Structural and electrical properties of fluorine-doped zinc tin oxide thin films prepared by radio-frequency magnetron sputtering

Transparent and conductive thin films of fluorine doped zinc tin oxide (FZTO) were deposited on glass substrates by radio-frequency (RF) magnetron sputtering using a 30 wt% ZnO with 70 wt% SnO₂ ceramic targets. The F-doping was carried out by introducing a mixed gas of pure Ar, CF₄, and O₂ forming gas into the sputtering chamber while sputtering ZTO target. The effect of annealing temperature on the structural, electrical and optical performances of FZTO thin films has been studied. FZTO thin film annealed at 600 °C shows the decrease in resistivity 5.47 × 10⁻³ Ω cm, carrier concentration ∼10¹⁹ cm⁻³, mobility ∼20 cm² V⁻¹ s⁻¹ and an increase in optical band gap from 3.41 to 3.60 eV with increasing the annealing temperatures which is well explained by Burstein–Moss effect. The optical transmittance of FZTO films was higher than 80% in all specimens. Work function (ϕ) of the FZTO films increase from 3.80 eV to 4.10 eV through annealing and are largely dependent on the amounts of incorporated F. FZTO is a possible potential transparent conducting oxide (TCO) alternative for application in optoelectronics.     

Optical properties of thin Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript>, films produced by RF magnetron sputtering

Optical properties of thin Cu₂ZnSnS₄ films produced by RF magnetron sputtering of preliminarily synthesized material are studied. Transmission and reflection coefficients are studied in a range from 0.4 to 26 μm. The optical band-gap width depending on substrate temperature is estimated; in optimal modes, it is equal to 1.47 eV. The study of electrical properties shows that Cu₂ZnSnS₄ possesses low charge-carrier mobility, μ = 1.9 cm²/(V s), at room temperature and hole concentration р = 5 × 10¹⁸ cm^–3. Electron microscopy shows that the film possesses a polycrystalline structure with a crystallite size on the order of 100 nm.     

Structural,photoconductive, thermoelectric and activation energy measurements of V-doped transparent conductive SnO<Subscript>2</Subscript> films fabricated by spray pyrolysis technique

This report investigated the structural, optical and electrical properties of V-doped SnO₂ thin films deposited using spray pyrolysis technique. The SnO₂:V films, with different V-content, were deposited on glass substrates at a substrate temperature of 550°C using an aqueous ethanol solution consisting of tin and vanadium chloride. X-ray diffraction studies showed that the SnO₂:V films were polycrystalline only with tin oxide phases and the preferred orientations are along (1 1 0), (1 0 1), (2 1 1) and (3 0 1) planes. Using Scherrer formula, the grain sizes were estimated to be within the range of 25–36 nm. The variation in sheet resistance and optical direct band gap are functions of vanadium doping concentration. Field emission scanning electron microscopy (FESEM) revealed the surface morphology to be very smooth, yet grainy in nature. Optical transmittance spectra of the films showed high transparency of about ～69–90% in the visible region, decreasing with increase in V-doping. The direct band gap for undoped SnO₂ films was found to be 3.53 eV, while for higher V-doped films it shifted toward lower energies in the range of 3.27–3.53 eV and then increased again to 3.5 eV. The Hall effect and Seebeck studies revealed that the films exhibit n-type conductivity. The thermal activation energy, Seebeck coefficient and maximum of photosensitivity in the films were found to be in the range of 0.02–0.82 eV (in the low-temperature range), 0.15–0.18 mV K^?1 (at T = 350 K) and 0.96–2.84, respectively.     

Effect of balanced and unbalanced magnetron sputtering processes on the properties of SnO2 thin films

A comparative study has been carried on the role of balanced magnetron (BM) and unbalanced magnetron (UBM) sputtering processes on the properties of SnO₂ thin films. The oxygen partial pressure, substrate temperature and deposition pressure were kept 20%, 700 °C and 30 mTorr, respectively and the applied RF power varied in the range of 150–250 W. It is observed that the UBM deposition causes significant effect on the structural, electrical and optical properties of SnO₂ thin films than BM as evidenced by X-ray diffraction, C-V, Spectroscopic Ellipsometer and Photoluminescence measurements. The value of band gap (E_g) of the films deposited at 150 W in UBM is found as E_g = 3.83 eV which is much higher than the value of E_g = 3.69 eV as observed in BM sputtering indicating that UBM sputtering results in good crystalline quality. Further, the C-V measurements of SnO₂ thin films deposited using UBM at high power 250 W show hysteresis with large flat band shift indicating that these thin films can be used for the fabrication of memory device. The observed results have been attributed to different mechanisms which exist simultaneously under unbalanced magnetron sputtering due to ion bombardment of growing SnO₂ thin film by energetic Ar+ ions.     

