Optical properties and mechanisms of current flow in Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> films prepared by spray pyrolysis

Thin films Cu₂ZnSnS₄ (up to 0.9 μm thick) with p-type conductivity and band gap E_g = 1.54 eV have been prepared by the spray pyrolysis of 0.1 M aqueous solutions of the salts CuCl₂ · 2H₂O, ZnCl₂ · 2H₂O, SnCl₄ · 5H₂O, and (NH₂)₂CS at a temperature T_S = 290°C. The electrophysical properties of the films have been analyzed using the model for polycrystalline materials with electrically active grain boundaries. The energy and geometric parameters of the grain boundaries have been determined as follows: the height of the barriers is E_b ≈ 0.045–0.048 eV, and the thickness of the depletion region is δ ≈ 3.25 nm. The effective concentrations of charge carriers p₀ = 3.16 × 10¹⁸ cm^–3 and their mobilities in crystallites μ_p = 85 cm²/(V s) have been found using the technique for determining the kinetic parameters from the absorption spectra of thin films at a photon energy hν ≈ E_g. The density of states at grain boundaries N_t = 9.57 × 10¹¹ cm^–2 has been estimated.     

Modification of the “Transcritical” state in Ni<Subscript>75</Subscript>Fe<Subscript>16</Subscript>Cu<Subscript>5</Subscript>Mo<Subscript>4</Subscript> films produced by RF sputtering

The saturation magnetization, the perpendicular and rotational anisotropy constants, and the coercitivity of Ni₇₅Fe₁₆Cu₅Mo₄ thin magnetic films produced by rf sputtering are measured in the initial state and after annealing. A relation between the presence of perpendicular anisotropy and the “transcritical” state in the films is established. It is shown that, after additional thermal treatment, the magnetic softness of the films can be improved.     

Synthesis of highly non-stoichiometric Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> nanoparticles with tunable bandgaps

Non-stoichiometric Cu₂ZnSnS₄ nanoparticles with average diameters of 4–15 nm and quasi-polyhedral shape were successfully synthesized by a colloidal method. We found that a non-stoichiometric composition of Zn to Cu in Cu₂ZnSnS₄ nanoparticles yielded a correlation where Zn content increased with a decrease in Cu content, suggesting formation of lattice defects relating to Cu and Zn, such as a Cu vacancy (V_Cu), antisite with Zn replacing Cu (Zn_Cu), and/or defect cluster of V_Cu and Zn_Cu. The bandgap energy of Cu₂ZnSnS₄ nanoparticles systematically varies between 1.56 and 1.83 eV depending on the composition ratios of Cu and Zn, resulting in a wider bandgap for Cu-deficient Cu₂ZnSnS₄ nanoparticles. These characteristics can be ascribed to the modification in electronic band structures due to formation of V_Cu and Zn_Cu on the analogy of ternary copper chalcogenide, chalcopyrite CuInSe₂, in which the top of the valence band shifts downward with decreasing Cu contents, because much like the structure of CuInSe₂, the top of the valence band is composed of a Cu 3d orbital in Cu₂ZnSnS₄.     

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     

GeC薄膜的射频磁控反应溅射制备及性质

用射频磁控反应溅射法在ZnS衬底上制备了GeC薄膜,研究了工艺参数对Ge靶溅射及GeC薄膜红外透射性能的影响.衬底温度较低时GeC薄膜中含有H,形成了CH₂,CH₃,Ge-CH₃等,使薄膜产生红外吸收;随衬底温度升高,薄膜红外吸收明显减小.靶基距、射频功率、Ar:CH₄气体流量比、总气压对靶面中毒及溅射影响较大,但对GeC薄膜红外吸收影响较小.靶面中毒严重时,所制备无氢GeC薄膜附着性能差,随靶中毒减弱薄膜附着性能变好.优化工艺后,在ZnS衬底上制备了附着性能良好的无氢GeC薄膜,其折射率约为1.78,薄膜中C的含量比Ge的大,二者主要形成了C—Ge键.所制备的GeC/GaP红外增透保护膜系对ZnS衬底有良好的增透效果. 关键词： GeC薄膜 红外透射光谱 射频磁控溅射 XPS     

Optical properties of ZnCr<Subscript>2</Subscript>Se<Subscript>4</Subscript>

We studied the optical properties of antiferromagnetic ZnCr₂Se₄ by infrared spectroscopy up to 28,000 cm^-1 and for temperatures from 5 to 295 K. At the magnetic phase transition at 21 K, one of the four phonon modes reveals a clear splitting of 3 cm^-1 as a result of spin-phonon coupling, the other three optical eigenmodes only show shifts of the eigenfrequencies. The antiferromagnetic ordering and the concomitant splitting of the phonon mode can be suppressed in a magnetic field of 7 T. At higher energies we observed a broad excitation band which is dominated by a two-peak-structure at about 18,000 cm^-1 and 22,000 cm^-1, respectively. These energies are in good agreement with the expected spin-allowed crystal-field transitions of the Cr³⁺ ions. The unexpected strength of these transitions with d-d character is attributed to a considerable hybridization of the selenium p with the chromium d orbitals.     

