Electronic,optical and bonding properties of MgYZ2 (Y=Si,Ge; Z=N,P) chalcopyrites from first principles

The electronic and optical properties of MgYZ₂ (Y=Si, Ge; Z=N, P) compounds are carried out using first-principle calculations within the density functional theory. The calculations show close correspondence to the available experimental data compared to the previous theoretical calculations. Band gap decreases by changing the cations Y from Si to Ge as well as Z from N to P in MgYZ₂. The N/P p-states contribute majorly in the density of states. Bonding nature of the herein studied compounds is predicted from the electron density plots. Optical response of these compounds is noted from the complex refractive index, reflectivity and optical conductivity. The direct band gap and the high reflectivity of these compounds in the visible and ultraviolet regions of electromagnetic energy spectrum ensure their applications in optoelectronic and photonic domains.     

Effect of the film thickness on the optical constants and dispersion parameters of chalcogenide Ge20Se70Ag10 thin film

Chalcogenide thin films of Ge₂₀Se₇₀Ag₁₀ of thicknesses 150, 300 and 450 nm are prepared by a thermal evaporation technique. The crystalline phases of the deposited film are identified by X-ray diffraction. The transmittance and reflectance of the films are measured in the wavelength range 200–2500 nm. The optical band gap decreases while the width of the localized states tail increases with increasing film thickness. Variation of refractive index and extinction coefficient with the film thickness is studied to analyze the optical efficiency of these films. Application of the single oscillator model to the films reveals that the oscillator energy decreases while the dispersion energy increases with increasing thickness. The variation of the optical constants suggests that the thickness change is a good choice to control the optical properties of Ge₂₀Se₇₀Ag₁₀ film.     

使用椭偏光谱研究氮化铝薄膜在不同温度下的光学性质

通过椭偏仪对生长在蓝宝石上的不同厚度氮化铝薄膜的变温光学性质进行了研究, 并采用托克-洛伦兹模型对椭偏实验数据进行了拟合分析, 精确得到了氮化铝薄膜的厚度和光学常数(折射率n, 消光系数k)等.研究的结果表明: 相比薄的氮化铝薄膜, 厚的氮化铝薄膜的折射率较大.随着温度的升高, 氮化铝的折射率、消光系数和带隙会向低能端单调地移动(红移);厚度对带隙随温度改变的影响较小, 对折射率则有一定的影响.     

一种新型溶胶-凝胶方法制备ZnO薄膜的椭圆偏振光谱研究

使用一种新型的溶胶．凝胶方法制备了ZnO薄膜,此方法的特点在于操作简单、无毒、实用。此方法可在非单晶基片（如玻璃、石英等）上制备最大晶粒尺寸大于100nm的大面积ZnO薄膜。利用椭圆偏振光谱观察到了所制备ZnO薄膜折射率随光子能量的增加在光子能量等于禁带宽度处出现峰值的现象;计算了ZnO薄膜的光学带隙;证明了ZnO薄膜中存在由氧空位和锌间隙原子在带隙中引入的缺陷能级。     

Structural,optical and dielectric properties of HfSiO films prepared by co-evaporation method

HfSiO dielectric films were prepared on Si substrate by the co-evaporation method. The chemical composition, crystalline temperature, optical and electrical properties of the compound film were investigated. X-ray photoelectron spectroscopy analysis illustrated that the atom ratio of Hf to Si was about 4:1 and Hf–Si–O bonds appeared in the film. The X-ray diffraction analysis revealed that the crystalline temperature of the film was higher than 850 °C. Optical measurements showed that the refractive index was 1.82 at 550 nm wavelengths and the optical band gap was about 5.88 eV. Electrical measurements demonstrated that the dielectric constant and a fixed charge density were 18.1 and 1.95×10¹² cm⁻² respectively. In addition, an improved leakage current of 7.81 μA/cm² at the gate bias of −3 V was achieved for the annealed HfSiO film.     

