Advanced ion beam technology for versatile oxide thin film formation

Various oxide films, such as SnO₂, In₂O₃, Al₂O₃, SiO₂, ZnO, and Sn-doped In₂O₃ (ITO) have been deposited on glass and polymer substrates by advanced ion beam technologies including ion-assisted deposition (IAD), hybrid ion beam, ion beam sputter deposition (IBSD), and ion-assisted reaction (IAR). Physical and chemical properties of the oxide films and adhesion between films and substrates were improved significantly by these technologies. By using the IAD method, non-stoichiometry, crystallinity, and microstructure of the films were controlled by changing assisted oxygen ion energy and arrival ratio of assisted oxygen ion to evaporated atoms. IBSD method has been carried out for understanding the growth mode of the films on glass and polymer substrate. Relationships between microstructure and electrical properties in ITO films on polymer and glass substrates were intensively investigated by changing ion energy, reactive gas environment, substrate temperature, etc. Smooth-surface ITO films (R_rms ⩽ 1 nm and R_p−v ⩽ 10 nm) for organic light-emitting diodes were developed with a combination of deposition conditions with controlling microstructure of a seed layer on glass. IAR surface treatment enormously enhanced the adhesion of oxide films to polymer substrate. In the case of Al₂O₃ and SiO₂ films, the oxygen and moisture barrier properties were also improved by IAR surface treatment. The experimental results of the oxide films prepared by the ion beam technologies and its applications will be represented in detail.     

Surface plasmon resonance based fiber optic sensor utilizing indium oxide

A highly sensitive surface plasmon resonance (SPR) based fiber optic sensor with indium oxide (In₂O₃) layer coated on the core of the optical fiber is presented and theoretically analyzed. The sensitivity of the SPR based fiber optic sensor has been evaluated numerically. It is shown that the proposed SPR based fiber optic sensor with In₂O₃ layer possesses high sensitivity in the near infrared region of spectrum, which needs attention to many environmental and security applications and offers more accurate and highly reproducible measurements. In addition, the sensitivity of the SPR based fiber optic sensor decreases with the increase in the thickness of In₂O₃ layer. With sensitivity as high as 4600 nm/RIU, the 170 nm thick In₂O₃ layer based fiber optic SPR sensor demonstrates better performance.     

Electron trapping center and SnO2-doping mechanism of indium tin oxide

Indium tin oxide (ITO) and Er³⁺-doped ITO powders were prepared by a conventional ceramic method. The density of ITO powders and optical absorption spectra of Er³⁺ ions in Er³⁺-doped ITO were measured as a function of the SnO₂ doping level. The results obtained were discussed in terms of the trapping center for immobile electrons in ITO. Observed densities of ITO powders were in good agreement with those calculated from their lattice parameters, assuming that the immobile electrons were trapped at the excess interstitial oxygen. The optical absorption spectra of Er³⁺-doped ITO indicated that some In³⁺ ions in ITO were surrounded by 7 and/or 8 oxygen ions; the increase in the coordination number of In³⁺ from 6 in In₂O₃ to 7 and/or 8 in ITO must be caused by the introduction of excess interstitial oxygen into the quasi-anion site in the C-typerare-earth lattice upon SnO₂ doping. It was concluded that the immobile electrons in ITO are trapped at the excess interstitial oxygen, and that the mechanism of conduction carrier generation and compensation upon SnO₂ doping into In₂O₃ can be expressed by the defect equation, 2SnO₂?2Sn_In·+2(1-z)e^′+zO_i ^′′+3O_O ^×+(1-z)/2O₂. Received: 26 November 1999 / Accepted: 20 April 2000 / Published online: 13 September 2000     

Resistance switching properties of In2O3 nanocrystals memory device with organic and inorganic hybrid structure

A memory device with In₂O₃ nanocrystals embedded in a biphenyl-tertracarboxylic dianhydride-phenylen diamine (BPDA-PDA) polyimide layer on a ZnO layer was fabricated, and its electrical properties were evaluated. Then, the transmittance efficiency in the structure of the BPDA-PDA polyimide/In₂O₃ nanocrystals/ZnO/ITO/double polishing sapphire substrate was measured to be about 80% between 440 to 800 nm by ultraviolet-visible transmittance spectroscopy. A bipolar switching current bistability by difference resistance appeared in the sweep voltage rage from −7 to 7 V. It was considered that the bipolar behavior of current-voltage may originate from a resistance fluctuation because of the electron charging effect in In₂O₃ nanocrystals by voltage sweeping, Fowler–Nordheim tunneling, space-charge-limited current, and the migration of O²⁻ ions.     

