Electronic structure of transparent conducting Mo-doped indium oxide films grown by polymer assisted solution process

Molybdenum-doped indium oxide (IMO), an n-type transparent conducting oxide, was deposited using radio-frequency magnetron sputtering. The effects of oxygen concentration in an argon ambient and substrate temperature on film properties were studied. Compared to undoped indium oxide (In2O3) films, IMO films demonstrated higher electron mobility and more than an order-of-magnitude higher carrier concentration. The highest conductivity IMO film demonstrated a mobility of 44 cm2 V−1 s−1 and a carrier concentration of 1.3×1020 cm−3. The properties of both In2O3 and IMO films were very sensitive to the oxygen concentration, but not to the substrate temperature. Average visible transmittance of In2O3 and IMO films were 86% and 80%, respectively. Both optical and x-ray photoelectron spectroscopy analyses indicate a possible second phase in IMO films deposited at lower (⩽1%) oxygen concentrations.

The ability of successive ionic layer deposition (SILD) technology to synthesize gold clusters on the surface of tin(IV) oxide and indium(III) oxide films is discussed. It was shown that during the process, concentration of active sites that are capable of absorbing gold ions, and the size of the gold particles thus formed, may be controlled by both concentration of the solutions used and the number of SILD cycles. Thus, SILD methodology, employing separate and multiple stages of adsorption and reduction of adsorbed species, has considerable potential for customizing the properties of the deposited metal nanoparticles. In particular, it is shown that during the deposition of gold nanoparticles on the surface of tin(IV) oxide and indium(III) oxide films by SILD methodology, conditions can be realized under which the size of gold nanoclusters may be controllably varied between 1–3 nm and 50 nm. A model is proposed for the formation of gold clusters during the SILD process.

Structural characterization of sputtered indium oxide films deposited at room temperature

Electrical and photoelectrical properties of nanocrystalline zinc oxide and indium oxide films are studied. For these oxides the temperature dependences of conductance are observed to be consisting of two parts with different activation energy. Also photoconductivity relaxation of the oxides can be described by a sum of two exponential functions. The spectral dependencies of nanocrystalline zinc oxide and indium oxide photoconductivity are presented. The photoconductivity arises as samples are illuminated with energy less than band gap. The data are discussed on the basis of model by which the localized states in the band gap play major role.

Highly transparent (over 90% transmission in the visible range) and highly conductive (resistivity ≃2×10−4 Ω cm) indium oxide (undoped) films have been produced by thermal evaporation from an In+In2O3 source in a vacuum chamber containing low pressures of O2. These properties are comparable or superior to the best tin-doped indium oxide films ever reported, and excellent reproducibility has been achieved. Hall effect measurements have revealed that the observed low resistivity is primarily a result of the excellent electron mobility (≃70 cm2/V sec), although the electron concentration is also rather high (⩾4×1020/cm3). X-ray diffraction measurements show distinctly polycrystalline In2O3 structure with a lattice constant ranging from 10.07 to 10.11 Å. Electrolytic electroreflectance spectra exhibit at least four critical transitions, from which we have determined the direct and indirect optical band gaps (≃3.56 and 2.69 eV, respectively). Burstein shifts due to the population of electrons in the conduction band are also observed. These and other results along with a discussion of the processing details are reported.

We have studied the local structural environment of Co in Co-doped indium oxide and indium-tin oxide films, obtained by magnetron sputtering. The $\text{Co}\text{ }K$-edge x-ray absorption spectroscopic studies have been correlated with the x-ray photoelectron spectroscopy, magnetic, and electrical transport measurements performed on the same films. Different contributions of oxidized $({\text{Co}}^{2+})$ and metallic $({\text{Co}}^{0})$ cobalt to the observed ferromagnetism in these films are found depending on the host semiconductor and Co content. Homogeneous substitution of Co atoms for the In sites is found in indium-tin oxide films with less than $7\text{ }\text{at}\text{.}\text{ }%$ of Co, obtained preferably by direct, not sequential, cosputtering. In indium oxide films with similar Co content, obtained by sequential deposition, substitution of Co for the In site is accompanied by a larger static local disorder. As the Co content increases, Co-metal clusters are formed.

High performance molybdenum-doped indium oxide (IMO) films were deposited on slide glass substrates from metallic targets by using dc reactive magnetron sputtering at room temperature. The structural, electrical and optical properties have been investigated as functions of target composition and oxygen partial pressure. The deposited films were smooth and amorphous, as determined by scanning electron microscopy and x-ray diffraction, respectively. The results revealed that the as-deposited molybdenum-doped In2O3 films show good electrical property and high optical transmittance, as well as high infrared transmittance. The films prepared at oxygen partial pressure of 3.8 × 10−2 Pa and with 2 wt% Mo-doped target are characteristic of high Hall mobility of 20.2 cm2 V−1 s−1, carrier concentration of 5.2 × 1020 cm−3, and the average optical transmittance excess 90% in the visible region from 400 to 700 nm. Thus IMO films may be a potential material for novel optoelectrical devices such as an organic light-emitting diode.

