Structural, electrical, and optical properties of ZnInO alloy thin films

Indium zinc oxide (IZO) thin films with different percentages of In content (In/[In+Zn]) are synthesized on glass substrates by magnetron sputtering, and the structural, electrical and optical properties of IZO thin films deposited at different In₂O₃ target powers are investigated. IZO thin films grown at different In₂O₃ target sputtering powers show evident morphological variation and different grain sizes. As the In₂O₃ sputtering power rises, the grain size becomes larger and electrical mobility increases. The film grown with an In₂O₃ target power of 100 W displays the highest electrical mobility of 13.5 cm·V^-1·s^-1 and the lowest resistivity of 2.4 × 10^-3 Ω·cm. The average optical transmittance of the IZO thin film in the visible region reaches 80% and the band gap broadens with the increase of In₂O₃ target power, which is attributed to the increase in carrier concentration and is in accordance with Burstein-Moss shift theory.     

Anomalous Hall effect in Cu and Fe codoped In2O3 and ITO thin films

We present a systematic study of the structure, magnetization, resistivity, and Hall effect properties of pulsed laser deposited Fe- and Cu-codoped In₂O₃ and indium-tin-oxide (ITO) thin films. Both the films show a clear ferromagnetism and anomalous Hall effect at 300 K. The saturated magnetic moments are almost the same for the two samples, but their remanent moments M_r and coercive fields H_C are quite different. M_r and H_C values of ITO film are much smaller than that of In₂O₃. The ITO sample shows a typical semiconducting behavior in whole studied temperature range, while the In₂O₃ thin film is metallic in the temperature range between 147 and 285 K. Analysis of different conduction mechanisms suggest that charge carriers are not localized in the present films. The profile of the anomalous Hall effect vs. magnetic field was found to be identical to the magnetic hysteresis loops, indicating the possible intrinsic nature of ferromagnetism in the present samples.     

Top electrode effects on resistive switching behavior in CuO thin films

Top electrode (TE) material on the resistive switching behavior of (TE)/CuO/SnO₂:F/Si substrate has been studied. We investigated the switching properties of CuO films deposited by sol-gel process. Two kinds of top electrode (TE) material on the resistive switching behaviors have been studied. The nonpolar and bipolar resistive switching phenomenon was observed in CuO thin films with different top electrodes. The filamentary mechanism was used to explain the two kinds of resistive switching behaviors. For the Pt/CuO/ATO device, it showed the nonpolar resistive switching where conducting path is formed and disappear due to the oxygen vacancy. For the Cu/CuO/ATO device, the resistance reduction is due to the existing Cu to form conduction Cu-rich pathways. An opposite bias takes the existing Cu back to the Cu electrode to its high-resistance state. CuO thin films are also observed by XRD, AFM and XPS.     

Magnetic and structural study of Cu-doped TiO2 thin films

Transparent pure and Cu-doped (2.5, 5 and 10 at.%) anatase TiO₂ thin films were grown by pulsed laser deposition technique on LaAlO₃ substrates. The samples were structurally characterized by X-ray absorption spectroscopy and X-ray diffraction. The magnetic properties were measured using a SQUID. All films have a FM-like behaviour. In the case of the Cu-doped samples, the magnetic cycles are almost independent of the Cu concentration. Cu atoms are forming CuO and/or substituting Ti in TiO₂. The thermal treatment in air promotes the CuO segregation. Since CuO is antiferromagnetic, the magnetic signals present in the films could be assigned to Cu substitutionally replacing cations in TiO₂.     

Ferromagnetism in carbon-doped In2O3 thin films

Carbon-doped In₂O₃ thin films exhibiting ferromagnetism at room temperature were prepared on Si (100) substrates by the rf-magnetron co-sputtering technique. The effects of carbon concentration as well as oxygen atmosphere on the ferromagnetic property of the thin films were investigated. The saturated magnetizations of thin films varied from 1.23 to 4.86 emu/cm³ with different carbon concentrations. The ferromagnetic signal was found stronger in samples with higher oxygen vacancy concentrations. In addition, deposition temperature and different types of substrates also affect the ferromagnetic properties of carbon-doped In₂O₃ thin films. This may be related to the oxygen vacancies in the thin film system. The experiment suggests that oxygen vacancies play an important role in introducing ferromagnetism in thin films.     