Low temperature deposition of transparent conducting ITO/Au/ITO films by reactive magnetron sputtering

Transparent conducting indium tin oxide/Au/indium tin oxide (ITO) multilayered films were deposited on unheated polycarbonate substrates by magnetron sputtering. The thickness of the Au intermediated film varied from 5 to 20 nm. Changes in the microstructure, surface roughness and optoelectrical properties of the ITO/Au/ITO films were investigated with respect to the thickness of the Au intermediated layer. X-ray diffraction measurements of ITO single layer films did not show characteristic diffraction peaks, while ITO/Au/ITO films showed an In₂O₃ (2 2 2) characteristic diffraction peak. The optoelectrical properties of the films were also dependent on the presence and thickness of the Au thin film. The ITO 50 nm/Au 10 nm/ITO 40 nm films had a sheet resistance of 5.6 Ω/□ and an average optical transmittance of 72% in the visible wavelength range of 400-700 nm. Consequently, the crystallinity, which affects the optoelectrical properties of ITO films, can be enhanced with Au intermediated films.     

The insert of zinc oxide thin film in indium tin oxide anode for organic electroluminescence devices

Zinc oxide films were prepared by rf magnetron sputtering on glass substrates with designed ZnO target using high-purity of zinc oxide (99.99%) powder. Systematic study on dependence of target-to-substrate distance (D_ts) on structural, electrical and optical properties of the as-grown ZnO films was mainly investigated in this work. XRD showed that highly preferred ZnO crystal in the [0 0 1] direction was grown in parallel to the substrate, while the D_ts did not effect to the peak position of XRD. With decreasing D_ts, the growth rate is increased while the electrical resistivity as well as crystal size in the ZnO films was decreased. The XPS data showed that the O/Zn ratio in ZnO films was increased with increasing D_ts in the films. The as-grown ZnO films have an average transmittance of above 85% at the visible region. The optical band gap of the as-grown ZnO films was changed from 3.18 to 3.36 eV with D_ts. With decreasing D_ts, the electrical resistivity was decreased, while the growth rate was increased.A bilayer is used as an anode electrode for organic electroluminescent devices. The bilayer consists of an ultrathin ZnO layer adjacent to a hole-transporting layer and an Indium tin oxide (ITO) outerlayer. We tried to bring low the barrier between the devices as deposited ZnO films on ITO substrates. We fabricated the organic EL structure consisted of Al as a cathode, Al₂O₃ as an electro transport layer, Alq₃ as a luminously layer, TPD as a hole transport layer and ZnO (1 nm)/ITO (150 nm) as an anode. The result of this experiment was not good compared with the case of using ITO, nevertheless, at this structure we obtained the lowest turn-on voltage as the value of 19 V and the good brightness (6200 cd/m²) of the emission light from the devices. Then the quantum efficiency was to be 1.0%.     

Synthesis of corundum structure ITO nanocrystals by hydrothermal process at low pressure and low temperature

The corundum structures of In₂O₃:Sn (ITO) nanoparticles were synthesized by hydrothermal processing of InCl₃ and SnCl₄·5H₂O precursor at low temperature of 250 °C and 40 bar pressure for 3 h. The precursor was precipitated in a white gel of InOOH. After drying at 150 °C in air, it was crystallized in orthorhombic structure. InOOH powder was transformed into dark-gray rhombohedral In₂O₃ by sintering at 420 °C in forming gas for 1 h. The samples were characterized by means of XRD, SEM, and TEM. The particle size of the resulted ITO powder was about 32 nm.     

