of l opt by modeling of optical spectra requires the effective mass m*, whereas the resistivity q opt can be evaluated without knowing m*. As the effective mass is prone to considerable uncertainties, 30,35,36,40 we will focus on the resistivity q opt .…”

Section: Methodsmentioning

confidence: 99%

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Role of the dopant aluminum for the growth of sputtered ZnO:Al investigated by means of a seed layer concept

Sommer

Stanley

Köhler

et al. 2015

Journal of Applied Physics

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This work elucidates the effect of the dopant aluminum on the growth of magnetron-sputtered aluminum-doped zinc oxide (ZnO:Al) films by means of a seed layer concept. Thin (<100 nm), highly doped seed layers and subsequently grown thick (∼800 nm), lowly doped bulk films were deposited using a ZnO:Al2O3 target with 2 wt. % and 1 wt. % Al2O3, respectively. We investigated the effect of bulk and seed layer deposition temperature as well as seed layer thickness on electrical, optical, and structural properties of ZnO:Al films. A reduction of deposition temperature by 100 °C was achieved without deteriorating conductivity, transparency, and etching morphology which renders these low-temperature films applicable as light-scattering front contact for thin-film silicon solar cells. Lowly doped bulk layers on highly doped seed layers showed smaller grains and lower surface roughness than their counterpart without seed layer. We attributed this observation to the beneficial role of the dopant aluminum that induces an enhanced surface diffusion length via a surfactant effect. The enhanced surface diffusion length promotes 2D-growth of the highly doped seed layer, which is then adopted by the subsequently grown and lowly doped bulk layer. Furthermore, we explained the seed layer induced increase of tensile stress on the basis of the grain boundary relaxation model. The model relates the grain size reduction to the tensile stress increase within the ZnO:Al films. Finally, temperature-dependent conductivity measurements, optical fits, and etching characteristics revealed that seed layers reduced grain boundary scattering. Thus, seed layers induced optimized grain boundary morphology with the result of a higher charge carrier mobility and more suitable etching characteristics. It is particularly compelling that we observed smaller grains to correlate with an enhanced charge carrier mobility. A seed layer thickness of 5 nm was sufficient to induce the beneficial effects.

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Section: Methodssupporting

confidence: 89%

Section: Methodsmentioning

confidence: 99%

Role of the dopant aluminum for the growth of sputtered ZnO:Al investigated by means of a seed layer concept

Sommer

Stanley

Köhler

et al. 2015

Journal of Applied Physics

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“…The spectra were analyzed by simultaneously fitting all three spectra, where a TaucLorentz oscillator 10 was used for the dispersion of the amorphous silicon layer while the model used to describe the ZnO:Al layer has already been presented elsewhere. 11 From the fits to the optical spectra the film thicknesses of all involved layers were confirmed and the modeled plasma frequency ⍀ p was used to calculate the carrier concentration in the ZnO:Al film, using electron effective masses as described elsewhere. 12 Hall measurements were carried out using a standard van der Pauw geometry at room temperature.…”

Section: Methodsmentioning

confidence: 99%

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

Ruske

Roczen

Lee

et al. 2010

Journal of Applied Physics

175

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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“…A plasmonic resonance has been observed, whose position could be tuned from 1600 nm to 2200 nm in two different ways: i) by controlling the concentration of tin dopants as shown in Figure 10) [37,71,73]; ii) electrochemically by applying a bias--voltage [37]. As for the case of other wide band gap n--type semiconductors, the plasmonic band of ITO can be explained via Mie scattering theory using a frequency dependent damping parameter, which depends on scattering from ionized impurities [55,74,75]. However, Wang et al noted that the plasmon resonance appeared only for body--centered cubic (bcc) NCs and not for rhombohedral ones [72].…”

Section: Localized Surface Plasmon Resonance In Other Nanocrystalsmentioning

confidence: 99%

Plasmonics in heavily-doped semiconductor nanocrystals

et al. 2013

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Abstract:Heavily--doped semiconductor nanocrystals characterized by a tunable plasmonic band have been gaining increasing attention recently. Herein, we introduce this type of materials focusing on their structural and photo--physical properties. Beside their continuous--wave plasmonic response, depicted both theoretically and experimentally, we also review recent results on their transient ultrafast response. This was successfully interpreted by adapting models of the ultrafast response of noble metal nanoparticles. IntroductionThe optical features exhibited by metallic nano--systems have been the subject of an intensive theoretical and experimental research, resulting in applications in several fields, from surface--enhanced spectroscopy, to biological and chemical nano--sensing [1]. Such developments are primarily due to the localized surface plasmon resonance (LSPR), which results in intense optical absorption and scattering as well as sub--wavelength localization of large electrical fields in the vicinity of the nano--object [2--10]. The plasmonic response of these metallic nanostructures is strongly dependent on the type of metal of which they are made, on the dielectric function of the surrounding medium, on the particle shape and, even if to a lesser extent, on the particle size. Nanoparticles of several metals, such as Ag, Au, Cu and Pt, exhibiting plasmonic response in the ultraviolet and in the visible regions of the spectrum have been successfully synthesized in the past decades [11--15]. Elongated metallic nanoparticles have been shown to exhibit plasmonic response in the near infrared, due to excitation of the longitudinal plasmon mode [16--18]. It has been recently reported that direct optical excitation of the metal by intense femtosecond laser pulses induces an ultra--fast modulation of the plasmonic resonance, which can be used for ultra--fast modulation of signals [19], paving the way to ultrafast active plasmonics. A quantitative investigation of such dynamical features is therefore crucial for the development of a new generation of ultra--fast nano--devices. Pump--probe spectroscopy, giving access to the electronic excitation and subsequent relaxation processes in the material, is to date the most suitable tool for the experimental study of the ultrafast dynamical features exhibited by plasmonic nanostructures. So far, several noble metal structures have been investigated, including spherical nanoparticles [20--22] and nanorods [23], revealing that the physical processes of excitation and relaxation are actually similar to those observed in bulk (i.e. in thin films) metallic systems, that are the electron--electron, the electron--phonon and the phonon--phonon interactions [24,25].

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Optical characterization of aluminum-doped zinc oxide films by advanced dispersion theories

Cited by 61 publications

References 10 publications

Role of the dopant aluminum for the growth of sputtered ZnO:Al investigated by means of a seed layer concept

Role of the dopant aluminum for the growth of sputtered ZnO:Al investigated by means of a seed layer concept

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

Plasmonics in heavily-doped semiconductor nanocrystals

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