Deheng Zhang

Scattering mechanisms of charge carriers in transparent conducting oxide films

Scattering mechanisms of charge carriers in Transparent Conducting Oxide (TCO) films have been analyzed theoretically. For the degenerate polycrystalline TCO films with relatively large crystallite sizes and high carrier concentrations (higher than 5 × 1018 cm−3), the depletion layers between crystallites are very thin compared to the crystallite sizes, and the grain boundary scattering on electrical carriers makes a small contribution to limit the mobility of the films. Instead of thermionic emission current, a tunneling current dominates the electron transport over grain boundaries. The Petritz model which is based on thermionic emission and extensively quoted in literature should not be applicable. The main scattering mechanisms for the TCO films are ionized impurity scattering in the low-temperature range and lattice vibration scattering in the high-temperature range. The ionized impurity scattering mobility is independent of temperature and the mobility due to thermal lattice vibration scattering is inversely proportional to the temperature. The results obtained from Hall measurements on our ZnO, ITO, SnO2 and SnO2:F films prepared with various methods supports the analysis.

Transparent conducting ZnO:Al films deposited on organic substrates deposited by r.f. magnetron-sputtering

Abstract Transparent conducting ZnO:Al films with good adhesion and low resistivity have been prepared on organic substrates by r.f. magnetron-sputtering. Polycrystalline ZnO:Al films having a preferred orientation were obtained with resistivity 1.84×10 −3 Ω cm, carrier concentration 4.62×10 20 cm −3 and Hall mobility 7.34 cm 2 /v per s. The average transmittance of the films is 84% in the wavelength range of the visible spectrum.

Preparation of transparent conducting ZnO:Al films on polymer substrates by r. f. magnetron sputtering

Abstract Highly transparent conducting Al-doped ZnO films with good adherence and low resistivity have been prepared on polymer substrates by r. f. magnetron sputtering. Mechanically stable polycrystalline conducting ZnO:Al films having a preferred orientation with the (002) planes parallel to the substrates were deposited on polyisocyanate (PI) substrate with resistivities in the range of 4.1×10−3 to 5.110−4 Ω cm, with carrier densities more than 2.6×1020 cm−3 and Hall mobilities between 5.78 and 13.11 cm2 V−1 s−1. The average transmittance exceeded 80% for a 440 nm thick film deposited on polypropylene adipate (PPA) substrate in the visible spectrum. The quality of obtained films depended on substrate temperatures, sputtering power, Ar pressures and compositions of used targets during film fabrication.

Thickness dependence of structural, optical and electrical properties of ZnO:Al films prepared on flexible substrates

The thickness dependence of structural, optical and electrical properties of the ZnO:Al films on polypropylene adipate (PPA) substrates have been studied. It was observed that with an increase in film thickness, the crystallite sizes and the density of the films were increased, the resistivity was decreased, and the average transmittance in the wavelength range of the visible spectrum was also slightly decreased.

Violet luminescence emitted from ZnO films deposited on Si substrate by rf magnetron sputtering

Highly orientated polycrystalline ZnO films have been deposited on Si substrate at room temperature (RT) by rf magnetron sputtering. A strong violet photoluminescence (PL) located at 402 nm and a weak ultraviolet (UV), PL located at 384 nm are observed when excited with 300 nm light. The former PL originated from the electron transition from conduction band tail states to valence band tail states and the latter is produced due to electron transition from conduction band to valence band. With an increase in intensity of the excitation light, the violet emission peak increases super-linearly and the UV emission increases linearly. After high temperature annealing in air, the crystallinity of obtained films is improved, the violet emission becomes weak and the UV emission gets strong.

Bias voltage dependence of properties for depositing transparent conducting ITO films on flexible substrate

Abstract Good transparent conducting indium tin oxide films with good adherence were deposited on water-cooled polypropylene adipate substrate using bias r.f. magnetron sputtering. The films with resistivity as low as 6.3×10 −4 Ω cm and transmittance over 80% have been obtained by adjusting the bias voltage. It was observed that the structural, electrical and optical properties of the films depend on the bias voltage applied to substrate table.

Electrical and optical properties of F-doped textured SnO2 films deposited by APCVD

This paper presents the structural, electrical and optical properties of transparent conducting F-doped textured SnO2 films prepared by atmosphere pressure chemical vapour deposition (APCVD). Polycrystalline SnO2:F films having a variable preferred orientation have been obtained with resistivity as low as 5 × 10−4 Ωcm, with carrier concentrations between 3.5 × 1020 and 7 × 1020 cm−3, and Hall mobilities from 15.7 to 20.1 cm2/V/s. The average transmittance (including diffusion transmittance) is as high as 94% in the wavelength range of the visible spectrum and the maximum infrared reflectance reaches 92% for a film 655 nm thick. The figure of merit ƒTC = T10/sh, (7.12 × 10−2 S) of these films is the highest amongst the results reported on doped SnO2 films.

Preparation and properties of transparent conducting indium tin oxide films deposited by reactive evaporation

Highly transparent conducting indium tin oxide (ITO) films have been prepared on glass substrates by reactively evaporating In-Sn alloy in a system with an oxygen partial pressure of (1–2) × 10−4 Torr and a substrate temperature between 100 and 320 °C. Mechanically stable polycrystalline conducting ITO films having a preferred orientation with the (111) planes parallel to the substrates were deposited with resistivities in the range from 1.12 × 10−4 to 3.07 × 10−4 Ω cm, with carrier densities between 7 × 1020 and 1.27 × 1021 cm−3 and Hall mobilities between 27 and 40 cm2 V−1 s−1 The average transmittance reached 95% for a film 175 nm thick in the wavelength range of the visible spectrum. The resistivities and transmittances of the obtained films depended on the oxygen partial pressures and substrate temperatures during film fabrication.

Bias voltage dependence of properties for ZnO:Al films deposited on flexible substrate

Abstract Highly transparent conducting Al-doped zinc oxide (ZnO:Al) films with good adherence were deposited on water-cooled polypropylene adipate (PPA) substrate using bias r.f. magnetron sputtering. Films with resistivities as low as 4.6×10 −4 Ω cm and transmittance over 80% have been obtained by adjusting the negative bias voltage of the substrate. The dependence of the structural, electrical and optical properties of these films on the substrate bias voltage was studied in detail.

Comparison of the properties for ZnO:Al films deposited on polyimide and glass substrates

Transparent conducting aluminum–doped zinc oxide (ZnO:Al) films have been prepared on polyimide (PI) and Corning 7059 substrates by r.f. magnetron sputtering technique at low substrate temperature (25–210 °C). Polycrystalline ZnO:Al films having a preferred orientation with the c-axis perpendicular to the substrate were deposited with resistivity as low as 8.5 × 10 −4 cm on PI substrates and 7.1 ×10 − 4 cm on glass substrates. The average transmittance exceeded 74 and 85% in the visible spectrum for 360 and 390 nm thick films deposited on PI and glass, respectively. A comparison of the properties of the films deposited on glass and organic substrates was performed.