Fabrication of cuprous and cupric oxide thin films by heat treatment

Cuprous oxide (Cu₂O) and cupric oxide (CuO) thin films were prepared by thermal oxidation of copper films coated on indium tin oxide (ITO) glass and non-alkaline glass substrates. The formation of Cu₂O and CuO was controlled by varying oxidation conditions such as, oxygen partial pressure, heat treatment temperature, and oxidation time. The microstructure, crystal direction, and optical properties of copper oxide films were measured with X-ray diffraction, atomic force microscopy, and optical spectroscopy. The results indicated that the phase-pure Cu₂O and CuO films were produced in the oxidation process. Optical transmittance and reflectance spectra of Cu₂O and CuO clearly exhibited distinct characteristics related to their phases. The electrical properties indicated that these films formed ohmic contacts with Cu and ITO electrode materials. Multilayers of Cu₂O/CuO were fabricated by choosing the oxidation sequence. The experimental results in this paper suggest that the thermal oxidation method can be employed to fabricate device quality Cu₂O and CuO films that are up to 200–300 nm thick.     

Improving the electrical conductivity of CuCrO2 thin film by N doping

N-doped CuCrO₂ thin films were prepared by using radio frequency magnetron sputtering technique. The XRD and XPS measurements were used to confirm the existence of the N acceptors in CuCrO₂ thin films. Hall measurements show the p-type conduction for all films. The electrical conductivity increases rapidly with the increase in N doping concentration, and the maximum of the electrical conductivity of 17 S cm⁻¹ is achieved for the film deposited with 30 vol.% N₂O, which is about three orders of magnitude higher than that of the undoped CuCrO₂ thin film. Upon increasing the doping concentrations the band gaps of N-doped CuCrO₂ thin films increase due to the Burstein-Moss shift.     

AC electroluminescence of ZnS: Cu,Cl, Mn thin films in the structure In2O3(Sn)-ZnS: Cu,Cl, Mn-SiOx-Al

AC electroluminescence of ZnS: Cu, Cl, Mn thin films in the structure In₂O₃(Sn) - ZnS: Cu, Cl, Mn-SiO_x Al was studied. Vacuum-evaporated films 0.5 to 2.0 μm thick, excited with sinusoidal voltage of 80–200 V and up to 2 kHz gave the luminance response fulfilling Alfrey-Taylor's relation. Thus the electroluminescence model, suggested by these authors for a ZnS monocrystal, can be applied also for ZnS thin films.     

Identification of Cu(I) and Cu(II) oxides by electron spectroscopic methods: AES,ELS and UPS investigations

The externally prepared black-coloured copper oxide (T? 700 K, P_O2 ? 100 torr) on a Cu(100) surface is identified by electron spectroscopy as CuO. Compared to the red-coloured Cu(I) oxide (in situ oxidation at T ? 400 K, P_O2 ? 0.5 torr, ～ 10⁹ L), the He(I)- excited photoemisson from CuO reveals characteristic shake-up satellites 10–12 eV below E_F and a broadened emission from overlapping oxygen-induced 2p and Cu 3d states. From the AES and ELS results, in correlation with the data from core electron spectroscopy, chemical shifts of Cu 2p, Cu 3s and Cu 3p in CuO to higher binding energy and decreases in binding energy of the oxygen-induced states were deduced. The unoccupied electron states of Cu at 5 and 7.5 eV above E_F — postulated from the ELS results — are preserved in Cu₂O and CuO compounds. Annealing of the Cu(II) oxide at 670 K is accompanied by decomposition into Cu₂O due to the solid-state reaction following the scheme: 2CuO → 1/2 O₂ + Cu₂O.     