The study of optical properties of amorphous thin films of mixed oxides In<Subscript>2</Subscript>O<Subscript>3</Subscript>—SnO<Subscript>2</Subscript> system,deposited by co-evaporation

A discussion of optical properties of mixed oxides In₂O₃—SnO₂ system is presented. Film thickness, substrate temperature, composition (in molar %) and annealing have a profound effect on the structure and optical properties of these films. Initially the increase in band gap with the increase of SnO₂ content in In₂O₃ is due to the increase in carrier density as a result of donor electrons from tin. The decrease in band gap above the critical Sn content is caused by the defects formed by Sn atoms, which act as carrier traps rather than electron donors. The increase in band gap with film thickness is caused by the increase in free carrier density which is generated by (i) Sn atom substitution of In atom, giving out one extra electron and (ii) oxygen vacancy acting as two electrons donor. The decrease in band gap with substrate temperature and annealing is due either to the severe deficiency of oxygen, which deteriorate the film properties and reduce the mobility of the carriers, or to the formation of indium species of lower oxidation state (In²⁺).     

Volume of precursor solution effect on the properties of SnO<Subscript>2</Subscript> thin films prepared by nebulized spray pyrolysis technique

Undoped SnO₂ thin films have been deposited on amorphous glass substrates with different precursor solution volume (10, 15, 20 and 25 ml) using simple and cost-effective nebulized spray pyrolysis technique. The influence of precursor solution on structural, optical, photoluminescence and electrical properties had been studied. The X-ray diffraction spectra prove the polycrystalline nature of SnO₂ with tetragonal structure. All the films show a preferred growth orientation along (110) diffraction plane. The average transmittance of SnO₂ thin films varied between 82 and 75% in the visible as well as IR region. The band gap energy decreases from 3.74 to 3.64 eV corresponding to direct transitions with the precursor solution volume had increased from 10 to 20 ml and then increased as 3.72 eV for 25 ml. SEM pictures demonstrated polyhedrons like grains. EDX confirmed the existence of Sn and O elements in all the prepared SnO₂ thin films. Photoluminescence spectra at room temperature revealed that the four emission bands in all the samples such as sharp dominant peak at 361 nm with shoulder peak at 377 nm (UV region), a broad and low intensity peak at 492 nm (blue region) and 519 nm (green region). The electrical parameters were examined by Hall effect measurements, which demonstrated that the film prepared at 20 ml precursor solution volume possess minimum resistivity 2.76?×?10^?3 Ω-cm with activation energy 0.10 eV and maximum figure of merit 1.54?×?10^?2 (Ω/sq)^?1.     

Effect of Ge doping on the electrical properties of amorphous Zn–Sn–O thin films

We report the effect of germanium doping on the active layer of amorphous Zinc–Tin-Oxide (a-ZTO) thin film transistor (TFT). Amorphous thin film samples were prepared by RF magnetron sputtering using single targets composed of Zn₂Ge_0.05Sn_0.95O₄ and Zn₂SnO₄ with variable oxygen contents in the sputtering gases. In comparison with undoped, Ge-doped a-ZTO films exhibited five order of magnitude lower carrier density with a significantly higher Hall-mobility, which might be due to suppressed oxygen vacancies in the a-ZTO lattice since the Ge substituent for the Sn site has relatively higher oxygen affinity. Thus, the bulk and interface trap densities of Ge-doped a-ZTO film were decreased one order of magnitude to 7.047 × 10¹⁸ eV⁻¹cm⁻³ and 3.52 × 10¹¹ eV⁻¹cm⁻², respectively. A bottom-gate TFT with the Ge-doped a-ZTO active layer showed considerably improved performance with a reduced SS, positively shifted V_th, and two orders of magnitude increased I_on/I_off ratio, attributable to the doped Ge ions.     