Dependence of intermediated noble metals on the optical and electrical properties of ITO/metal/ITO multilayers

Sn doped In₂O₃ (ITO) single layer and a sandwich structure of ITO/metal/ITO (IMI) multilayer films were deposited on a polycarbonate substrate using radio-frequency and direct-current magnetron sputtering process without substrate heating. The intermediated metal films in the IMI structure were Au and Cu films and the thickness of each layer in the IMI films was kept constant at 50 nm/10 nm/40 nm. In this study, the ITO/Au/ITO films show the lowest resistivity of 5.6 × 10⁻⁵ Ω cm.However the films show the lower optical transmission of 71% at 550 nm than that (81%) of as deposited ITO films. The ITO/Cu/ITO films show an optical transmittance of 54% and electrical resistivity of 1.5 × 10⁻⁴ Ω cm. Only the ITO/Au/ITO films showed the diffraction peaks in the XRD pattern. The figure of merit indicated that the ITO/Au/ITO films performed better in a transparent conducting electrode than in ITO single layer films and ITO/Cu/ITO films.     

In2O3 透明薄膜晶体管的制备及其电学性能的研究

采用磁控溅射方法在玻璃衬底上生长了In₂O₃晶体薄膜.该薄膜具有(111)晶面择优取向,晶粒尺寸达到33 nm.利用光刻工艺制作了以In₂O₃晶体薄膜为沟道层的底栅式薄膜晶体管.In₂O₃薄膜晶体管具有良好的栅压调制特性,场效应迁移率达到6.3 cm²/(V·s),开关电流比为3×10³,阈值电压为-0.9 V.结果表明,In相似文献   

Work function of sol-gel indium tin oxide (ITO) films on glass

Indium tin oxide (ITO) films (physical thickness, 250-560 ± 25 nm) were deposited on soda lime silica (SLS) glass and silica layer coated (∼200 nm physical thickness) SLS glass substrates by sol-gel technique using alcohol based precursors containing different In:Sn atomic percentages, namely, 90:10, 70:30, 50:50, 30:70. Cubic phase of In₂O₃ was observed up to 50 at.% Sn while cassiterite SnO₂ phase was observed for 70 at.% Sn. Work function of the films was evaluated from inelastic secondary electron cutoff of ultraviolet photoelectron spectroscopy (UPS) energy distribution curve (EDC) obtained under two experimental conditions (i) as-introduced (ii) after the cleaning of the surface by sputtering. Elemental distribution and the presence of oxygen containing contaminant and carbon contaminant of the samples were done by XPS analysis under same conditions. The work function changed little due to the presence of surface contaminants. It was in the range, 3.9-4.2 eV (±0.1 eV).     

Structural and optical properties of glancing angle deposited In2O3 columnar arrays and Si/In2O3 photodetector

Ordered and perpendicular columnar arrays of In₂O₃ were synthesized on conducting ITO electrode by a simple glancing angle deposition (GLAD) technique. The as-deposited In₂O₃ columns were investigated by field emission gun-scanning electron microscope (FEG-SEM). The average length and diameter of the columns were estimated ～400 nm and ～100 nm, respectively. The morphology of the structure was examined by transmission electron microscopy (TEM). X-ray diffraction (XRD) analysis shows the polycrystalline nature of the sample which was verified by selective area electron diffraction (SAED) analysis. The growth mechanism and optical properties of the columns were also discussed. Optical absorption shows that In₂O₃ columns have a high band to band transition at ～3.75 eV. The ultraviolet and green emissions were obtained from the In₂O₃ columnar arrays. The P-N junction was formed between In₂O₃ and P-type Si substrate. The GLAD synthesized In₂O₃ film exhibits low current conduction compared to In₂O₃ TF. However, the Si/GLAD-In₂O₃ detector shows ～1.5 times enhanced photoresponsivity than that of Si/In₂O₃ TF.     

Indium oxide nanostructures

In this report we review the growth of indium oxide (In₂O₃) nanostructures, including octahedral nanocrystals (NCs), nanobelts (NBs), nanosheets (NSs), and nanowires (NWs), by hot-wall chemical vapor deposition (HW-CVD). This system is highly controllable, allowing the user to easily access different growth regimes – each corresponding to the growth of a different nanostructure – by changing growth variables of the HW-CVD system. Hot-wall CVD produces crystalline nanostructures; here we present a survey of microstructural characterizations of the four types of In₂O₃ nanostructures using transmission- and scanning-electron microscopy. Interestingly, the In₂O₃ nanostructures have different preferred growth directions: NCs have (111) faces, NBs are predominantly (200), and NWs are predominantly (110). We end the review by discussing the current shortcomings of HW-CVD growth of In₂O₃ nanostructures. PACS 61.46.-w; 61.82.Rx; 73.31.Hb; 81.02.-b     

