Optical, electrical and morphological properties of p-type Mn-doped SnO2 nanostructured thin films prepared by sol–gel process

SnO₂ thin films doped with various manganese concentrations were prepared on glass substrates by sol–gel dip coating method. The decomposition procedure of compounds produced by alcoholysis reactions of tin and manganese chlorides was studied by thermogravimetric analysis (TGA). The effects of Mn doping on structural, morphological, electrical and optical properties of prepared films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Hall effect measurement, Fourier Transform Infrared (FTIR) spectral analysis, UV–Vis spectrophotometry, and photoluminescence (PL) spectroscopy. The results of the X-ray diffraction show that the samples are crystalline with a tetragonal rutile structure and the grain size decreases with increasing the doping concentration. The SEM and AFM images demonstrate that the surface morphology of the films was affected from the manganese incorporation. The Sn_1?x Mn _x O₂ thin films exhibited electrically p-type behavior in doping level above x=0.035 and electrical resistivity increases with increase in Mn doping. The optical transmission spectra show a shift in the position of absorption edge towards higher wavelength (lower energy). The optical constants (refractive index and extinction coefficient) and the film thickness were determined by spectral transmittance and using a numerical approximation method. The oscillator and dispersion energies were calculated using the Wemple–DiDomenico dispersion model. The estimated optical band gap is found to decrease with higher manganese doping. The room-temperature PL measurements illustrate the decrease in intensity of the emission lines when content of Mn is increased in Mn-doped SnO₂ thin films.     

Thickness dependent optical dispersion parameters and nonlinear optical properties of nanostructured Cr doped CdO thin films

Cr doped CdO thin films were deposited on glass substrates by reactive DC magnetron sputtering with varying film thickness from 250 to 400 nm. XRD studies reveal that the films exhibit cubic structure with preferred orientation along the (2 0 0) plane. The optical transmittance of the films decreases from 92 to 72%, whereas the optical energy band gap of the films decreased from 2.88 to 2.78 eV with increasing film thickness. The Wemple–DiDomenico single oscillator model has been used to evaluate the optical dispersion parameters such as dispersion energy (E_d), oscillator energy (E_o), static refractive index (n_o) and high frequency dielectric constant (ε_∞). The nonlinear optical parameters such as optical susceptibility (χ⁽¹⁾), third order nonlinear optical susceptibility (χ⁽³⁾) and nonlinear refractive index (n₂) of the films were also determined.     

Structural and optical analysis of 60Co gamma-irradiated thin films of polycrystalline Ga10Se85Sn5

The present study focuses on the effects of gamma irradiation on structural and optical properties of polycrystalline Ga₁₀Se₈₅Sn₅ thin films with a thickness of ～300?nm deposited by the thermal evaporation technique on cleaned glass substrates. X-ray diffraction patterns of the investigated thin films show that crystallite growth occurs in the orthorhombic phase structure. The surface study carried out by using the scanning electron microscope (SEM) confirms that the grain size increases with gamma irradiation. The optical parameters were estimated from optical transmission spectra data measured from a UV–vis-spectrophotometer in the wavelength range of 200–1100?nm. The refractive index dispersion data of the investigated thin films follow the single oscillator model. The estimated values of static refractive index n₀, oscillator strength E_d, zero frequency dielectric constant ε₀, optical conductivity σ_optical and the dissipation factor increases after irradiation, while the single oscillator energy E_o decreases after irradiation. It was found that the value of the optical band gap of the investigated thin films decreases and the corresponding absorption coefficient increases continuously with an increase in the dose of gamma irradiation. This post irradiation changes in the values of optical band gap and absorption coefficient were interpreted in terms of the bond distribution model.     

Influence of oxygen pressure of ZnO/glass substrate produced by pulsed filtered cathodic vacuum arc deposition

The effects of oxygen pressure on the structural and optical properties of high quality transparent conductive ZnO thin films were studied in detail. ZnO thin films were prepared by pulsed filtered cathodic vacuum arc deposition system under various oxygen pressures on glass substrate at room temperature. With increasing oxygen pressure, the structure and optical properties of films change. The structural and optical properties of the ZnO thin films were investigated using X-ray diffraction, transmittance spectrometry, refractive index, oscillator parameters, energy band gap and Urbach tail. The films show c-axis oriented (0 0 2) hexagonal wurtize crystal structure. It has been found that the grain size of ZnO thin films increases from 16.9 to 22.6 nm with the increase of oxygen pressure from 3.8×10⁻⁴ to 6.9×10⁻⁴ Torr and the crystallinity is enhanced. Average transmittance is about 90% in the visible region of the ZnO thin films. From optical transmittance spectra of ZnO films, the absorption edge shifts towards the taller wavelength with an increase in oxygen pressure. The energy band gap decreases from 3.31 to 3.20 eV with an increase in oxygen pressure. The packing density investigation shows in ZnO films high packing densities (above 0.78) can be obtained.     