Effect of thermal treatment on the electrotransport properties of thin-film In<Subscript>2</Subscript>O<Subscript>3</Subscript>, ZnO materials and the multilayer (In<Subscript>2</Subscript>O<Subscript>3</Subscript>/ZnO)<Subscript>83</Subscript> heterostructure

The effect heat treatment has on the electrotransport mechanisms in films of ZnO and In₂O₃, and in a multilayer (In₂O₃/ZnO)₈₃ structure obtained via ion-beam sputtering, is studied. It is shown that there is a mechanism of weak electron localization in the In₂O₃ and (In₂O₃/ZnO)₈₃ samples. The relaxation processes that occur during the heat treatment of In₂O₃ films are found to increase the length of elastic electron scattering, but to reduce this parameter in multilayer heterostructures.     

Conduction mechanisms in pyrolytically grown dielectrics

Various conduction mechanisms in thin SiO₂, Al₂O₃, In₂O₃ layers were investigated experimentally by analyzing the behavior of the current as a function of field strength and temperature. The films were obtained by pyrolytic dissociation of organic compounds in the vapor phase.The author is indebted to P. S. Kireev for guidance, and to M. I. Elinson and V. B. Sandomirskii for interest in the investigation.     

X-ray induced photoelectron and auger spectra of Cu,CuO, Cu2O,and Cu2S thin films

Improved techniques have been used to prepare thin films of Cu, CuO, Cu₂O and Cu₂S for x-ray photoelectron spectral analysis. The Cu 2p and Cu LMM Auger spectra have been obtained. Photoelectron and Auger chemical shifts as well as qualitative spectral features are found to be useful diagnostics for valence-state characterization of unknowns.     

Co-doped In2O3 thin films: Room temperature ferromagnets

Laser-ablated Co-doped In₂O₃ thin films were fabricated under various growth conditions on R-cut Al₂O₃ and MgO substrates. All Co:In₂O₃ films are well-crystallized, single phase, and room temperature ferromagnetic. Co atoms were well substituted for In atoms, and their distribution is greatly uniform over the whole thickness of the films. Films grown at 550 °C showed the largest magnetic moment of about 0.5 μ_B/Co, while films grown at higher temperatures have magnetic moments of one order smaller. The observed ferromagnetism above room temperature in Co:In₂O₃ thin films has confirmed that doping few percent of magnetic elements such as Co into In₂O₃ could result in a promising magnetic material.     

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.     

Improvement of Cu2ZnSnS4 thin film morphology using Cu–Zn–Sn–O precursor fabricated by sputtering

The new precursor of Cu–Zn–Sn–O (CZTO) was proposed for Cu₂ZnSnS₄ (CZTS) thin film fabrication to improve film morphology. The CZTS thin film grown from Cu–Zn–Sn (CZT) precursors has many bumps. We deposited CZTO precursors on Mo/soda-lime glass (SLG) substrates by RF sputtering using a CZT (Cu:Zn:Sn = 2:1:1) target in Ar and O₂ atmosphere at various O₂ partial pressures (0%, 5%, 17% and 20%). Subsequently, the CZTO precursors were sulfurized in Ar and S atmosphere to fabricate CZTS thin films. The CZTO precursors were amorphous. The morphology of the CZTS thin films was improved by the CZTO precursors. All of the CZTS films fabricated in this study had the same crystal structure. Composition analysis revealed that 50% of O were detected in the CZTO precursor, but O was not detected after sulfurizing process, indicating that O was substituted by S. The CZTS thin film from the CZTO precursor fabricated at O₂ partial pressure of 20% had similar composition for solar cell absorber.     

Structures and photovoltaic properties of copper oxides/fullerene solar cells

Copper oxide (CuO_x) thin films were produced by spin-coating and electrodeposition methods, and their microstructures and photovoltaic properties were investigated. Thin film solar cells based on the Cu₂O/C₆₀ and CuO/C₆₀ heterojunction or bulk heterojunction structures were fabricated on F-doped or In-doped SnO₂, which showed photovoltaic activity under air mass 1.5 simulated sunlight conditions. Microstructures of the CuO_x thin films were examined by X-ray diffraction and transmission electron microscopy, which indicated the presence of Cu₂O and CuO nanoparticles. The energy levels of the present solar cells were also discussed.     

