First principle study of the structural and optoelectronic properties of cubic perovskites CsPbM3 (M=Cl, Br, I)

The highly accurate all electrons full potential linearized augmented plane wave method is used to calculate structural, electronic, and optical properties of cubic perovskites CsPbM₃ (M=Cl, Br, I). The theoretically calculated lattice constants are found to be in good agreement with the experimentally measured values. It is found that all of these compounds are wide and direct bandgap semiconductors with bandgap located at R-symmetry point, while the bandgap decreases from Cl to I. The electron densities reveal strong ionic bonding between Cs and halides but strong covalent bonding between Pb and halides. Optical properties of these compounds like real and imaginary parts of dielectric functions, refractive indices, extinction coefficients, reflectivities, optical conductivities, and absorption coefficients are also calculated. The direct bandgap nature and high absorption power of these compounds in the visible-ultraviolet energy range imply that these perovskites can be used in optical and optoelectronic devices working in this range of the spectrum.     

Temperature profile of the multilayer structure irradiated by pulsed laser

Two programs are developed to calculate the temperature profile, as well as the reflectance, transmittance and absorption of a given multilayer film structure, in order to better understand the laser energy distribution between the reflectance, transmittance and absorption in each film layer. An inorganic Blu-ray recordable disc (BD-R) structure is used as a practical demonstration of the multilayer structure. The reflectance and absorption of the BD-R structure exhibit opposite trends and oscillate repeatedly with varying lower or upper dielectric layer thickness while the rest of the film thickness remains unchanged. The energy absorption in an absorbed layer depends on the thickness of the dielectric layers, its relative position in the structure and the extinction coefficient of its optical constant. The total absorption ratio of its maximum to minimum can be over 3 when changing the lower dielectric layer thickness of the studied structure. The layer thickness acts as an energy valve to control the energy flow into the multilayer structure. The thermal profile of the multilayer film structure irradiated by a pulsed laser is calculated at different positions in the film layers with time. The calculated temperatures in the recording alloy layer exhibit linear relationship with the applied power level. The effect of the laser duration time on the temperature increase in the recording layer is significant in the first few nanoseconds and becomes saturated if the heat balance is established in the structure. The calculated temperature is consistent with the experimental recording result when the structure is recorded at 4-time BD-R recording speed.     

Electronic and optical properties of layered chalcogenide FeIn2Se4

We investigated the spectral-dependent dielectric function and temperature-dependent bandgap energy of layered chalcogenide FeIn₂Se₄ crystals. The critical-point energy and Lorentzian broadening were analyzed by fitting second-derivative spectra using the standard critical point model. The temperature effect of the bandgap energy was analyzed based on an analytical model considering both thermal lattice expansion and electron–phonon interactions. We also extensively analyzed the temperature dependence of absorption tails and identified their possible origins. The dielectric functions and absorption coefficient in the photon-energy range of 0.75–4.75 eV were obtained. The results also showed that optical phonon modes associated with the electron–phonon interactions could be closely related to the average phonon energy.     

Ce掺杂CrSi2电子结构和光学性质的第一性原理研究

采用基于密度泛函理论的第一性原理计算方法,对未掺杂及Ce掺杂CrSi2的电子结构和光学性质进行理论计算。计算结果表明,未掺杂CrSi2是间接带隙半导体,其禁带宽度为0.392 eV,掺杂Ce元素,仍然是间接半导体,带隙宽度下降为0.031eV。未掺杂CrSi2在费米能级附近主要由Cr-5d、Si-3p态贡献。Ce掺杂后在费米能级附近主要由Cr-5d轨道,Ce-4f轨道,C-2p,Si-3p轨道贡献,掺杂后电导率提高。未掺杂CrSi2有两个介电峰,掺杂后,只有一个介电峰。未掺杂CrSi2,在能量为6.008处吸收系数达到最大值,掺杂后在能量为5.009eV处,吸收系数达到最大值。     

Ta掺杂对ZnO光电材料性能影响的研究

采用基于密度泛函理论第一性原理的方法, 研究了Ta掺杂ZnO的电子结构和光学性质. 计算结果表明: 掺入Ta原子后, 费米能级进入导带, 随着掺杂浓度的增加, 带隙逐渐变窄, 介电函数虚部、吸收系数、反射率和折射率均发生明显变化, 介电函数虚部和反射率均向高能方向移动, 吸收边发生红移, 从理论上指出了光学性质和电子结构的内在联系.     