金属有机分解法制备的SrTiO3薄膜的光学特性

采用金属有机分解法（MOD）在石英衬底上沉积了SrTiO3薄膜。所制备的薄膜是晶格常数为a=b=c=3.90?的多晶结构。通过测量190—1100nm波段内的透射光谱，采用包络方法计算了薄膜的光学常数（折射率n和消光系数k）。结果表明，采用MOD方法制备的薄膜的折射率大于采用射频磁控溅射、溶胶—凝胶和化学气相沉积方法制备的薄膜的折射率；薄膜的折射率色散关系满足单振子模型，其中振子强度S0为0.88′1014m-2，振子能量E0为6.40eV；薄膜的禁带宽度为3.68eV。     

Synthesis and optical characterization of nanocrystalline CdTe thin films

From several years the study of binary compounds has been intensified in order to find new materials for solar photocells. The development of thin film solar cells is an active area of research at this time. Much attention has been paid to the development of low cost, high efficiency thin film solar cells. CdTe is one of the suitable candidates for the production of thin film solar cells due to its ideal band gap, high absorption coefficient. The present work deals with thickness dependent study of CdTe thin films. Nanocrystalline CdTe bulk powder was synthesized by wet chemical route at pH≈11.2 using cadmium chloride and potassium telluride as starting materials. The product sample was characterized by transmission electron microscope, X-ray diffraction and scanning electron microscope. The structural characteristics studied by X-ray diffraction showed that the films are polycrystalline in nature. CdTe thin films with thickness 40, 60, 80 and 100 nm were prepared on glass substrates by using thermal evaporation onto glass substrate under a vacuum of 10⁻⁶ Torr. The optical constants (absorption coefficient, optical band gap, refractive index, extinction coefficient, real and imaginary part of dielectric constant) of CdTe thin films was studied as a function of photon energy in the wavelength region 400–2000 nm. Analysis of the optical absorption data shows that the rule of direct transitions predominates. It has been found that the absorption coefficient, refractive index (n) and extinction coefficient (k) decreases while the values of optical band gap increase with an increase in thickness from 40 to 100 nm, which can be explained qualitatively by a thickness dependence of the grain size through decrease in grain boundary barrier height with grain size.     

Optical characterization of poly (ethylene oxide)/zinc oxide thin films

The optical characterization of poly (ethylene oxide)/zinc oxide thin films has been done by analyzing the absorption spectra in the spectral wavelength region 380–800 nm using a ultraviolet-spectrophotometer at room temperature. Thin film polymer composites made of poly (ethylene oxide) (PEO) containing zinc oxide (ZnO) filler concentrations (0%, 2%, 6%, 10%, and 14%) by weight were used in this study. The optical results obtained were analyzed in terms of the absorption formula for non-crystalline materials. The optical energy gap and other basic optical constants such as dielectric constants and optical conductivity were investigated and showed a clear dependence on the ZnO filler concentration. It was found that the optical energy gap for the composite films is less than that for the neat PEO, and that it decreases as the ZnO concentration increases. Enhancement of the optical conductivity was observed with increase in the ZnO concentration. Dispersion of refractive index was analyzed using the Wemple–DiDomenico single oscillator model. The refractive index (n), extinction coefficient (k), and dispersion parameters (E_o, E_d) were calculated for the investigated films.     

Optimization of the optical and electrical properties of electron beam evaporated aluminum-doped zinc oxide films for opto-electronic applications

Aluminum-doped zinc oxide (AZO) thin films have been deposited by electron beam evaporation technique on glass substrates. The structural, electrical and optical properties of AZO films have been investigated as a function of annealing temperature. It was observed that the optical properties such as transmittance, reflectance, optical band gap and refractive index of AZO films were strongly affected by annealing temperature. The transmittance values of 84% in the visible region and 97% in the NIR region were obtained for AZO film annealed at 475 °C. The room temperature electrical resistivity of 4.6×10⁻³ Ω cm has been obtained at the same temperature of annealing. It was found that the calculated refractive index has been affected by the packing density of the thin films, whereas, the high annealing temperature gave rise to improve the homogeneity of the films. The single-oscillator model was used to analyze the optical parameters such as the oscillator and dispersion energies.     

