Electronic structures and optical properties of Nb-doped SrTiO3 from first principles

The n-type Nb-doped SrTiO₃ with different doping concentrations were studied by first principles calculations. The effects of Nb concentration on the formation enthalpy, electronic structure and optical property were investigated. Results show that Nb preferentially enters the Ti site in SrTiO₃, which is in good agreement with the experimental observation. The Fermi level of Nb-doped SrTiO₃ moves into the bottom of the conduction band, and the system becomes an n-type semiconductor. The effect of Nb-doping concentration on the conductivity was discussed from the microscopic point of view. Furthermore, the 1.11 at% Nb-doped SrTiO₃ shows strong absorption in the visible light and becomes a very useful material for photo-catalytic activity. The 1.67 at% and 2.5 at% Nb-doped models will be potential transparent conductive materials.     

ZnS:Er电子结构和光学性质的第一性原理计算

采用第一性原理平面波赝势方法,分析了ZnS及掺杂Er3+之后的电子结构,进而预测了其光学性质。结果表明,掺杂之后体系的带隙变窄,同时价带与导带之间形成一个新的中间带。随着掺杂Er3+浓度的增加,体系的绝缘性呈下降趋势,吸收光谱则发生红移现象。这一结论与前人报道的实验结果相符。     

含空位缺陷碳化硅纳米管的电子结构和光学性质

Based on first-principle calculations,the electronic structures and optical properties of a single-walled (7,0) SiC nanotube(SiCNT) with a carbon vacancy defect or a silicon vacancy defect are investigated.In the three silicon atoms around the carbon vacancy,two atoms form a stable bond and the other is a dangling bond.A similar structure is found in the nanotube with a silicon vacancy.A carbon vacancy results in a defect level near the top of the valence band,while a silicon vacancy leads to the formation of three defect levels in the band gap of the nanotube.Transitions between defect levels and energy levels near the bottom of the conduction band have a close relationship with the formation of the novel dielectric peaks in the lower energy range of the dielectric function.     

Electronic band structures and optical properties of atomically thin AuSe: first-principle calculations

As a large family of 2D materials, transition metal dichalcogenides(TMDs) have stimulated numerous works owing to their attractive properties. The replacement of constituent elements could promote the discovery and fabrication of new nanofilm in this family. Using precious metals, such as platinum and palladium, to serve as transition metals combined with chalcogen is a new approach to explore novel TMDs. Also, the proportion between transition metal and chalcogen atoms is found not only to exist in conventional form of 1 : 2. Herein, we reported a comprehensive study of a new 2D precious metal selenide, namely AuSe monolayer. Based on density functional theory, our result indicated that AuSe monolayer is a semiconductor with indirect band-gap of 2.0 eV, which possesses superior dynamic stability and thermodynamic stability with cohesive energy up to–7.87 eV/atom. Moreover, it has been confirmed that ionic bonding predominates in Au–Se bonds and absorption peaks in all directions distribute in the deep ultraviolet region. In addition, both vibration modes dominating marked Raman peaks are parallel to the 2D plane.     

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.     

Electronic and optical properties of ordered porous germanium

The electronic band structure and dielectric function of ordered porous Ge are studied by means of a sp³s^* tight-binding supercell model, in which periodical pores are produced by removing columns of atoms along [0 0 1] direction from a crystalline Ge structure and the pore surfaces are passivated by hydrogen atoms. The tight-binding results are compared with ab-initio calculations performed in small supercell systems. Due to the existence of periodicity in these systems, all the electron states are delocalized. However, the results of both electronic band structure and dielectric function show clear quantum confinement effects.     

Dispersive properties of Kerr-like nonlinear optical structures

The control of the group velocity dispersion (GVD) is of great concern in the design of photonic devices and may be obtained controlling the waveguide components of the GVD. Under high optical field intensity the dispersive properties of the waveguides are different from the linear state and a nonlinear model of the guide must be considered. A rib waveguide has been investigated and a finite element procedure together with a second-order perturbation technique have been used to calculate the waveguide dispersion and to compare the results in linear and nonlinear states     

Electronic device encapsulation using red phosphorus flame retardants

This paper presents an analysis of the use of red phosphorus as a flame retardant material in encapsulated microcircuits and discusses the reliability risks. Chemical reactions, which can arise when red phosphorus is exposed to ambient humidity to form highly mobile ions and oxygen-containing phosphorus acids, are presented. These ions and acids can induce electro-chemical migration, causing short circuits between leads and between wires, internal to the packaged device. Field failures caused by the red phosphorous flame retardant are also presented.     