Effect of deposition time on structural and physical properties of Cu<Subscript>2</Subscript>CdSnS<Subscript>4</Subscript> thin films prepared by spray pyrolysis technique: experimental and ab initio study

Cu₂CdSnS₄ (CCdTS) thin films were synthesized using chemical spray pyrolysis deposition technique. The effect of various deposition times (20, 40, 60 min) on growth of these films was investigated. The as-synthesized Cu₂CdSnS₄ thin films were characterized by X-ray diffraction (XRD), ultraviolet–visible (UV–Vis) spectroscopy, Raman spectroscopy and Hall Effect measurements. The XRD pattern of Cu₂CdSnS₄ structured in stannite phase with preferential orientations along (112) planes. Raman spectrum revealed very strong peak at about 333 cm^?1. The films have the direct optical band gaps of 1.39–1.5 eV. The optimum hole mobility was found to be 3.212 × 10¹ cm² v^?1 s^?1 for the film deposited on 60 min. The electronic structure and optical properties of the stannite structure Cu₂CdSnS₄ were obtained by ab initio calculations using the Korringa–Kohn–Rostoker method combined with the Coherent Potential Approximation (CPA), as well as CPA confirms our results.     

Optical properties of SrTiO<Subscript>3</Subscript> thin films by pulsed laser deposition

SrTiO₃ thin films were prepared on a fused-quartz substrate by pulsed laser deposition (PLD). Dense and homogeneous films with a thickness of 260 nm were prepared. Optical constants (refractive index n and extinction coefficient k) were determined from the transmittance spectra using the envelope method. The optical band gap energy of the films was found to be 3.58 eV, higher than the 3.22 eV for bulk SrTiO₃, attributable to the film stress exerted by the substrate. The dispersion relation of the refractive index vs. wavelength follows the single electronic oscillator model. The refractive index and the packing density for the PLD-prepared SrTiO₃ thin films are higher than those for the SrTiO₃ films prepared by physical vapor deposition, sol–gel and RF sputtering. Received: 18 March 2002 / Accepted: 7 October 2002 / Published online: 8 January 2003 RID="*" ID="*"Corresponding author. Fax: +86-25/359-5535, E-mail: mszhang@nju.edu.cn     

Gamma irradiation effects on structural and optical properties of amorphous and crystalline Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> thin films

The structural and optical properties of RF sputtered Nb₂O₅ thin films are studied before and after gamma irradiation. The films are subjected to structural and surface morphological analyses by using X-ray (XRD) and field emission scanning electron microscope techniques. In the wavelength range of 300–2000 nm, the optical parameters for amorphous and crystalline Nb₂O₅ thin films are estimated at differently exposed γ-irradiation doses (0, 50, 100 and 200 kGy). The optical constants, such as optical energy band gap, absorption coefficient, refractive index and oscillators parameters of amorphous and crystalline Nb₂O₅ thin films are calculated. The optical band gaps of γ-irradiated amorphous and crystalline Nb₂O₅ thin films are determined. In the non-absorbing region, the real part of the refractive index of amorphous and crystalline Nb₂O₅ thin films slightly increases with the increase in the exposed γ-irradiation dose.     

Preparation and optical properties of nanocrystalline thin films in the ZnO-TiO<Subscript>2</Subscript> system

Nanocrystalline compound thin films of ZnO-TiO₂ with different Zn/Ti atomic ratios were prepared by radio frequency magnetron reactive sputtering. The optical constants and the optical band gap were investigated using spectroscopic ellipsometry and the optical absorption spectrum. It was found that the cubic ZnTiO₃ phase can be obtained with the atomic ratio of Zn to Ti of about 1:1, and transforms to rhombohedral ZnTiO₃ phase and a phase mixture of rhombohedral ZnTiO₃ and ZnO with increasing Zn content. The refractive index decreases with the increase of Zn content, and the extinction coefficient in the visible range is near zero. The optical band gap was derived from the modeling of ellipsometry data and extinction coefficient spectra, and compared with that obtained from optical absorption spectrum, and it was found that the optical band gaps obtained by these three methods are consistent with each other. PACS 42.70.-a; 68.55.Jk; 78.20.Ci; 81.15.Cd     

The effects of post-thermal annealing on the optical parameters of indium-doped ZnO thin films

