Direct measurement of density-of-states effective mass and scattering parameter in transparent conducting oxides using second-order transport phenomena

AbstractTransparent conducting oxides (TCO) have relatively low mobilities, which limit their performance optically and electrically, and which limit the techniques that may be used to explore their band structure via the effective mass. We have used transport theory to directly measure the density-of-states effective mass and other fundamental electronic properties of TCO films. The Boltzmann transport equation may be solved to give analytic solutions to the resistivity, Hall, Seebeck, and Nernst coefficients. In turn, these may be solved simultaneously to give the density-of-states effective mass, the Fermi energy relative to either the conduction or valence band, and a scattering parameter, s, which characterizes the relaxation time dependence on the carrier energy and can serve as a signature of the dominate scattering mechanism. The little-known Nernst effect is essential for determining the scattering parameter and, thereby, the effective scattering mechanism(s). We constructed equipment to measure these four transport coefficients on the same sample over a temperature range of 30 – 350 K for thin films deposited on insulating substrates. We measured the resistivity, Hall, Seebeck, and Nernst coefficients for rf magnetron-sputtered aluminum-doped zinc oxide. We found that the effective mass for zinc oxide increases from a minimum value of 0.24me, up to a value of 0.47me, at a carrier density of 4.5 × 1020 cm−3, indicating a nonparabolic conduction energy band. In addition, our measured density-of-states effective values are nearly equal to conductivity effective mass values estimated from the plasma frequency, denoting a single energy minimum with a nearly spherical, constant-energy surface. The measured scattering parameter, mobility vs. temperature, along with Seebeck coefficient values, characterize ionized impurity scattering in the ZnO:AI and neutral impurity scattering in the undoped material.

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Modulation effect on the effective mass of free carriers induced by multicomponent elements in In2O3-based transparent conducting oxides

Computational Materials Science ◽

10.1016/j.commatsci.2017.06.005 ◽

2017 ◽

Vol 137 ◽

pp. 332-339 ◽

Cited By ~ 1

Author(s):

Ying-Bo Lu ◽

Haozhi Yang ◽

Y.Q. Xin ◽

Wei-Yan Cong

Keyword(s):

Effective Mass ◽

Transparent Conducting Oxides ◽

Modulation Effect ◽

Conducting Oxides ◽

Free Carriers ◽

Transparent Conducting

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Measurement of the Effective Mass of Transparent Conducting films of Cadmium Tin Oxide

MRS Proceedings ◽

10.1557/proc-471-117 ◽

1997 ◽

Vol 471 ◽

Cited By ~ 2

Author(s):

W. P. Mulligan ◽

T. J. Coutts

Keyword(s):

Relaxation Time ◽

Effective Mass ◽

Transparent Conducting Oxides ◽

High Mobility ◽

Carrier Relaxation ◽

Conducting Oxides ◽

Transparent Conducting Films ◽

Transparent Conducting ◽

Carrier Effective Mass ◽

Cadmium Stannate

ABSTRACTWe have prepared transparent conducting films of cadmium stannate (Cd2SnO4 with resistivity as low as 1.5×10-4 Ω cm. The resistivity of these films is low because of their surprisingly high mobility (60 cm2 V-1 sec-1) at high carrier concentration (7×1020cm-3). We conducted an investigation to determine whether the high mobility is due to unusually low carrier effective mass or to a long carrier relaxation time. The conductivity effective mass and relaxation time were estimated by Drude free-electron modeling of reflectance and transmittance spectroscopie measurements. The Drude model appears to represent the behavior of cadmium tin oxide very well. The optical effective mass of the electrons in cadmium stannate is about 0.35 mo, which is similar to that of other transparent conducting oxides. By varying the doping level, we were able to fabricate films with various levels of degeneracy, but these showed no significant difference in effective mass.We were also able to determine the carrier effective mass and the relaxation time by measuring four separate electron transport coefficients: conductivity, Hall, Seebeck, and transverse Nernst-Ettingshausen (Nernst). The Fermi level was found to vary from 0.31 to 0.83 eV above the conduction band minimum, and the conduction band was very close to parabolic in this range, with m* ∼ 0.33 mo, in good agreement with the optical result. We conclude that the effective mass of electrons in cadmium stannate is similar to electrons in other transparent conducting oxides and that high mobility results from a relatively long carrier relaxation time.

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Density-of-states effective mass and scattering parameter measurements by transport phenomena in thin films

Review of Scientific Instruments ◽

10.1063/1.1150224 ◽

2000 ◽

Vol 71 (2) ◽

pp. 462-466 ◽

Cited By ~ 52

Author(s):

D. L. Young ◽

T. J. Coutts ◽

V. I. Kaydanov

Keyword(s):

Thin Films ◽

Effective Mass ◽

Density Of States ◽

Transport Phenomena ◽

Scattering Parameter

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Identification and design principles of low hole effective mass p-type transparent conducting oxides

Nature Communications ◽

10.1038/ncomms3292 ◽

2013 ◽

Vol 4 (1) ◽

Cited By ~ 328

Author(s):

Geoffroy Hautier ◽

Anna Miglio ◽

Gerbrand Ceder ◽

Gian-Marco Rignanese ◽

Xavier Gonze

Keyword(s):

Effective Mass ◽

Transparent Conducting Oxides ◽

Design Principles ◽

Hole Effective Mass ◽

Conducting Oxides ◽

Transparent Conducting ◽

P Type

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Fundamental Advances in Transparent Conducting Oxides

MRS Proceedings ◽

10.1557/proc-623-199 ◽

2000 ◽

Vol 623 ◽

Cited By ~ 11

Author(s):

Timothy J. Coutts ◽

David L. Young ◽

Xiaonan Li

Keyword(s):

Zinc Oxide ◽

Tin Oxide ◽

Ternary Phase Diagram ◽

Cadmium Oxide ◽

Transparent Conducting Oxides ◽

Early Years ◽

Large Area ◽

Scattering Parameter ◽

Conducting Oxides ◽

Transparent Conducting

AbstractIncreasingly large-volume markets for large-area, flat-panel displays and photovoltaic panels are likely to be established in the early years of the next century and transparent conducting oxides (TCOs) of improved opto-electronic properties will be required to enable some of these applications to be realized. Our work is focusing on improving both the fabrication-limited properties of the materials (extrinsic), and materials-limited properties (intrinsic). The emphasis on achieving improved electrical and optical properties hinges on achieving higher electron mobility via intrinsic and/or extrinsic properties. To this end, we have investigated the properties of several TCOs including cadmium oxide, tin oxide, zinc oxide, cadmium stannate and zinc stannate. These may be deposited by chemical vapor deposition (CVD) or sputtering and we hope to establish the capability to fabricate compounds and alloys in the cadmium oxide, tin oxide, zinc oxide ternary phase diagram.The properties of the materials have been investigated using a wide variety of techniques including high-resolution electron microscopy, atomic force microscopy and X-ray diffraction, as well as Mössbauer, Raman and UV/visible/NIR spectroscopies. We have measured the transport properties (conductivity, Hall, Seebeck and Nernst coefficients) and have obtained the effective mZLss, relaxation time, Fermi energy, and scattering parameter. This information has been obtained as a function of carrier concentration, which depends on the deposition and annealing procedures. We have found that the mobilities of free-electrons in the cadmiumbearing compounds are greatly superior to those in the other materials, because they have much longer electron relaxation times. In the case of cadmium oxide, there is also great benefit from a much lower effective mass. We are gaining a clearer understanding of the fundamental microscopic attributes needed for TCOs, which will be required in more-demanding, and rapidly emerging, applications.

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