Phase and structural characterization of vanadium oxide films grown on amorphous SiO[sub 2]/Si substrates (original) (raw)
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Nano-structural of vanadium pentoxide (V 2 O 5 ) thin films were deposited by chemical spray pyrolysis technique (CSPT). Nd and Ce doped vanadium oxide films were prepared, adding Neodymium chloride (NdCl 3 ) and ceric sulfate (Ce(SO 4 ) 2 ) of 3% in separate solution. These precursor solutions were used to deposit un-doped V 2 O 5 and doped with Nd and Ce films on the p-type Si and glass substrate at 250°C. The structural, optical and electrical properties were investigated. The X-ray diffraction study revealed a polycrystalline nature of the orthorhombic structure with the preferred orientation of (010) with nano-grains. Atomic force microscopy (AFM) was used to characterize the morphology of the films. Un-doped V 2 O 5 and doped with 3% concentration of Nd and Ce films have direct allowed transition band gap. The mechanisms of dc-conductivity of un-doped V 2 O 5 and doped with Nd and Ce films at the range 303 K to 473 K have been discussed.
Fabrication and electrical properties of pure VO2 phase films
2003
We have grown VO2 thin films by laser ablation for electronic device applications. In obtaining the thin films of the pure VO2 phase, oxygen partial pressure is a critical parameter because vanadium oxides have several phases with differing oxygen concentration. It is found that pure VO2 films are epitaxially grown on α-Al2O3 substrate in the narrow ranges of 55-60 mTorr in an Ar + 10% O2 ambient, and that mixed phase films are synthesized when the deposition pressure slightly deviates from the optimum pressure. The (100) oriented VO2 films undergo an abrupt metal-insulator transition (MIT) with resistance change of an order of 10 4 at 338 K. In the films of mixed phases, the small change of the resistance is observed at the same temperature. The polycrystalline films grown on SiO2/Si substrate undergo broaden change of the resistance. Furthermore, the abrupt MIT and collective current motion appearing in metal are observed when the electric field is applied to the film.
Thin Solid Films, 2014
Crystalline vanadium dioxide (VO 2 ) thin films were prepared by annealing amorphous VO 2 films which were deposited by atomic layer deposition on a SiO 2 substrate. A large influence of the oxygen partial pressure in the annealing ambient was observed by means of in-situ X-ray diffraction. In the range between 1 and 10 Pa of oxygen the interesting VO 2 (R) phase crystallized near 450°C. Between 2 and 10 Pa of oxygen, metastable VO 2 (B) was observed as an intermediate crystalline phase before it transformed to VO 2 (R). Anneals in inert gas did not show any crystallization, while oxygen partial pressures above 10 Pa resulted in oxidation into the higher oxide phase V 6 O 13 . Film thickness did not have much effect on the crystallization behavior, but thinner films suffered more from agglomeration during the high-temperature crystallization on the SiO 2 substrate. Nevertheless, continuous polycrystalline VO 2 (R) films were obtained with thicknesses down to 11 nm. In the case where VO 2 (R) was formed, the semiconductor-metal transition was observed by three complementary techniques. This transition near 68°C was characterized by X-ray diffraction, showing the transformation of the crystal structure, by spectroscopic ellipsometry, mapping optical changes, and by sheet resistance measurements, showing resistance changes larger than 2 orders of magnitude between the low-temperature semiconducting state and the high-temperature metallic state.
Frontiers in Materials, 2022
This report investigates the effect of substrate and nitrogen (16 keV N +) ion implantation on the structural, morphological, compositional, and electrical properties of V 2 O 5 thin films which are grown by thermal evaporation on various substrates, including glass, Si, and sapphire (termed V 2 O 5 :Gl, V 2 O 5 :Si, and V 2 O 5 : Sp, respectively). Structural analysis showed the formation of the mixed (α, and β-V 2 O 5) phases on all substrates; however, the β-V 2 O 5 phase is highly dominant in the V 2 O 5 :G and V 2 O 5 :Si samples. A deformation in the β-phase of V 2 O 5 thin film under ion implantation-induced strain results in a change of crystallite size. Irradiation suppresses XRD peaks in relative intensities, indicating partial amorphization of the film with defect formation. Microstructural analysis confirmed the formation of uniform-sized nanorods for V 2 O 5 :Si, whereas isolated crystallites were formed for other types of substrates. Thermal conductivity may influence the size and shapes of V 2 O 5 crystallite forms on different surfaces. Silicon absorbs heat more effectively than sapphire or glass, resulting in nanorod formation. A decrease in optical bandgap and electrical conduction has been observed due to increased oxygen vacancies, induced electron scattering, and trapping centres on N + implantation. The present study thus offers the unique advantage of simultaneous reduction in optical band-gap and conductance of V 2 O 5 thin films, which is important for optoelectronic applications.