Indium-doped ZnO thin films are deposited on quartz glass slides by RF magnetron sputtering at ambient temper- ature. The as-deposited films are annealed at different temperatures from 400 C to 800 C in air for 1 h. Transmittance spectra are used to determine the optical parameters and the thicknesses of the films before and after annealing using a nonlinear programming method, and the effects of the annealing temperatures on the optical parameters and the thickness are investigated. The optical band gap is determined from the absorption coefficient. The calculated results show that the film thickness and optical parameters both increase first and then decrease with increasing annealing temperature from 400 C to 800 C. The band gap of the as-deposited ZnO:In thin film is 3.28 eV, and it decreases to 3.17 eV after annealing at 400 C. Then the band gap increases from 3.17 eV to 3.23 eV with increasing annealing temperature from 400 C to 800 C.     

<Superscript>119</Superscript>Sn CEMS study of Sb doped SnO<Subscript>2</Subscript> film

Sb doped SnO₂ films prepared by DC sputtering and heating were characterized by ¹¹⁹Sn conversion electron Mössbauer spectrometry (CEMS). An asymmetric doublet was observed in the Mössbauer spectra of 1 %, 3 %, and 10 % Sb doped SnO₂ films. The peak ratios of doublets are considered to be due to the columnar crystal growth on the substrate. With the doping level of Sb, both the isomer shift (δ) and the quadrupole splitting (Δ) increased. After annealing, δ increased and Δ decreased for each sample. These results suggest the followings. The electron doping of the SnO₂ lattice by pentavalent Sb induces the increase of the electron density at the Sn^IV nucleus. The annealing process leads to more complete accommodation of the Sb dopant that results in more effective electron doping and therefore increasing isomer shift for tin. Simultaneously, the distortion of the lattice caused by Sb is relaxed and the quadrupole splitting decreases.     

氧氩比对SnO2/Ag/SnO2透明导电膜光电性能的影响

在室温及不同的氧氩比条件下,采用射频磁控溅射Ag层和直流磁控溅射SnO₂层,在载玻片衬底上制备出了SnO₂/Ag/SnO₂多层薄膜.用霍尔效应测试仪、四探针电阻测试仪和紫外-可见-近红外光谱仪等表征了薄膜的电学性质和光学性质.实验结果表明:当氧氩比为1:14时,所制得的薄膜的光电性质优良指数最大,为1.69×10^-2 Ω^-1;此时,薄膜的电阻率为9.8×10^-5 Ω·cm,方电阻为9.68 Ω/sq,在400~800 nm可见光区的平均光学透射率达85%;并且,在氧氩比为1:14时,利用射频磁控溅射Ag层和直流磁控溅射SnO₂层在PET柔性衬底上制备出了光电性质优良的柔性透明导电膜,其在可见光区的平均光学透过率达85%以上,电阻率为1.22×10^-4 Ωcm,方电阻为12.05 Ω/sq.     

Preparation and properties of CO<Subscript>x</Subscript> films

New types of amorphous graphite-like CO_x films were obtained by two ways: (i) magnetron sputtering of a graphite target in the gas mixture Ar+O₂; and (ii) air annealing at 250–300 °C of a-C films deposited by magnetron sputtering in Ar. These films contain at most 18–22% atomic oxygen, depending on the way of preparation. They remain stable in air and vacuum up to 300 °C. The transition from graphite-like a-C to a-CO_0.2 is accompanied by a sharp increase in electrical resistivity and IR transmittance. Two characteristic absorption bands at approximately 1700 and 1605 cm^-1 appear and the G band in the Raman spectrum shifts to approximately 1605 cm^-1. Electron diffraction reveals that only those films with 002 interlayer distance increased with respect to that of graphite may be saturated with oxygen up to approximately 22 at.%, until they become strongly vaporized. PACS 61.43.Dq; 78.30.Ly; 81.15.Cd; 81.40.Ef     

Chemical bath deposition of SnO2 and Cd2SnO4 thin films

A new approach of chemical bath deposition (CBD) of SnO₂ thin films is reported. Films with a 0.2 μm thickness are obtained using the multi-dip deposition approach with a deposition time as little as 8–10 min for each dip. The possibility of fabricating a transparent conducting oxide layer of Cd₂SnO₄ thin films using CBD is investigated through successive layer deposition of CBD-SnO₂ and CBD-CdO films, followed by annealing at different temperatures. High quality films with transmittance exceeding 80% in the visible region are obtained. Annealed CBD-SnO₂ films are orthorhombic, highly stoichiometric, strongly adhesive, and transparent with an optical band gap of ～4.42 eV. Cd₂SnO₄ films with a band gap as high as 3.08 eV; a carrier density as high as 1.7 × 10²⁰ cm^?3; and a resistivity as low as 1.01 × 10^?2 Ω cm are achieved.     