Absorption spectrum of thin K<Subscript>2</Subscript>CdI<Subscript>4</Subscript> films

The absorption spectrum of thin films of a new compound, K₂CdI₄, was studied. It was established that this compound belongs to direct-bandgap dielectrics and that its low-frequency electronic and excitonic excitations are localized in CdI ₄ ^2? structural blocks of the crystal lattice. It was found that, in M₂CdI₄ compounds (M = K, Rb, Cs), the bandgap width E _g grows and the spin-orbit splitting of the valence band top decreases with increasing ionic radius of the alkali metal.     

Structure and electrical transport properties of bismuth thin films prepared by RF magnetron sputtering

Bismuth thin films were prepared on glass substrates with RF magnetron sputtering and the effects of deposition temperature on surface morphology and their electrical transport properties were investigated. Grain growth of bismuth and the coalescence of grains were observed above 393 K with field emission secondary electron microscopy. Continuous thin films could not be obtained above 448 K because of the segregation of grains. Hall effect measurements showed that substrate heating yields the decrease of carrier density and the increase of mobility in exponential ways until 403 K. Resistivity of sputter deposited bismuth films has its minimum (about 0.7 × 10⁻³ Ω cm) in range of 403-433 K. Annealing of bismuth films deposited at room temperature was carried out in a radiation furnace with flowing hydrogen gas. The change of resistivity was not significant due to the cancellation of the decrease of carrier density and the increase of mobility. However, the abrupt change of electrical properties of film annealed above 523 K was observed, which is caused by the oxidation of bismuth layer.     

La<Subscript>9.33</Subscript>Si<Subscript>6</Subscript>O<Subscript>26</Subscript> electrolyte thin films for IT-SOFC application deposited by a HIPIMS/DC hybrid magnetron sputtering process

Apatite-type La_9.33Si₆O₂₆ thin films were elaborated by co-sputtering of two metallic La and Si targets powered, respectively, by high power impulse magnetron sputtering and direct current sources, in pure Ar atmosphere, followed by a subsequent high temperature oxidation treatment in air. The structural and chemical features of these films have been assessed by X-ray diffraction and scanning electron microscopy (SEM). The film with near lanthanum silicate La/Si atomic ratio deposited on a porous Ni-YSZ cermet substrates was initially amorphous. After thermal oxidation at 1,173 K in air, the coating crystallised under the expected apatite structure. SEM observation revealed that both film compactness and thickness increased after thermal oxidation. The conductivity evolution with temperature of the pure apatite-like lanthanum silicate coatings, as measured by complex impedance spectroscopy, showed that the activation energy of is quite low compared to the literature data.     

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 and structural properties of PbI<Subscript>2</Subscript> thin film produced via chemical dipping method

PbI₂ thin films were deposited on glass substrates via chemical bath deposition. The characteristics of PbI₂ thin films were examined through their structural and optical properties. X-ray diffraction spectra showed the presence of rhombohedral structure and atom planes were subject to change with the pH of the bath. Scanning electron microscope indicated uniform distribution of grains. Optical properties were examined via UV–VIS; optical spectrum of the thin films was measured at the range of 200–1100 nm wavelength. Optimum pH levels for producing thin films were found to be pH 4–5. It has been observed that transmission and optical band gap (E _g) increased with the pH of the bath, which varied between 66–95 and 2.24–2.50 %, respectively; on the other hand film thickness of PbI₂ thin films was decreased with the pH of the bath. Energy-dispersive X-ray spectroscopy analysis were in accordance with theoretical value of PbI₂ at pH = 4 and 5. Refractive index was negatively correlated with pH of the chemical bath; it has been calculated as 1.97, 1.40, 1.29 and 1.24 for the films produced at pH 2, 3, 4 and 5. The results of the study were compared with similar studies in the literature.     

射频磁控溅射法制备ZnS多晶薄膜及其性质

实验采用射频磁控溅射法在玻璃衬底上沉积了ZnS多晶薄膜,研究了沉积气压、退火温度和衬底温度对ZnS薄膜质量的影响.利用X射线衍射(XRD)分析了薄膜的微结构,并计算了内应力值.通过紫外-可见光分光光度计测量了薄膜的透过谱,计算了Urbach能量和禁带宽度.利用扫描电子显微镜(SEM)观察了薄膜的表面形貌.结果表明: 衬底温度为室温时沉积的ZnS薄膜具有较大的压应力,并且内应力值随着工作气压增大而增大,在300 ℃下进行退火处理后内应力松弛,衬底温度为350 ℃时制备的ZnS薄膜内应力小,透过率高,经300 ℃退火处理后结晶质量有所提高. 关键词： ZnS薄膜 射频磁控溅射 内应力     