Compact and broadband waveguide taper based on partial bandgap photonic crystals

Partial bandgap characteristics of parallelogram lattice photonic crystals are proposed to suppress the radiation modes in a compact dielectric waveguide taper so as to obtain high transmittance in a large wavelength range. Band structure of the photonic crystals shows that there exists a partial bandgap, The photonie crystals with partial bandgap are then used as the cladding of a waveguide taper to reduce the radiation loss efficiently. In comparison with the conventional dielectric taper and the complete bandgap photonic crystal taper, the partial bandgap photonic crystal taper has a high transmittance of above 85% with a wide band of 170 nm.     

掺杂Si/SiO_2界面电子结构与光学性质的第一性原理研究

采用基于密度泛函理论的第一性原理方法,在局域密度近似(LDA)下研究了B掺杂Si/SiO_2界面及其在压强作用下的电子结构和光学性质.能带的计算结果表明:掺杂前后Si/SiO_2界面均属于直隙半导体材料,但掺B后界面带隙由0. 74 eV减小为0. 57 eV,说明掺B使材料的金属性增强;对B掺杂Si/SiO_2界面施加正压强,发现随着压强不断增大,Si/SiO_2界面的带隙呈现了逐渐减小的趋势,并且由直隙逐渐转变为间隙.光学性质的计算结果表明:掺B对Si/SiO_2界面在低能区(即红外区)的介电函数虚部、吸收系数、折射率以及反射率等光学参数有显著影响,且在红外区出现新的吸收峰;对B掺杂Si/SiO_2界面施加正压强,随着压强增大,红外区的吸收峰逐渐消失,而在紫外区出现了吸收峰.上述结果表明,对Si/SiO_2界面掺B及施加正压强均可调控Si/SiO_2界面的电子结构与光学性质.本文的研究为基于Si/SiO_2界面的光电器件研究与设计提供一定的理论参考.     

室温下表面极化效应对量子点带隙和吸收峰波长的影响

对于离散在本底介质中的纳米晶体量子点,考虑表面极化效应,通过像电荷法建立极化势能项,应用微扰法求解激子的薛定谔方程,得到了与本底介电系数直接相关的量子点带隙解析表达式.对不同本底中尺寸依赖的量子点带隙、第一吸收峰波长、第一吸收峰波长移动进行的计算表明,表面极化效应对量子点的带隙和第一吸收峰波长有明显的影响.随着本底介电系数的增大,量子点的带隙减小,第一吸收峰波长红移.量子点在不同本底中的第一吸收峰波长移动会在某个固定粒径达到最大值,最大值对应的粒径取决于量子点种类.     

Fe掺杂GaN光电特性的第一性原理研究

基于密度泛函理论体系,计算了本征GaN材料和12.5%的Fe掺杂GaN体系的光电特性,分析了晶体结构、能带结构和电子态分布、介电函数、吸收系数、折射率、反射率、能量损失谱和消光系数,从理论上讨论了掺杂对体系光电特性的影响.计算所得理想GaN的禁带宽度为3.41 eV,Fe的重掺杂体系明显变窄,为3.06 eV,但仍为直接带隙半导体.本征GaN材料与Fe掺杂GaN体系的静态介电常数为5.74和6.20,折射率为2.39和2.48,能量损失最大值在20.02 eV和18.96 eV,最大吸收系数能量均在13.80 eV左右.计算结果为Fe掺杂GaN高压光电导开关材料及器件的进一步研究提供了有力的理论依据和实验支持.     

Effect of anomalous transmittance in EUV multilayer optics

In this paper the effect of anomalous transmittance in the EUV spectral region is considered theoretically. The effect consists in a resonant enhancement of the transmittance of a periodic multilayer structure compared with that of a uniform film. The physical reason of the effect lies in the fact that the minima of the wave field intensity of a certain wavelength are placed just in the center of thin absorbing layers resulting in a resonant decrease of wave absorption. The condition of this appearance is analyzed: it is necessary the absorption coefficient (imaginary part of the dielectric constant) of two materials composing a multilayer structure to differ by a factor of 10, at least. A possibility of the use of a multilayer filter in metrology of broadband EUV sources is discussed.     