Investigation of optical and chemical bond properties of hydrogenated amorphous silicon nitride for optoelectronics applications

The aim of this work is to determine optimal deposition parameters of silicon nitride for optical applications. The authors present the investigation of hydrogenated amorphous silicon nitride SiN_x:H deposited by the low temperature PECVD method in high frequency reactors. The study of hydrogen bonds in the SiN_x:H thin films were detailed. The impact of NH₃, SiH₄ and N₂ flow ratio and radio frequency power on optical coefficients in relation to chemical composition and roughness of the film is studied. The correlation between chemical bonds (N–H, Si–H) and refractive index and extinction coefficients is systematically verified. The experimental results show that the films with high refractive indexes superior to 2.05 and low roughness of about 0.35 nm can be achieved for optoelectronics applications by tuning the flow ratio or decreasing the RF power. A variety of processes have been suggested as compatible with low thermal budget (under 350 °C) in order to integrate optical waveguides with lower loss. In particular, the incorporation of N₂ as dilution gas is suited to the fabrication of SiN_x:H films optical waveguide requiring low N–H bonds, low concentration of hydrogen [H] and high refractive index.     

离子束溅射宽带吸收薄膜设计与制备技术研究

Si薄膜在可见光和近红外波段具有一定的吸收特性,可用于宽带吸收薄膜的制备。采用离子束溅射技术,在熔融石英基底上制备了不同沉积工艺参数的Si薄膜,基于透、反射光谱和椭偏光谱的全光谱数值拟合法,计算了Si薄膜的光学常数,并研究了氧气、氮气流量对其光学特性的影响。选择Si和Ta2O5作为高折射率材料、SiO2作为低折射率,设计了吸收率为2%和10%的宽带（1 000~1 400 nm）吸收薄膜。采用离子束溅射沉积技术,在熔融石英基底上制备了宽带吸收薄膜,对于A=2%的宽带吸收光谱,在1 064、1 200、1 319 nm的吸收率分别为2.12%、2.15%和2.22%;对于A=10%的宽带吸收光谱,在1 064、1 200、1 319 nm的吸收率分别为9.71%、8.35%和9.07%。研究结果对于吸收测量仪、光谱测试仪等仪器的定标具有重要的作用。     

Deposition and characterization of Si-rich silicon oxide films using HMDS for integrated photonics

Silicon-rich silicon oxide (SRSO) films were deposited using thermal-CVD system with organic precursor hexamethyldisilazane (HMDS) and oxygen (O₂) at the temperature range of 760–820 °C. The deposited SRSO films were characterized by using ellipsometry, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray (EDAX). The effect of deposition temperature on the physical and optical properties of deposited SRSO films has been studied and analyzed. It has been observed that the refractive index (RI) of the deposited films increases while the stress of compressive nature decreases with the corresponding increase in deposition temperature. The peak positions of Si–O–Si stretching bond and the full-width at half maxima (FWHM) of these peaks have been investigated by using FTIR spectroscopy. It was found that the peak position of Si–O–Si stretching bond move toward lower wave number while the corresponding FWHM increases with increase in the deposition temperature. The peak intensities of Si–H, O–H and Si–OH bonds decrease with corresponding increase in deposition temperature, which signifies an improvement in the quality of the deposited SRSO films. The SEM and EDAX analysis clearly reveals the successful deposition of SRSO films with some dense clusters of silicon having size about 500 nm on the surface of the deposited films.     

Plasma-assisted chemical vapor deposited silicon oxynitride as an alternative material for gate dielectric in MOS devices

Silicon oxynitride films have been deposited on Si substrates at 200 °C by a remote-plasma-assisted process in a RF-plasma CVD reactor using Si(OC₂H₅)₄ (TEOS) as a precursor and nitrogen as gas ambient. During deposition the Si substrates were biased with negative voltages of −120 and −600 V or were under no DC bias and the influence of this voltage on the film properties has been considered. Film parameters, such as density, chemical bonds, refractive index, composition, oxide and interface charge densities of the deposited dielectric films have been estimated by analysis of the results from the infrared (IR) spectroscopy, spectral ellipsometry (SE) and capacitance-voltage (C-V) measurements. The IR and SE results have proven the films are oxynitrides of silicon with predominantly oxide network. The analysis of the capacitance-voltage characteristics has shown that the dielectric charge densities increase with increasing DC bias but they remain considerably low in comparison to that for a standard SiO₂/Si structure before any annealing steps.     