Sb掺杂ZnO电子结构和光学性质

为了研究ZnO掺Sb后电子结构和光学性质的变化,采用基于密度泛函理论对纯净ZnO和Sb掺杂ZnO两种结构进行第一性原理的计算。计算结果表明：随着Sb的掺入,体系的晶格常数变大,键长增加,体积变大,系统总能增大。能带中价带和导带数目明显变密,费米能级进入导带,体系逐渐呈金属性,带隙明显展宽。在光学性质方面,主吸收峰的左边出现了新的吸收峰,是由导带上的Zn-4s和Sb-5p轨道杂化电子跃迁所致;同时介电函数虚部波峰发生一定程度的升高,实部静态介电常数也明显增大。     

Electronic and optical properties of the doped TiO2 system

By the total energy pseudo-potential approach of plane wave, we study the electronic and optical properties of the anatase TiO2 systems with Sc-doped, oxygen vacancies included, and Sc and oxygen vacancies co-existing, respectively. The obtained results show that the contribution by the doped Sc lies mainly in the valence band, and the light absorption in the visible region is obvious. A Mott phase transformation takes place in the presence of oxygen vacancies, and the light absorption in the visible region is also obvious. In particular, the absorption in the visible region of the co-doped system is enhanced coherently due to the influences both from doped Sc and oxygen vacancies.     

Electronic properties of InAs-based metal-insulator-semiconductor (MIS) structures

Special features of electronic processes in InAs-based MIS structures operating in the charge injection mode were investigated. These structures are used as photodetectors in the spectral range of 2.5–3.05 μm. A double-layer system consisting of an anodic oxide layer and a low-temperature silicon dioxide layer was used as an insulator. It was shown that fluorine-containing components, which were introduced into electrolyte, reduced the value of the built-in charge and the surface-state density to minimal measurable values of ≲2×10¹⁰ cm⁻² eV⁻¹. Physical and chemical characteristics of the surface states at the InAs-insulator interface and the possible causes of their absence were discussed on the basis of the phase composition data of anodic oxide obtained by X-ray photoelectron spectroscopy. An anomalous field generation was observed under the nonequilibrium depletion of the semiconductor. The processes of tunneling generation, which are important at large amplitudes of the depletion pulse, were considered. The noise behavior of MIS structures under a nonequilibrium depletion was investigated. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 9, 2001, pp. 1111–1119. Original Russian Text Copyright ? 2001 by Kuryshev, Kovchavtsev, Valisheva.     

First principles study of electronic and optical properties of the ternary SnSb4S7 using modified Becke-Johnson potential

The electronic and optical properties of SnSb₄S₇ compound are calculated by the full-potential linearized augmented plane-wave (FP-LAPW) method. The density of states (DOS) is carried out by the modified Becke-Johnson (mBJ) exchange potential approximation based on density functional theory (DFT). The compound SnSb₄S₇ has a monoclinic structure with the space group P2₁/m with lattice parameters of a=11.331 Å, b=3.865 Å and c=13.940 Å. The band gap is calculated to be 0.8 eV. The optical parameters, like dielectric constant, refractive index, reflectivity and energy loss function were also calculated and analyzed. The present work provides information about variation of the electronic and optical properties which reveals that SnSb₄S₇ is suitable for optoelectronic devices.     

Diode laser optical recording using trilayer structures

A new high-power diode laser and a more sensitive trilayer disk structure useful for FM video and digital data recording have been demonstrated. The diode laser is a constricted double-heterojunction large optical cavity (CDH-LOC) device capable of up to 100 mW output power in a single stable mode. By improving the thermal efficiency of the trilayer structure, the sensitivity is improved by a factor of two over previously reported trilayer structures. Digital signals with data rates up to 30 Mbits/s and storage capacity in excess of3 times 10^{10}bits are demonstrated using a plastic 12 in diameter disk rotating at 30 r/s while digital systems with data rates up to 60 Mbits/s and storage capacity in excess of 10¹¹bits are shown to be feasible.     