Photoluminescence of nanostructured Zn<Subscript>2</Subscript>SiO<Subscript>4</Subscript>:Mn<Superscript>2+</Superscript> ceramics under UV and VUV excitation

The photoluminescence of Zn₂SiO₄:Mn²⁺ ceramics with a particle size of 120 ± 10 nm, which is excited in the range of 3.5–5.8 eV and subjected to synchrotron radiation with photon energies of up to 20 eV, is investigated. Nanoscale Zn₂SiO₄:Mn²⁺ ceramics possesses intense luminescence with a maximum of 2.34 eV, the position and half-width of the band are independent of the excitation energy. It is found that the photoluminescence at 2.34 eV decays nonexponentially upon ultraviolet excitation. In the case of nanoscale ceramics is irradiated by vacuum ultraviolet, an additional photoluminescence-excitation channel is likely to occur due to interaction of band states and intrinsic vacancy-like defects of the Zn₂SiO₄ matrix.     

Influence of a dopant source on the structural and optical properties of Mn doped ZnGa<Subscript>2</Subscript>O<Subscript>4</Subscript> thin films

Thin films of ZnGa₂O₄:Mn²⁺ were deposited on quartz substrates using an rf magnetron sputtering technique. The sputtering target, ZnGa₂O₄ doped with 2 at. % manganese, was synthesized by a high temperature solid state reaction. Two different dopant sources were used to incorporate the dopant ions into the target, namely, manganese acetate and manganese oxide. The structural and optical properties of the thin films were studied using XRD, PL and transmission spectra. Polycrystalline ZnGa₂O₄:Mn with a spinel structure could be grown at an optimized substrate–target distance even at room temperature. No luminescence was observed in the as-deposited films grown using (CH₃COO)₂Mn as the dopant source in the target. Substrate heating or post-deposition annealing in the reducing ambient didn’t impart any luminescence to the films, ruling out the possibility of Mn²⁺ incorporation in the films. However, when using MnO as the manganese source in the target, the as-deposited films exhibited green photoluminescent emission (peak maximum at 508 nm) for substrate temperatures at and above 500 °C. This suggests that, in thin films, Mn incorporation and subsequent luminescent outcome is strongly influenced by the dopant source, which is quite different from the bulk phosphor behavior. PACS 81.15.Cd; 78.55.-m; 85.60.-q     

Effect of RF power on the properties of transparent conducting zirconium-doped zinc oxide films prepared by RF magnetron sputtering

Transparent and conducting zirconium-doped zinc oxide films with high transparency and relatively low resistivity have been successfully prepared by radio frequency (RF) magnetron sputtering at room temperature. The RF power is varied from 75 to 150W. At first the crystallinity and conductivity of the film are improved and then both of them show deterioration with the increase of the RF power. The lowest resistivity achieved is 2.07×10^-3\Omegacm at an RF power of 100W with a Hall mobility of 16cm²V^-1s^-1 and a carrier concentration of 1.95×10²⁰cm^-3. The films obtained are polycrystalline with a hexagonal structure and a preferred orientation along the c-axis. All the films have a high transmittance of approximately 92% in the visible range. The optical band gap is about 3.33eV for the films deposited at different RF powers.     

非化学计量比靶材溅射制备Cu-Al-O薄膜的光学电学性质研究

考虑到铜铝溅射速率的差别,使用铜铝比例为0.9 ∶1的多晶CuAlO₂靶材,用射频磁控溅射法制备Cu-Al-O薄膜.研究不同衬底温度对薄膜光学电学性能的影响.在衬底温度500 ℃附近,薄膜在可见光范围内具有很好的透光性,达到70%,计算拟合得到直接帯隙为3.52 eV,与CuAlO₂相的理论值符合较好.在室温附近,薄膜导电符合半导体热激活机理,在衬底温度为500 ℃附近薄膜电导率达到2.48×10^-3 S·cm^-1. 关键词： Cu-Al-O 衬底温度 透过率 电导率