The relationship between refractive index-energy gap and the film thickness effect on the characteristic parameters of CdSe thin films

CdSe thin films were deposited on glass substrates using Successive Ionic Layer Adsorption and Reaction (SILAR) method at room temperature and ambient pressure. The relationship between refractive index and energy bandgap was investigated. The film thickness effect on the structural, morphological, optical and electrical properties of CdSe thin films was investigated. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies showed that all the films exhibit polycrystalline nature with hexagonal structure and are covered well with glass substrates. The crystalline and surface properties of the films improved with increasing film thickness. The optical absorption studies revealed that the films are found to be a direct allowed transition. The energy bandgap values were changed from 1.93 to 1.87 eV depending on the film thickness. The electron effective mass (m_e^?/m_o), refractive index (n), optical static and high frequency dielectric constant (ε_o, ε_∞) values were calculated by using the energy bandgap values as a function of the film thickness. The resistivity of the films changed between 10⁶ and 10² Ω-cm with increasing film thickness at room temperature.     

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.     

第一性原理研究[112]硅锗异质结纳米线的电子结构与光学性质

基于密度泛函理论体系下的广义梯度近似,本文利用第一性原理方法着重研究了[112]晶向硅锗异质结纳米线的电子结构与光学性质.能带结构计算表明:随着锗原子数的增加,[112]晶向硅锗纳米线的带隙逐渐减小;对Si_(36)Ge_(24)H_(32)纳米线施加单轴应变,其能量带隙随拉应变的增加而单调减小.光学性质计算则表明:随着锗原子数的增加,[112]硅锗纳米线介电函数的峰位和吸收谱的吸收边均向低能量区移动;而随着拉应变的增大,吸收系数峰值呈现出逐渐减小的趋势,且峰位不断向低能量区移动,上述结果说明锗原子数的增加与施加拉应变均导致[112]硅锗纳米线的吸收谱产生红移.本文的研究为硅锗异质结纳米线光电器件研究与设计提供一定的理论参考.     

膜厚对射频磁控溅射法制备的SnS薄膜结构和光学性质的影响

利用射频磁控溅射法在玻璃衬底上制备SnS薄膜,用X射线衍射(XRD)、能谱仪(EDS)、原子力显微镜(AFM)、场发射扫描电镜(FE-SEM)和紫外-可见-近红外分光光度计(UV-Vis-NIR)分别对所制备的薄膜晶体结构、组分、表面形貌、厚度、反射率和透过率进行表征分析。研究结果表明:薄膜厚度的增加有利于改善薄膜的结晶质量和组分配比,晶粒尺寸和颗粒尺寸随着厚度的增加而变大。样品的折射率在1 500~2 500 nm波长范围内随着薄膜厚度的增加而增大。样品在可见光区域吸收强烈,吸收系数达10⁵ cm^-1量级。禁带宽度在薄膜厚度增加到1 042 nm时为1.57 eV,接近于太阳电池材料的的最佳光学带隙(1.5 eV)。     

应变对纤锌矿结构GaN电子结构及光学性质的影响

使用第一性原理密度泛函理论（DFT）框架下的广义梯度近似（GGA+U）方法计算单轴应变对纤锌矿结构GaN的键长、差分电荷密度、电子结构以及光学性质的影响.结果表明：带隙随应变的增加而减小,压应变在（-1%~-3%）范围内变化时带隙变化不明显,压应变超过3%时带隙随应变的增大显著减小.光学性质研究表明,应变对介电函数虚部峰的位置和大小都产生影响,静态介电常数随应变的增大而增大;应变使GaN的吸收系数减小.     