Optical parameters in SnO2 nanocrystalline textured films grown on p-InSb (111) substrates

Spectroscopic ellipsometry and photoluminescence (PL) measurements on SnO₂ nanocrystalline textured films grown on p-InSb (111) substrates by using radio-frequency magnetron sputtering at low temperature were carried out to investigate the dependence of the optical parameters on the SnO₂ thin film thickness. As the SnO₂ film thickness increases, while the energy gap of the SnO₂ film decreases, its refractive index increases. The PL spectra show that the broad peaks corresponding to the donor-acceptor pair transitions are dominant and that the peak positions change with the SnO₂ film thickness. These results can help improve understanding for the application of SnO₂ nanocrystalline thin films grown on p-InSb (111) substrates in potential optoelectronic devices based on InSb substrates.     

Optical investigation of vacuum evaporated Se80−xTe20Sbx (x = 0, 6, 12) amorphous thin films

Amorphous thin films of Se_80−xTe₂₀Sb_x (x = 0, 6, 12) chalcogenide glasses has been deposited onto pre-cleaned glass substrate using thermal evaporation technique under a vacuum of 10⁻⁵ Torr. The absorption and transmission spectra of these thin films have been recorded using UV spectrophotometer in the spectral range 400–2500 nm at room temperature. Swanepoel envelope method has been employed to obtain film thickness and optical constants such as refractive index, extinction coefficient and dielectric constant. The optical band gap of the samples has been calculated using Tauc relation. The study reveals that optical band gap decreases on increase in Sb content. This is due to decrease in average single bond energy calculated using chemical bond approach. The values of urbach energy has also been computed to support the above observation. Variation of refractive index has also been studies in terms of wavelength and energy using WDD model and values of single oscillator energy and dispersion energy has been obtained.     

微量Mg掺杂ZnO薄膜的光致发光光谱和带隙变化机理研究

利用射频磁控溅射(RF-MS)法在450℃玻璃基底上制备了Mg掺杂量分别为0.81at%,2.43at%和4.05at%的ZnO薄膜,对其微观结构、室温光致发光光谱(PL)、光学和电学性质进行了研究.结果发现,微量Mg掺杂ZnO薄膜晶体具有六方纤锌矿结构并保持高结晶质量;掺杂0.81at%和2.43at%Mg的ZnO薄膜室温PL谱中近带边发射(NBE)峰的短波方向出现了高能发射带与NBE峰同时存在;随着Mg掺杂量增加至4.05at%,这个高能发射带逐步将NBE峰掩盖.推测在Mg掺杂ZnO薄膜中,Mg2+替代Zn2+附近核外电子的能量增大并产生了一个高能级.而未被Mg2+替代的Zn2+周围的核外电子能量状态不变,带间能级依然存在,随着Mg掺杂量的增加处于高能级的电子数目逐步增加并占绝对优势.因此,ZnO薄膜随着Mg掺杂量增加薄膜禁带宽度增大,这是由于Mg掺杂后周围电子能量增大与Burstein-Moss效应共同作用的结果.另外,薄膜在可见光区域的平均透射率均大于85%,随着Mg掺杂量的增加,薄膜禁带宽度增大并在3.36—3.52eV内变化;Mg掺杂量为0.81at%,2.43at%和4.05at%时,薄膜电阻率分别为2.2×10-3,3.4×10-3和8.1×10-3Ω.cm.     

Optical absorption properties of Ge-Sb-Te films

The optical properties of monolayer Ge2Sb2Te5 thin films with three different thicknesses prepared by dc magnetron sputtering method at the range of 400 - 800 nm were studied. The optical absorption coefficients and the optical energy gap (Eg) were calculated. The results gave values for the absorption coefficients in the range of (1.3 - 7.5) × 105 cm-1 which were in the high absorption wavelength region of 400 - 800 nm. The optical energy gaps were 0.684, 0.753 and 0.810 eV corresponding the films thicknesses of 57, 88 and 127 nm, respectively, showing the characteristic of increasing with the increase of the film thickness.     

Influence of annealing temperature on optical properties of zinc oxide thin films analyzed by spectroscopic ellipsometry method

Zinc oxide (ZnO) thin films were sol–gel spin coated on glass substrates, annealed at various temperatures 300 °C, 400 °C and 500 °C and characterized by spectroscopic ellipsometry method. The optical properties of the films such as transmittance, refractive index, extinction coefficient, dielectric constant and optical band gap energy were determined from ellipsometric data recorded over the spectral range of 300–800 nm. The effect of annealing temperature in air on optical properties of the sol–gel derived ZnO thin films was studied. The transmission values of the annealed films were about 65% within the visible range. The optical band gap of the ZnO thin films were measured between 3.25 eV and 3.45 eV. Also the dispersion parameters such as single oscillator energy and dispersive energy were determined from the transmittance graph using the Wemple and DiDomenico model.     