We developed a novel transparent conductive film, molybdenum-doped indium oxide (IMO). Using normal thermal reactive evaporation without any special treatments, IMO films have been prepared on normal glass microscope slides at about 350 °C with electrical resistivity of 1.7×10−4 Ω cm, mobility over 100 cm2 V−1 s−1, and an average spectral transmittance in the visible region over 80%. From x-ray photoelectron spectroscopy and x-ray diffraction spectra of the IMO films, it is confirmed that the lattice of IMO is the same as that of In2O3 of cubic bixbyite structure, Mo6+ substitutes for In3+ in In2O3, and there are no new compounds in IMO. The valence difference of 3 between Mo6+ and In3+ is of great advantage to the IMO film with high conductivity and high transparency simultaneously.

In this study, a novel approach for the formation of indium oxide(IO) nanoparticles by irradiating IO thin film using 100 MeVAg8+ ions has been reported. High resolution transmission electron microscopy andenergy dispersive x-ray analysis confirm the presence of single-crystalline IOnanoparticles after irradiation. The electronic excitations induced by 100 MeVAg8+ ions followed by thermal relaxation of the energy spike in IO thin film is responsiblefor the formation of latent tracks in the film. The electronic energy loss(Se) of100 MeV Ag8+ ions in IO is greater than the threshold electronic energy loss(Seth) required for the track formation in IO film, but is less thanSeth required for crystalline silicon. Therefore, the tracks are formed in the IO film and not inthe silicon substrate. This results in a stress induced at the IO film and silicon substrateinterface which is responsible for dewetting of the tracks and the formation ofnanoparticles. The theoretically calculated value of nanoparticle diameter using the thermalspike model is found to be in good agreement with the experimentally observed value of30 nm.

Swift heavy ion induced structural modifications in indium oxide films

Mn-implanted, polycrystalline indium tin oxide and indium oxide films

Indium oxide (In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) films grown on MgO substrates by thermal oxidation were excited by femtosecond laser pulses having photon energy lower than the bandgap. The emission of terahertz (THz) pulse was observed using time domain spectroscopy in the reflection-geometry excitation. Results show that THz generation saturates at an excitation fluence of ~400 nJ/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Although two-photon absorption has been ruled out, the actual THz emission mechanism and still has to be verified and is temporarily attributed to carriers from defect level absorption possibly being driven by a strain field due to the lattice mismatch between the In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and the MgO substrate.

Accurate knowledge of the alignment of conduction and valence bands of layers at the heterojunction and warrant knowledge of the band offsets at the interface is essential for Zn1−xSbxO/ZnO based quantum well device designing and modeling. Under this scenario, valence band offsets of Zn1−xSbxO/ZnO heterostructures grown by the pulsed laser deposition technique was measured by photoelectron spectroscopy and consequently, the conduction band offset was calculated by UV-visible spectroscopy. The change in band alignment has been observed with the dopant (Sb) concentration. Ratios of conduction band offset to valence band offset were estimated to be 1.67 and 0.04 for x = 0.03 and 0.06, respectively, for Sb doped films. A Type-II band alignment was observed at the Zn0.97Sb0.03O/ZnO interface, whereas the Type-I band alignment took place at the Zn0.94Sb0.06O/ZnO interface.

Investigation of O7+ swift heavy ion irradiation on molybdenum doped indium oxide thin films

To understand the electronic conduction mechanism in Sn-doped indium oxide thin films, it is important to study the effect of dopant atoms on the neighbouring indium oxide lattice. Ideally Sn is a substitutional dopant at random indium sites. The difference in valence (Sn4+ replaces In3+) requires that an extra electron is donated to the lattice and thus contributes to the free carrier density. But since Sn is an adjacent member of the same row in the periodic table, the difference in the ionic radius (In3+: 0.218 nm; Sn4+: 0.205 nm) will introduce a strain in the indium oxide lattice. Free carrier electron waves will no longer see a perfect periodic lattice and will be scattered, resulting in the reduction of free carrier mobility, which will lower the electrical conductivity (an undesirable effect in most applications).One of the main objectives of the present investigation is to understand the effects of the strain (produced by difference in the ionic radius) on the microstructure of the indium oxide lattice when the doping level is increased to give high carrier densities. Sn-doped indium oxide thin films were prepared with four different concentrations: 9, 10, 11 and 12 mol. % of SnO2 in the starting material. All the samples were prepared at an oxygen partial pressure of 0.067 Pa and a substrate temperature of 250°C using an Edwards 306 coating unit with an electron gun attachment for heating the crucible. These deposition conditions have been found to give optimum electrical properties in Sn-doped indium oxide films. A JEOL 2000EX transmission electron microscope was used to investigate the specimen microstructure.