physica status solidi c, 2014
The effective work function (EWF) and the energy position of the valence band in 20‐40‐nm thick VO2and V2O5layers grown by atomic layer deposition (ALD) on top of insulating SiO2 and γ‐Al2O3 films were evaluated using the comparison between capacitance‐voltage and internal photoemission measurements. From the capacitance measured at different temperatures on the metal‐VO2(V2O5)‐insulator‐silicon and metal‐insulator‐silicon diodes we found that the both studied vanadium oxides have the same EWF as gold electrodes evaporated on the same oxides. This result is further collaborated by the internal photoemission experiments at the VO2/SiO2 and V2O5/SiO2 interfaces which indicate the energy barrier between the top of the vanadium oxide valence band (in the insulating phase) and the insulator conduction band to be 4.1 ± 0.1 eV. Since the transition from the narrow‐gap VO2 to the wide‐gap V2O5 oxide causes no change in the WF or in the photoemission threshold, we conclude that the ALD‐grown...
Microstructure study of amorphous vanadium oxide films
Applied Surface Science, 1999
Conversion films of vanadium oxides are potentiodynamically generated on vanadium in acetate electrolyte systems at high voltages. The microstructure of the about 5 mm thin anodic films is investigated. X-ray diffraction and transmission Ž . electron microscopy indicate the films are complete amorphous. X-ray photoelectron spectroscopy XPS measurements Ž . show V 2p binding energies of mixed valance vanadium sub oxides. Electron spin resonance ESR experiments on 3r2 isolated films at 130 K point to paramagnetic V 4q centers in a disordered octahedral oxygen surrounding. q 1999 Elsevier Science B.V. All rights reserved.
Synthesis and characterization of vanadium oxide thin films on different substrates
Journal of Materials Science: Materials in Electronics, 2017
In this study, the V8O15 derivative of vanadium oxide was produced on plain glass, indium tin oxide and silicon wafer substrate layers by taking advantage of wet chemical synthesis which is an easy and economical method. The structural properties of the produced films were examined by XRD and SEM analyses. Besides, Al/VOx/p-Si metal-oxide-semiconductor (MOS) structure was obtained by the same synthesis method. Doping densities of these MOS structures were calculated from frequency dependent capacitance–voltage measurements. It was determined that the interface states which were assigned with the help of these parameters vary according to frequency.
Vanadium oxide (VO 2 ) thin films were prepared by atomic layer deposition using TEMAV (tetrakis[ethylmethylamido]vanadium) precursor and ozone as the reactant gas. Study on the precursor as well as oxidizer doses and temperature dependence showed none of them exhibited the characteristics of ideal ALD. The VO 2 phase formation pathways, its process window, and surface roughness are found to be sensitive to the anneal conditions applied and the substrate used. The VO 2 morphology on Al 2 O 3 was found to be island-like whereas on Si/SiO 2 either a nano particle formation or a continuous film was obtained. GIXRD demonstrated the VO 2 crystallization window to be very narrow on Al 2 O 3 and thick SiO 2 while a relatively broad window is obtained on 1 nm SiO 2 . A reversible change in sheet resistance was measured with more than three orders of magnitude for a 30 nm film.
Effects of microstructure and nonstoichiometry on electrical properties of vanadium dioxide films
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1989
Voided growth structures of sputter-deposited films affect strongly their optical and electrical properties. Vanadium dioxide is an interesting material to study effects of film microstructure and nonstoichiometry on electrical properties because its phase transition makes it possible to investigate electrical behavior both in a semiconducting phase and in a metallic phase. We have deposited vanadium oxide films with different vanadium/oxygen ratios for substrate temperatures between 250 and 550°C by dc reactive magnetron sputtering. The resistivity ratios between a semiconducting phase and a metallic phase are limited to 10 3 order by voided boundaries and oxygen vacancies. The voided boundaries are defined by columnar structure and agglomerated grain growth. The results emphasize the necessity of a combination of deposition to obtain the film with a favorable structure and postdeposition annealing to control the film stoichiometry.