Optical properties of amorphous HF–In–Zn–O thin films estimated from transmission spectra

Amorphous and flat (<1 nm roughness) Hf–In–Zn–O thin films were prepared by radio frequency (rf) magnetron sputtering method at room temperature (RT) and at 300 °C substrate temperature. The crystal structure and surface morphology were investigated by high resolution X-ray diffraction (HR-XRD) and atomic force microscopy (AFM), respectively. Optical properties of these films were obtained from the UV–VIS–NIR transmission spectra, at normal incidence, over the 200–2000 nm spectral range. Swanepoel's method was used to calculate the thickness and the refractive index of the films. The dispersion of refractive index was obtained in terms of the single-oscillator Wemple–DiDomenico model. The optical absorption edge was described using the direct transition model proposed by Tauc. The film deposited at higher substrate temperature had lower optical band gap, higher refractive index, higher oscillator strength and energy of the effective dispersion oscillator. Optical characterization shows that films become more stable, relaxed and rigid at higher substrate temperature.     

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     

Optical characteristics of transparent samarium oxide thin films deposited by the radio-frequency sputtering technique

Transparent metal oxide thin films of samarium oxide (Sm₂O₃) were prepared on pre-cleaned fused optically flat quartz substrates by radio-frequency (RF) sputtering technique. The as-deposited thin films were annealed at different temperatures (873, 973 and 1073 K) for 4 h in air under normal atmospheric pressure. The topological morphology of the film surface was characterized by using atomic force microscopy (AFM). The optical properties of the as-prepared and annealed thin films were studied using their reflectance and transmittance spectra at nearly normal incident light. The estimated direct optical band gap energy (\(E_{\mathrm {g}}^{\mathrm {d}}\)) values were found to increase by increasing the annealing temperatures. The dispersion curves of the refractive index of Sm₂O₃ thin films were found to obey the single oscillator model.     

Optical constants of Na-doped ZnO thin films by sol-gel method

The structural and optical properties of pure and Na-doped ZnO thin films have been investigated by X-ray diffraction (XRD), atom force microscopy and UV-Vis spectrophotometer. The crystal structure of all the thin films is the hexagonal wurtzite. The average grain size and surface roughness increases with the increase of the Na/Zn ratio. The optical band gap of the thin films decreases from 3.26 to 3.12 eV by increasing the Na/Zn ratio from 0.0 to 0.10. Transmittance spectra were used to determine the optical constants of the thin films, and the effect of Na/Zn ratio on the optical constants was investigated. With the increase of Na/Zn ratio, the refractive index decreases and the extinction coefficient increases in the 380-700 nm spectral range.     

Fe掺杂对CdS光学特性的影响

采用低压金属有机化学气相沉积技术,在固定源流量的条件下,通过调节衬底温度(270~360℃)生长了不同Fe掺杂浓度的CdS薄膜。光谱测量表明低铁掺杂对CdS晶格振动的影响较小,但对光致发光性质影响较为明显。样品的光致发光谱包括两部分:2.5eV附近带-带跃迁的发光以及2.0~2.4eV之间与缺陷相关的发光。随着铁含量的增加,带-带跃迁逐渐被抑制,发光光谱被缺陷相关的发光主导,同时薄膜的电导也由n型转为p型,说明Fe离子掺入在薄膜引入了受主杂质。通过不同激发密度下的光致发光光谱测量,我们将2.0~2.4eV的发光归结为铁受主相关的D-A对发射,并根据掺杂浓度和发光峰位置估算了Fe受主的能级位置。     

退火对磁控溅射HfSi_xO_y薄膜光学性质的影响

采用射频反应磁控溅射方法在硅衬底制备了HfSixOy薄膜,用X射线光电子能谱(XPS)分析了HfSixOy薄膜的成分,用X射线衍射(XRD)检测了薄膜的结构,并用椭圆偏振光谱仪研究了退火处理对薄膜光学性质的影响。XRD谱显示,HfSixOy薄膜经700℃高温退火处理后仍为非晶态,而在900℃高温退火处理后出现晶化。采用Tauc-Lorentz(TL)色散模型对测试得到的曲线进行拟合并分析得出薄膜的光学常数,结果表明,薄膜的折射率随退火温度的升高而增加,而消光系数随退火温度的升高呈降低趋势。薄膜的光学带隙随着退火温度的升高增加,采用外推法得到薄膜沉积态和经500℃,700℃,900℃退火后的带隙分别为5.62,5.65,5.68,5.98eV。