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Notes: We review work on In2O3:Sn films prepared by reactive e-beam evaporation of In2O3 with up to 9 mol % SnO2 onto heated glass. These films have excellent spectrally selective properties when the deposition rate is ∼0.2 nm/s, the substrate temperature is (approximately-greater-than)150 °C, and the oxygen pressure is ∼5×10−4 Torr. Optimized coatings have crystallite dimensions (approximately-greater-than)50 nm and a C-type rare-earth oxide structure. We cover electromagnetic properties as recorded by spectrophotometry in the 0.2–50-μm range, by X-band microwave reflectance, and by dc electrical measurements. Hall-effect data are included. An increase of the Sn content is shown to have several important effects: the semiconductor band gap is shifted towards the ultraviolet, the luminous transmittance remains high, the infrared reflectance increases to a high value beyond a certain wavelength which shifts towards the visible, phonon-induced infrared absorption bands vanish, the microwave reflectance goes up, and the dc resisitivity drops to ∼2×10−4 Ω cm. The corresponding mobility is ∼30 cm2/V s. The complex dielectric function ε is reported.These data were obtained from carefully selected combinations of spectrophotometric transmittance and reflectance data. It is found that ε can be reconciled with the Drude theory only by assuming a strongly frequency-dependent relaxation energy between the plasma energy and the band gap. We review a recently formulated quantitative theoretical model for the optical properties which explicitly includes the additive contributions to ε from valence electrons, free electrons, and phonons. The theory embodies an effective-mass model for n-doped semiconductors well above the Mott critical density. Because of the high doping, the Sn impurities are singly ionized and the associated electrons occupy the bottom of the conduction band in the form of an electron gas. The Sn ions behave approximately as point scatterers, which is consistent with pseudopotential arguments. Screening of the ions is described by the random phase approximation. This latter theory works well as a consequence of the small effective electron radii. Exchange and correlation in the electron gas are represented by the Hubbard and Singwi–Sjölander schemes. Phonon effects are included by three empirically determined damped Lorentz oscillators. Free-electron properties are found to govern the optical performance in the main spectral range. An analysis of the complex dynamic resistivity (directly related to ε) shows unambiguously that Sn ions are the most important scatterers, although grain-boundary scattering can play some role in the midvisible range.As a result of this analysis one concludes that the optical properties of the best films approach the theoretical limit. Band-gap shifts can be understood as the net result of two competing mechanisms: a widening due to the Burstein–Moss effect, and a narrowing due to electron-electron and electron-ion scattering. The transition width—including an Urbach tail—seems to be consistent with these notions. Window applications are treated theoretically from detailed computations of integrated luminous, solar, and thermal properties. It is found that In2O3:Sn films on glass can yield∼78% normal solar transmittance and ∼20% hemispherical thermal emittance. Substrate emission is found to be insignificant. Antireflection with evaporated MgF2 or high-rate sputtered aluminum oxyfluoride can give ∼95% normal luminous transmittance, ∼5% normal luminous reflectance, little perceived color and little increase in emittance. A color purity 〈1% in normal transmission and 〈10% in normal reflection is achievable for a daylight illuminant within extended ranges of film thickness.

Notes: We compute the dynamic resistivity ρ≡ρ1+iρ2 for a model of heavily n-doped semiconductors with special regard to transparent and heat-reflecting In2O3:Sn films. The Sn impurities are ionized and the ensuing electrons occupy part of the In2O3 conduction band as a free-electron gas (with plasma energy (h-dash-bar)ωp). We use pseudopotential arguments to show that the Sn ions act as Coulomb scatterers up to the largest electron densities of practical interest. By representing screening in the electron gas with different models, it was found that exchange and correlation could decrease ρ1 by (approximately-less-than)20% below (h-dash-bar)ωp and alter the exponent s in the relation ρ1∝ωs, applying at (h-dash-bar)ω〉(h-dash-bar)ωp, from −3/2 to ∼ −2.

Notes: ZnO:Al coatings were prepared by rf magnetron sputtering of ZnO together with dc magnetron sputtering of Al onto rapidly revolving unheated substrates under weakly oxidizing conditions. Optimized films had ∼1% luminous absorptance, ∼85% thermal infrared reflectance, and ∼5×10−4 Ω cm electrical resistivity at a thickness of ∼0.3 μm. The Al content was (approximately-less-than)2 at. %, as determined by Rutherford backscattering spectrometry. Transmission electron microscopy and electron diffraction showed ∼50-nm average crystallite size and a hexagonal wurtzite structure. Spectrophotometric transmittance and reflectance were recorded in the 0.2–50-μm wavelength interval, and the complex dielectric function was evaluated by computation. The optical data were explained from an effective mass model for n-doped semiconductors. The Al atoms are singly ionized, and the associated electrons occupy the bottom of the conduction band as free-electron gas. The Al ions act as pointlike Coulomb scatterers and are screened by the electrons according to the random phase approximation or an extension thereof. The optical properties of ZnO:Al could be understood by considering the free electrons to be damped primarily by ionized impurity scattering. ZnO:Al films can have high luminous transmittance, high solar ultraviolet absorptance, low thermal infrared emittance, and high electrical conductance; hence, they are of large interest for energy-efficient windows.

Notes: Heavily doped ZnO:Al films were made by dual-target reactive magnetron sputtering. Spectrophotometry in the 0.3–50 μm range proved that the films were suitable for energy-efficient windows. The optical data could be reconciled with a theory involving a free-electron gas damped by ionized impurity scattering.