Structural and optical properties of thermally evaporated 2-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitrophenyl)acetonitrile thin films

The structural and optical properties of as-deposited and γ-rays irradiated 2-(2,3-dihydro-1,5dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitrophenyl)acetonitrile (DOPNA) thin films have been reported. The structural properties of as-deposited and γ-rays irradiated DOPNA thin films are characterized by Fourier transformation infrared, X-ray diffraction and transmission electron microscope techniques. The transmittance, T(λ), and reflectance, R(λ), are measured at the normal incidence of light by a double beam spectrophotometer in the wavelength range 200-2200 nm. The refractive and absorption indices have been calculated. The dispersion parameters such as dispersion energy, oscillator energy and dielectric constant at high frequency are evaluated. The data of the absorption coefficient are analyzed in order to determine the type of inter-band electronic transitions and the optical band gap of the films. Other optical absorption parameters, namely, the extinction molar coefficient, oscillator strength and the electric dipole strength, are also calculated.     

La掺杂3C-SiC电子结构和光学性质的第一性原理研究

采用基于密度泛函理论的第一性原理计算方法,对未掺杂及稀土材料La掺杂3C-SiC的电子结构和光学性质进行理论计算.计算结果表明,La掺杂引起3C-SiC晶格体积增大,掺杂体系能量更小,掺杂体系的结构更稳定;未掺杂3C-SiC是直接带隙半导体,其禁带宽度为1.406 eV,La掺杂后带隙宽度下降为1.161 eV,La掺杂3C-SiC引入了3条杂质能级,能量较高的1条杂质能级与费米能级发生交叠,另外2条杂质能级都在费米能级以下价带顶之上,La掺杂引起3C-SiC吸收谱往低能区移动,未掺杂3C-SiC的静态介电常数为2.66,La掺杂引起静态介电常数增加为406.01,La掺杂3C-SiC是负介电半导体材料.     

New calibration method for UV-VIS photothermal deflection spectroscopy set-up

Photothermal deflection spectroscopy has emerged as a useful technique for the determination of the absorption of materials with a small absorption coefficient. The technique offers relative values of the material absorptivity and, therefore, requires a calibration procedure in order to determine the absolute values. In this work, we present a new calibration method for a photothermal deflection spectroscopy set-up working in the UV-VIS, spectral range. The method is based on the use of reference samples with different levels of absorption. The samples, consisting of single thin films of amorphous carbon on transparent substrates, are optically characterized by means of spectrophotometric measurements. The accurate characterization of the samples enables the computation of their corresponding optical absorptivity in the PDS set-up. The calibration method is cross-checked by comparison of the measurements for the different reference samples and is finally applied to the study of the absorption of dielectric films in the UV.     

稀土元素(Ce,Pr)掺杂GaN的电子结构和光学性质的理论研究

采用基于密度泛函理论的第一性原理平面波赝势法计算了稀土元素Ce,Pr掺杂GaN的晶格参数、能带、电子态密度和光学性质,使用LSDA +U的方法处理具有强关联作用的稀土4f态,并分析比较计算结果.计算表明:掺入Ce和Pr后的体系相比未掺杂的GaN晶格常数增大,带隙变窄,并分别在禁带中和价带顶附近引入了局域的杂质能级,该能级主要由Ce和Pr的4f电子提供;掺杂后都发生了磁有序化并产生磁矩;最后定性分析了掺杂前后介电函数和光吸收系数的变化,掺Ce的体系在介电函数和吸收系数的低能区出现了峰值,该峰的出现和禁带中的杂质能级到导带底的跃迁有关,而掺Pr的体系由于带隙变窄使介电峰和吸收边发生红移.     

First Principle Study on Optical Properties of Tri-Group Doped(6,6) SiC Nanotubes

The optical properties of tri-group(B, Al, Ga, In) doped(6,6) SiC nanotubes(SiCNTs) are studied from first principles. The results show that the main absorption and dispersion of SiCNTs caused by the intrinsic transition appear in the ultraviolet-visible region(below 500 nm), and the tri-group doping increases the minimum dielectric constant value resulting in enhanced transmittance. In addition, the tri-group doping can introduce a weak absorption and dispersion region in the near-mid-infrared region, and the response peak blue shifts as the diameter of the doping atom increases. Comparative studies of reflectance, absorptivity, and transmittance show that the key factors affecting the transmittance of SiCNTs are reflectance(or refractive index) rather than absorption coefficient.