Bicrystalline indium oxide nanobelts

Indium oxide (In₂O₃) nanobelts were synthesized by a chemical vapor deposition using thermal oxidation of In at 1000 °C. The nanobelts exhibited a unique bicrystalline structure that consisted of two single-crystalline cubic In₂O₃ nanobelts each having a different growth direction that often split along the twin boundary that exists at the centerline. The width of split nanobelts was 200–500 nm and the thickness was about 1/10 of the width. The growth direction of the bicrystals was [310]/[611] or [310]/[411]. X-ray diffraction and photoluminescence were measured to characterize the crystalline nature of the nanobelts. PACS 61.64.+w; 61.50.-f; 68.90.+g     

Synthesis of ultrafine single crystals and nanostructured coatings of indium oxide from solution precursor

Indium oxide (In₂O₃) has been widely used in sensors, solar cells and microelectronics. There are several techniques available for making In₂O₃ such as vapor, electrochemical and atomic layer deposition, which are not only expensive but also time consuming processes. In this study, an inexpensive and straightforward synthesis approach is being presented to make micron/submicron size single crystals as well as nanostructured adherent coatings of In₂O₃ using Indium Chloride (InCl₃) powders and InCl₃ solution precursor. Both the powders and the solution precursor were calcined in a furnace to obtain the crystals; however, the liquid precursor was also treated by a DC plasma jet to obtain the nanostructured coatings. The phase transformations during thermal decomposition of InCl₃ powders and solution precursor were investigated via differential scanning calorimetry studies. The phase structure and crystallinity of the crystals and coatings were confirmed by X-ray diffraction. Microstructural characterization of the crystals and coatings was done by scanning electron microscopy, transmission electron microscopy and atomic force microscopy techniques. Size of the crystals was observed to be dependent on the heating schemes adapted during calcination. Solution precursor plasma sprayed In₂O₃ coatings showed porosity and ultrafine particulates with grain size ranging between 10 and 75 nm. Resistivity was determined to be ∼0.553 ± 0.337 kΩ cm. Optical transmittance of In₂O₃ coatings was ∼60-78% in the visible region and it was observed to decrease with increasing the number passes or the thickness of the coatings. Based on the optical transmission data, direct band gap of 3.57 eV was determined.     

Gallium-doped indium oxide nanoleaves: Structural characterization,growth mechanism and optical properties

The novel two-dimensional (2-D) Ga-doped In₂O₃ nanoleaves are synthesized by a simple one-step carbonthermal evaporation method using Cu–Sn alloy as the substrates. Two basic parts construct this leaf-like nanostructure: a long central trunk and two tapered nanoribbons in symmetric distribution in relation to the trunk. The Ga–In–O alloy particles are located at or close to the tips of the central trunks and serve as catalysts for the central trunk growth by the self-catalytic vapor–liquid–solid (VLS) mechanism. And the homoepitaxial growth of tapered nanoribbon on the surface of the central trunk can be explained by vapor–solid (VS) mechanism. The room-temperature photoluminescence (PL) measurement of this nanoscaled Ga-doped In₂O₃ transparent conducting oxide (TCO) detected two blue peaks located at 432 nm and 481 nm, respectively, which can be used by Ru-based dye and indicates potential application in dye-sensitized solar cells (DSSCs). The successful preparation of this novel 2-D Ga-doped In₂O₃ nanoleaves not only enriches the synthesis of TCO materials, but also provides new blocks in future architecture of functional nano-devices.     