CTAB assisted growth and characterization of nanocrystalline CuO films by ultrasonic spray pyrolysis technique

An aqueous solution of cupric nitrate trihydrate (Cu(NO₃)₂·3H₂O) modified with cetyltrimetylammonium bromide (CTAB) is used to deposit CuO films on glass substrate by chemical spray pyrolysis technique. The thermal analysis shows that the dried CTAB doped precursor decomposes by an exothermic reaction and suggests that minimum substrate temperature for film deposition should be greater than 270 °C. X-ray diffraction (XRD) studies indicate the formation of monoclinic CuO with preferential orientation along (0 0 2) plane for all film samples. The CTAB used as cationic surfactant in precursor results in the suppression of grain growth in films along the (1 1 0), (0 2 0) and (2 2 0) crystal planes of CuO. Surfactant modified films showed an increase in crystallite size of 14 nm at substrate temperature of 300 °C. The scanning electron micrographs (FESEM) confirm the uniform distribution of facets like grains on the entire area of substrate. CTAB modified films show a significant reduction in the particle agglomeration. Electrical studies of the CuO films deposited at substrate temperature of 300 °C with and without surfactant reveal that the CTAB doping increase the activation energy of conduction by 0.217 eV and room temperature response to ammonia by 9%. The kinetics of the ammonia gas adsorption on the film surface follows the Elovich and Diffusion models.     

Synthesis of P-type transparent conducting silver:indium oxide (AIO) thin films by reactive electron beam evaporation technique

Present paper reports the synthesis, electrical and optical properties of p-type conducting and transparent silver indium oxide (AIO) thin films prepared on glass substrates by reactive electron beam evaporation technique at three substrate temperatures (50, 200 and 250 °C) and at five evaporation rates (0.05 to 16.0 nm/s). The source material is pure powders of Ag₂O:In₂O₃=50:50 mol%. The AIO films are amorphous. The films, though not corresponding to Delafossite crystal structure, exhibit p-type conductivity, when prepared at an evaporation rate of 0.05 nm/s at all the three substrate temperatures. With increasing filament current, it is observed that (i) the electrical resistivity decreases and (ii) the refractive index of the films (at 632.8 nm, and is in the range: 1.219-1.211) decreases. The work function (effective Fermi level) has been measured on these samples by Kelvin Probe method. The results are explained on the basis of partial ionic charge and localization of covalent bonds in the AIO thin films.     

Magnetoelectric properties of Mn-substituted BiFeO3 thin films with a TiO2 barrier

Multiferroic thin films with the general formula TiO₂/BiFe_1−xMn_xO₃ (x=0.00, 0.05, 0.10 and 0.15) (TiO₂/BFMO) were synthesized on Au/Ti/SiO₂/Si substrates using a chemical solution deposition (CSD) method assisted with magnetron sputtering. X-ray diffraction analysis shows the thin films contained perovskite structures with random orientations. Compared with BFMO films, the leakage current density of the TiO₂/BFMO thin films was found to be lower by nearly two orders of magnitude, and the remnant polarizations were increased by nearly ten times. The enhanced ferroelectric properties may be attributed to the lower leakage current caused by the introduction of the TiO₂ layer. The J-E characteristics indicated that the main conduction mechanism for the TiO₂/BFMO thin film was trap-free Ohmic conduction over a wide range of electric fields (0-500 kV/cm). In addition, ferromagnetism was observed in the Mn doped BFO thin films at room temperature. The origin of ferromagnetism is related to the competition between distortion of structure and decrease of grain size and decreasing net magnetic moment in films due to Mn doping.     

The In2O3/CdTe interface: A possible contact for thin film solar cells?

Transparent conductive In₂O₃ films were deposited by reactive evaporation of In and analyzed in-situ with photoelectron spectroscopy. The interface formation of In₂O₃ with evaporated CdTe has been investigated using the same technique. A valence band offset ΔE_VB=2.1±0.1 eV is determined, resulting in a negligible conduction band offset. However, In₂O₃ will not provide an Ohmic contact to n-CdTe, due to the Fermi level position at the interface.