Low-Temperature deposition of dielectric films by microwave plasma enhanced decomposition of hexamethyldisilazane

Hexamethyldisilazane (HMDS) has been used as an organosilicon source for the deposition of dielectric films at low temperatures (200-250° C) by microwave plasma enhanced CVD technique. Hydrogenated films of variable composition of silicon carbonitride, silicon oxynitride and silicon dioxide have been deposited by decomposition of HMDS in the presence of additive gases like NH₃, O₂ and H₂ under different process conditions. Deposited films have been characterized by the measurement of refractive index and buffered HF etch rate, and by the analysis of XPS and infrared transmission spectra. An increase in HMDS partial pressure generally results in the decrease of refractive index. The films show stable C-V characteristics of metal-insulator-semicon-ductor (MIS) capacitors with positive insulator charge density.     

Atomistic origin of high-quality “novel SiON gate dielectrics”

We have investigated the effect of the oxygen incorporation into SiN films by the first principles calculations. The calculated results show that the oxygen incorporation tends to generate defect states in SiN band gap by forming dangling bonds and floating bonds of Si. Based on the calculated results, it is also indicated that the high quality SiON film can be fabricated by suppressing the incorporation of O atoms into the SiN film, reproducing the reported experiments.     

纳米硅薄膜光学性质的测定与研究

通过测定纳米硅薄膜的透射谱,建立计算模型计算得出薄膜样品的折射率、厚度、吸收系数和光能隙.计算结果表明这种半导体材料在620 nm波长附近的折射率约为3.4,计算得到的厚度与用台阶仪测量的结果吻合很好.在620 nm波长附近的吸收系数介于吸收系数较小的晶体硅与吸收系数较大的非晶硅之间,光能隙约为1.6 eV,两者都随晶态含量增大而呈减小趋势.     

Optical and electrical characterization of the electron beam gun evaporated TiO2 film

We report measured evolutions of the optical band gap, refractive index and relative dielectric constant of TiO₂ films obtained by electron beam gun evaporation and annealed in an oxygen environment. A negative shift of the flat band voltage with increasing annealing temperatures, for any film thickness, is observed. A dramatic reduction of the leakage current by about four orders of magnitude to 5×10⁻⁶ A cm⁻² (at 1 MV cm⁻¹) after 700°C and 60 min annealing is found for films thinner than 15 nm. The basic carrier transport mechanisms at different ranges of applied voltage such as hopping, space charge limited current and Fowler–Nordheim is established. An equivalent SiO₂ thickness in order of 3.5 nm is demonstrated.     

Effect of Film Thickness on Properties of a-Si∶H Films

The a-Si∶H films with different thickness smaller than 1 μm were deposited by plasma enhanced chemical vapor deposition (PECVD) under the optimum deposition conditions. The effect of different thickness on film properties is analyzed.The results show that,with the increase of the film thickness,the dark conductivity, photoconductivity and threshold voltage increase, the optical gap and peak ratio of TA to TO in the Raman spectra decrease, the refractive index keeps almost constant, and the optical absorption coefficient and current ratio of on/off state first maximize and then reduce.     

Optical and mechanical properties of C,Si, Ge,and 3C–SiC determined by first-principles theory using Heyd–Scuseria–Ernzerhof functional

Accurately calculating the band gap and electronic state density distribution of crystals is significant in determining optical properties. First-principles calculations were based on the projector-augmented-wave method with the Perdew–Burke–Ernzerhof generalized gradient approximation functional, pure density functional theory (DFT) and Heyd–Scuseria–Ernzerhof (HSE) hybrid functional. Such calculations account for the lattice parameters, electronic structure, optical properties, and mechanical properties of materials, which include the diamond-C and zinc blende structure of Si, Ge, and 3C–SiC in this study. The results obtained with HSE calculations is more accurate than that of the pure DFT calculations, and consistent with previous experimental values. The band structure and density of states of Si, Ge, and 3C–SiC indicate that these materials are indirect band gap materials. Based on HSE calculation, the band gap of Si and 3C–SiC is in accordance with previous experimental values. The imaginary part of the analytical dielectric function, the refractive index, and the adsorption coefficient also matches previous experimental values. A corresponding relationship exists among the peak of the imaginary part of the analytical dielectric function, the refractive index, and the adsorption coefficient. The optical properties have a direct relationship with the distribution of the crystal band gap and electronic state density. The materials exhibit brittleness. Although 3C–SiC is not as hard and stiff as diamond, it is a better semiconductor than Si and Ge. The mechanical anisotropy of the four materials is inconspicuous. The anisotropy of diamond-C in terms of its Young's modulus is extremely inconspicuous.     