Fabrication of p-ZnO:ZrN thin films by RF magnetron sputtering

An attempt has been made to fabricate p-ZnO thin films from the ZrN mixed ZnO targets by RF magnetron sputtering. The targets of different ZrN concentrations (0, 1, 2, and 4?mol%) have been prepared by solid-state reaction route. The ZrN-codoped ZnO films grown on semi-insulating Si (100) substrates have been characterized by X-ray diffraction (XRD), photoluminescence (PL), Hall effect measurement, time-of-flight secondary ion mass spectrometer (ToF-SIMS), and atomic force microscopy (AFM). XRD studies reveal that all films are oriented along (002) plane. The Hall measurements showed p-conductivity for 1 and 2?mol% ZrN-codoped ZnO films. Further, it has been found that 1?mol% ZrN-codoped film has low resistivity (7.5?×?10^?2?Ω?cm) and considerable hole concentration (8.2?×?10¹⁸?cm^?3) by optimum incorporation of nitrogen due to best codoping. The red shift in near-band-edge emission observed from PL well acknowledged the p-conduction in 1 and 2?mol% ZrN-codoped ZnO film. The incorporation of N and Zr atoms in the ZnO matrix has been confirmed by ToF-SIMS analysis. The increase in peak to valley roughness (R _pv) with increase of doping concentration has been observed from AFM analysis. ZnO homojunction has also been fabricated with the best codoped p-ZnO film and it showed typical rectification behavior of a diode. The junction parameters have also been determined for the fabricated homojunction.     

Electronic absorption spectrum of thin K<Subscript>2</Subscript>ZnI<Subscript>4</Subscript> films

The absorption spectrum of thin K₂ZnI₄ films has been investigated in the range of 3–6 eV at temperatures from 90 to 340 K. It is established that this compound belongs to direct-gap insulators; low-frequency exciton excitations are localized in the ZnI₄ lattice layers and have a quasi-two-dimensional character. The spectral analysis revealed the existence of two K₂ZnI₄ modifications, which presumably belong to the monoclinic (I) and orthorhombic (II) phases. The temperature dependences of the spectral position and halfwidth of the low-frequency exciton band in K₂ZnI₄ revealed the existence of first-order phase transitions at 215 and 225 K in the monoclinic and orthorhombic phases, respectively.     

Electronic absorption spectrum of Cs<Subscript>2</Subscript>ZnI<Subscript>4</Subscript> thin films

The absorption spectrum of Cs₂ZnI₄ thin films in the energy range 3–6 eV at temperatures from 90 to 340 K has been investigated. It is established that this compound belongs to direct-gap insulators. Low-frequency exciton excitations are localized in ZnI₄ structural elements of the lattice. Phase transitions at 280 K (paraelectric phase ? incommensurate phase), 135 K (incommensurate phase ? monoclinic ferroelastic phase), and 96 K (monoclinic phase ? triclinic ferroelastic phase) have been found from the temperature dependences of the spectral position and halfwidth of the low-frequency exciton band. Additional broadening of the exciton band is observed for ferroelastic phases; it is likely to be due to exciton scattering from strain fluctuations near domain walls.     

Preparing Cu₂ZnSnS₄ films using the co-electrodeposition method with ionic liquids

Cu₂ZnSnS4（CZTS） films are successfully prepared by co-electrodeposition in aqueous ionic solution and sulfurized in elemental sulfur vapor ambient at 400 C for 30 min using nitrogen as the protective gas.It is found that the CZTS film synthesized at Cu/（Zn+Sn）=0.71 has a kesterite structure,a bandgap of about 1.51 eV,and an absorption coefficient of the order of 10 4 cm 1.This indicates that the co-electrodeposition method with aqueous ionic solution is a viable process for the growth of CZTS films for application in photovoltaic devices.     

Dielectric properties of thin ferroelectric Sn<Subscript>2</Subscript>P<Subscript>2</Subscript>S<Subscript>6</Subscript> films deposited by thermal evaporation

The structure, microstructure, and temperature and field dependences of the dielectric properties of thin (0.5–8.0μm) Sn₂P₂S₆ ferroelectric films deposited onto glass and aluminum foil substrates by thermal vacuum evaporation in a quasi-closed volume are studied. The film-thickness and frequency dependences of the dielectric properties and the unipolarity of the C–V characteristics are explained by the presence of near-surface Schottky-type barrier layers.     

UV absorption spectra of thin films of Cs<Subscript>2</Subscript>CdI<Subscript>4</Subscript> and Rb<Subscript>2</Subscript>CdI<Subscript>4</Subscript> ferroelectrics

Thin films of M₂CdI₄ ferroelectrics (M=Cs, Rb) of orthorhombic structure were synthesized, and their electronic optical spectrum was studied. It was established that both compounds belong to direct-gap dielectrics and that their low-frequency excitons are localized on a sublattice made up of (CdI₄)^2? tetrahedra. The temperature dependence of the exciton band parameters was studied for Cs₂CdI₄ within the temperature interval 90–420 K. The phase transitions occurring in this interval manifest themselves as breaks in the temperature behavior of the band spectral positions and weak peaks in the halfwidth and oscillator strength.