First principles study of structural,electronic and optical properties of AgSbS2

In this work, we study the structural, electronic and optical properties of AgSbS₂, using full-potential linearized augmented plane wave and the pseudopotential plane wave scheme in the frame of generalized gradient approximation. Features such as the lattice constant, bulk modulus and its pressure derivative are reported. Our results suggest a phase transition from AF-IIb phase to rocksalt (B1) phase under high pressure. The calculated band structure and density of states show that the material under load has an indirect energy band gap X→(LГ) for AF-IIb phase (semiconductor) and a negative band gap W→(ГX) for B1 phase (semimetal). The optical properties are analyzed and the origin of some peaks in the spectra is discussed. Besides, the dielectric function, refractive index and extinction coefficient for radiation up to 14 eV have also been reported and discussed.     

Operation principles of wavelength sensing using transparentproperties of semiconductor optical diodes

The wavelength-sensitive transparent properties of direct-bandgap semiconductor optical diodes (DBSODs) can be utilized for wavelength sensing. A simplified theory is used to describe the operation principles of such wavelength sensing schemes. The principles fan be applied to realize different measures, including sensing with or without pilot tone for single wavelength or multiple wavelengths. The simplified theory can also provide an easy way for estimating the wavelength resolution and accuracy. The wavelength resolution is demonstrated to be better than 0.01 nm by detecting the induced junction voltage for a fixed bias. The resolution is limited by the current resolution of the bias source to 0.03 nm when the wavelength is to be discriminated by transparent current detection. The feasibility and limitation of multiwavelength sensing using a single semiconductor optical amplifier are addressed both theoretically and experimentally. The limiting factors, including the power dependency and temperature stability, of the sensing schemes are also investigated     

Cu2ZnSnS4四种晶型的电子结构、光学性质和力学性质

本文采用密度泛函理论详细计算了Cu₂ZnSnS₄四种晶型的晶体结构、电子结构、光学性质和力学性质。结果表明它们之间在光学性质和力学性质方面没有非常明显的差异,计算结果与文献报道的实验数据基本一致。根据计算结果,Cu2ZnSnS4的基本带隙是由孤立导带的带宽来决定。Cu₂ZnSnS₄的载流子有效质量非常小,尤其是闪锌矿衍生的Cu₂ZnSnS₄在导带底具有极小的电子有效质量。根据所计算的力学常数矩阵可知,四种晶型的Cu₂ZnSnS₄; 均符合Born稳定性条件,而且较高的B/G比例表明Cu2ZnSnS4的四种晶型都具有突出可塑性。     

Characterisation of the optical properties of InGaN MQW structures using a combined SEM and CL spectral mapping system

We demonstrate the ability of a combined scanning electron microscope and cathodoluminescence(CL) spectral mapping system to provide important spatially resolved information.The degree of inhomogeneity in spectral output across a multi-quantum well sample is measured using the SEM-CL system as well as measuring the efficiency roll-off with increasing carrier concentration.The effects of low energy electron beam modification on the InGaN/GaN multi quantum wells have also been characterized.     

Characterisation of the optical properties of InGaN MQW structures using a combined SEM and CL spectral mapping system

We demonstrate the ability of a combined scanning electron microscope and cathodoluminescence (CL) spectral mapping system to provide important spatially resolved information. The degree of inhomogeneity in spectral output across a multi-quantum well sample is measured using the SEM-CL system as well as measuring the efficiency roll-off with increasing carrier concentration. The effects of low energy electron beam modification on the InGaN/GaN multi quantum wells have also been characterized.     

First principles calculations of structural,electronic and optical properties of zinc aluminum oxide

A first principles study of structural, electronic and optical properties of zinc aluminum oxide (ZnAl₂O₄) by means of the full potential linear augmented plane wave method is presented. The local density approximation is used for the exchange-correlation potential. A direct band gap of 4.19 eV, in agreement with experiment (E_g=3.9 eV), was determined. ZnAl₂O₄ is transparent in the visible spectral region; the excitonic transition associated with the fundamental band gap is 4.17 eV. The refractive index value is 1.74 in the ultraviolet spectral region.