锰掺杂对钛酸锶铅铁电薄膜带-带跃迁和带尾吸收特性的影响

通过透射光谱研究了锰掺杂量对钛酸锶铅铁电薄膜光学特性尤其是带-带跃迁和带尾吸收特性的影响,并利用柯西色散关系获得了光学透明区的光学常数.研究表明:随着锰掺杂量的增加,钛酸锶铅铁电薄膜的禁带宽度减小而带尾能增加.禁带宽度随锰掺杂的收缩可以归因为锰3d轨道降低了导带底的能级及掺杂后晶格的减小.掺杂锰离子的随机占位和非等价掺杂后氧空位浓度的增加则是导致局域带尾态拓宽的主要原因.     

8 MeV electron beam induced modifications in the structural,optical and electrical properties of Al doped ZnO thin film

The influence of high energy (8 MeV) electron irradiation, with different dose rates (0 kGy, 1 kGy, 5 kGy, 10 kGy), on the structural, optical and electrical properties of sol-gel spin coated Al-doped ZnO (AZO) thin films have been studied. The X-ray diffraction curve displays the coating of c-axis oriented films under the state of compressive stress. A further analysis reveals that the interstitial sites were occupied by the Al in AZO upon electron irradiation. With the increase in irradiation dose, the energy gap of the film shows a redshift due to the enhanced localized states in the band structure. An increment in the values of refractive index of the films after irradiation is attributed to their enhanced optical density. Steady state luminescence spectra reveal the presence of zinc interstitial and oxygen interstitial defects in the irradiated film. Time-resolved photoluminescence (PL) measurement shows that the dominant defect related recombination mechanism in the irradiated films is arising due to the increased dangling bonds and defect related transitions. The increase in sheet resistance upon electron irradiation is attributed to decreasing carrier concentration in the film. The irradiated AZO film may be useful for space applications and in the radiation environment.     

Synthesis,Optical and Photoluminescence Properties of Cu-Doped Zno Nano-Fibers Thin Films: Nonlinear Optics

Different concentrations of copper-doped zinc oxide thin films were coated on a glass substrate by sol–gel/spin-coating technique. The structural properties of pure and Cu-doped ZnO films were characterized by different techniques, i.e., atomic force microscopy (AFM), photoluminescence and UV–Vis-NIR spectroscopy. The AFM study revealed that pure and doped ZnO films are formed as nano-fibers with a granular structure. The photoluminescence spectra of these films showed a strong ultraviolet emission peak centered at 392 nm and a strong blue emission peak cantered at 450 nm. The optical band gap of the pure and copper-doped ZnO thin films calculated from optical transmission spectra (3.29–3.23 eV) were found to be increasing with increasing copper doping concentration. The refractive index dispersion curve of pure and Cu-doped ZnO film obeyed the single-oscillator model. The optical dispersion parameters such as E _o , E _d , and \(n_{{\infty }}^{2}\) were calculated. Further, the nonlinear refractive index and nonlinear optical susceptibility were also calculated and interpreted.     

a-Si:C:H and a-Si:N:H Thin Films Obtained by PECVD for Applications in Silicon Solar Cells

Hydrogenated amorphous silicon-carbon (a-Si:C:H) and hydrogenated silicon-nitrogen (a-Si:N:H) antireflective films were deposited by plasma-enhanced chemical vapor deposition (PECVD) at 13.56 MHz in SiH₄ + CH₄ and SiH₄ + NH₃ gaseous mixtures of various compositions. The silicon and glass samples were investigated by optical spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). A correlation between film properties and process parameters was found. The refractive index decreased and the energy gap increased with an increase of carbon and nitrogen in the films. For some process parameters, it was possible to obtain smooth, hydrogen rich, and homogeneous films of low reflectivity. The silicon solar cells with antireflective coatings revealed an increase in efficiency.     

Analysis of Optical properties of nanocrystalline titanium dioxide films

The optical properties of materials can be characterized in terms of the complex refractive index. We developed a simple and efficient method for determining the complex refractive index of nanomaterials that uses the relationship between this parameter and the light spectrum measured for a specimen. The optical properties of nanoparticle and nanotube TiO₂ films were investigated. The results show that the morphology of nano-TiO₂ affects the complex refractive index spectrum and therefore influences light dispersion and absorption of the film. We also simulated the optical energy density distribution within equivalent plane films using complex refractive index data.