Modification in cell structure for better performance of spray pyrolysed CuInS2/In2S3 thin film solar cell

We report a new structure for CuInS₂/In₂S₃ solar cell, in which both absorber and buffer layers were deposited using chemical spray pyrolysis (CSP) technique. The usual superstrate structure, having buffer layer just above ITO, was not functioning mainly due to diffusion of Cu into In₂S₃ layer as seen from X-ray photoelectron spectroscopy (XPS) results. However, when the configuration of the cell was ITO/CuInS₂/In₂S₃/Ag, cell parameters obtained were V_oc=0.45 V, J_sc=44.03 mA/cm², fill factor (FF) = 29.5% and η=5.87%. Good results could be obtained by using indium sulfide thin films having maximum photosensitivity. The cell was characterized using X-ray diffraction, optical absorption, current–voltage and spectral response measurements. PACS 81.15.Rs; 82.45.Mp; 84.60.Jt     

Preferential regrowth of indium–tin oxide (ITO) films deposited on GaN (0001) by rf-magnetron sputter

Effects of thermal treatments on the electrical properties and microstructures of indium–tin oxide (ITO)/GaN contacts have been investigated using a rf-magnetron sputter deposition followed by rapid thermal annealing. ITO films annealed at 800 °C revealed Schottky contact characteristics with a barrier height corresponding to ITO’s work function of 4.62 eV. The evolution of electrical properties of ITO/GaN contacts was attributed to the preferential regrowth of In₂O₃ (222)//GaN (0001) with an ideal metal–semiconductor Schottky contact. The feasible use of ITO/GaN as a transparent Schottky contact would be realized by the enhanced regrowth of In₂O₃ at high temperature. Received: 1 September 2000 / Accepted: 15 November 2000 / Published online: 28 February 2001     

Ohmic contact and space-charge-limited current in molybdenum oxide modified devices

The effect of indium-tin oxide (ITO) surface treatment on hole injection of devices with molybdenum oxide (MoO₃) as a buffer layer on ITO was studied. The Ohmic contact is formed at the metal/organic interface due to high work function of MoO₃. Hence, the current is due to space charge limited when ITO is positively biased. The hole mobility of N, N′-bis-(1-napthyl)-N, N′-diphenyl-1, 1′biphenyl-4, 4′-diamine (NPB) at various thicknesses (100–400 nm) has been estimated by using space-charge-limited current measurements. The hole mobility of NPB, 1.09×10⁻⁵ cm²/V s at 100 nm is smaller than the value of 1.52×10⁻⁴ cm²/V s at 400 nm at 0.8 MV/cm, which is caused by the interfacial trap states restricted by the surface interaction. The mobility is hardly changed with NPB thickness for the effect of interfacial trap states on mobility which can be negligible when the thickness is more than 300 nm.     

Chemical and structural properties of ternary post-transition metal oxide thin films: InZnO,InGaO and GaZnO

The chemical states of ternary post-transition metal oxide thin films of InGaO, GaZnO and InZnO were investigated using X-ray photoelectron spectroscopy. Detailed binding energy (BE) analyses revealed certain evolution in chemistry in the ternary oxides compared to the reference binary oxides of In₂O₃, ZnO, or Ga₂O₃. In particular, O 1s BEs were changed with the compositions, which suggests that the charge transfer (CT) between In³⁺/Ga³⁺/Zn²⁺ and O²⁻ ions is significant. Results of extended X-ray absorption fine structure analyses further showed that the first shell coordination (cation–O bond) is roughly maintained even though the ternary oxide films were structurally disordered. This implies that the CT process via O²⁻ ions can influence the charge reconstructions in the ternary oxide systems.     

Highly transparent and conductive indium tin oxide thin films for solar cells grown by reactive thermal evaporation at low temperature

Transparent conductive tin-doped indium oxide (In₂O₃:Sn, ITO) thin films with various Sn-doping concentrations have been prepared using the low cost reactive thermal evaporation (RTE) technique at a low growth temperature of ~160 °C. The structural characteristics, optical and electrical properties of the ITO thin films were investigated. These polycrystalline ITO films exhibited preferential orientation along (222) plane and possessed low resistivities ranging from 3.51 to 5.71 × 10^?4 Ω cm. The decreased mobility was attributed to the scattering by ionized and neutral impurities at high doping concentrations. The optimized ITO thin film deposited with 6.0 wt% Sn-doping concentration exhibited a high average transparency of 87 % in the wavelength range of 380–900 nm and a low resistivity of 3.74 × 10^?4 Ω cm with a high Hall mobility of 47 cm² V^?1s^?1. A hydrogenated amorphous silicon and silicon–germanium (a-Si:H/a-SiGe:H) double-junction solar cell fabricated with the RTE-grown ITO electrodes presented a conversion efficiency of 10.51 %.