Structural, Optical and Electrical Properties of ZnS/Porous Silicon Heterostructures

ZnS films are deposited by pulsed laser deposition on porous silicon （PS） substrates formed by electrochemical anodization of p-type （100） silicon wafer. Scanning electron microscope images reveal that the surface of ZnS films is unsmoothed, and there are some cracks in the ZnS films due to the roughness of the PS surface. The x-ray diffraction patterns show that the ZnS films on PS surface are grown in preferring orientation along cubic phase β-ZnS （111） direction. White light emission is obtained by combining the blue-green emission from ZnS films with the orange-red emission from PS layers. Based on the I-V characteristic, the ZnS/PS heterojunction exhibits the rectifying junction behaviour, and an ideality factor n is calculated to be 77 from the I-V plot.     

Structural and Optical Characteristics of InGaN／GaN Multi-Quantum Wells Grown on α-and c-Plane Sapphire Substrates

We investigate the structural and optical properties of InGaN-based multi-quantum wells grown on α-c plane sapphire substrates by atomic force microscopy, high-resolution x-ray diffraction and temperature-dependent photoluminescence measurements. The multi-quantum wells grown on α-plane sapphire substrate show stronger exciton localization effect compared with that grown on the c-plane substrate, although the threading dislocation densities in the two samples are almost the same. We attribute the results to the different in-plane strain of quantum well grown on different substrate orientations at the same growth temperature. Since the excitonloca lization effect plays a key role to obtain high efficiency InGaN-based optoelectronics devices, the presented result should be emphasized.     

Structural, Morphology and Optical Properties of Epitaxial ZnO Films Grown on Al2O3 by MOCVD

Epitaxial ZnO films are grown on Al2O3 （0001） by the MOCVD method. These films are high quality wurtzite crystals with （0001） orientation. Big hexagonal crystallites （diameter from several decades to 100 μm） are found on the surface. Inside these crystallites, a stronger luminescence is observed compared with the plain area. Transmission electronic microscopy reveals that the film is thicker inside the hexagonal crystallites than the plain area, and some crystallites are not connected with each other and are slightly rotated with respect to their neighbours.     

Comparisons of Structural and Optical Properties of ZnO films Grown on Sapphire and Si（001）

Zinc oxide films were grown on sapphire and Si(001) substrates by reactive electron beam evaporation at low substrate temperatures,Atomic force microscopy(AFM),x-ray diffraction(XRD),and photoluminescence excitation(PLE) are employed to characterize the as-grown films.The AFM measurements have shown that all of the ZnO films present pillar-like growth properties.but the dimensional uniformity of the ZnO crystal pillars grown on sapphire was better than that on Si(001),The XRD results indicated that the prepared ZnO films both on sapphire and Si(001) were all highly c-axis oriented.the linewidths of ZnO(002)are only 0.19 and 0.28,respectively,The PLE characterizations revealed the continum absorption of the samples grown on sapphire,However,in the PLE spectra of the ZnO films grown on Si(001) substrates,a broad peak appears at the high-energy region,which indicates the formation of ZnO quantum dot structures on Si(001).     

Effects of Single Vacancy on Electronic and Optical Properties for γ-Si3N4

基于密度泛函理论的广义梯度近似方法研究了中性单点缺陷γ-Si₃N₄的能量、电子结构和光学性质. N缺陷的结合能和形成能比Si(8)和Si(4)位的都低,显示γ-Si₃N₄中N缺陷更易形成. 分析了各种缺陷情况下相应的态密度. Si缺陷能形成p型半导体,N缺陷使材料形成间接带隙的n型半导体. Si缺陷情况下,物质有相对大的静态介电常数,在可见光区和红外区,吸收和反射得到显著改善,但是N缺陷却没什么影响.     

Growth and Optical Properties of Double Heterostructure GaN／InGaN／GaN Films with Large Composition

The double heterostructure GaN/InGaN/GaN films with different thicknesses of the InGaN layer were grown at 780℃ or 800℃ by metal-organic chemical vapour deposition.The samples were investigated using x-ray diffraction (XRD),room-temperature photoluminescence (PL) and Raman scattering.The dependences of the samples on both the growth temperature and the thickness of the InGaN layer were studied.The composition of InGaN was determined by the results of XRD,and the bowing parameter of InGaN was calculated in terms of the PL spectra.When the thickness of the InGaN layer was reduced,the phase separation of InGaN was found in some samples.The raman frequency of the A1(LO) and E2(low) modes in all the samples shifted and did not agree with Vegard‘s law.     

Synthesis and Optical Properties of ZnO Nanostructures

ZnO nanostructures with different morphologies were fabricated by changing the partial oxygen pressure. The structures, morphologies and optical properties of ZnO nanostructures were investigated by x-ray diffraction, field emission scanning electron microscopy and photoluminescence (PL) spectra at room temperature. All the samples show preferred orientation along the c-axis. The oxygen partial pressure and the annealing atmosphere have important effect on the PL property of ZnO nanostructures. The high oxygen partial pressure during growth of samples and high-temperature annealing of the ZnO samples in oxygen can increase oxygen vacancies and can especially increase antisite oxygen (OZn) defects, which degraded the near band-edge emission. However, the annealing in 1-12 can significantly modify the NBE emission.     

Optical Characterization of β-FeSi2 Thin Films Prepared by Femtosecond Laser Ablation

Iron disilicide thin films are prepared on fused quartz using femtosecond laser deposition （FsPLD） with a FeSi2 alloy target. X-ray diffraction results indicate the films are single-phase, orthorhombic, β-FeSi2. Field scanning electron microscopy, high resolution transmission electron microscopy, UV-VIS-NIR spectroscopy and Raman microscope are used to characterize the structure, composition, and optical properties of the β-FeSi2 films. Normal incidence spectral transmittance and reflectance data indicate a minimum, direct energy gap of 0.85 eV. The two most intense lines of Raman scattering peaked at 181.3 cm^-1 and 235.6cm^-1 for the film on fused quartz, and at 191.2cm^-1 and 243.8cm^-1 for the film on Si （100）, are observed.     

Structural and Optical Properties of Zinc Nitride Films Prepared by Pulsed Filtered Cathodic Vacuum Arc Deposition

Polycrystalline zinc nitride films are deposited on Coming 7059 glass substrates by pulsed filtered cathodic vacuum arc deposition （PFCVAD）. The crystallographic structure is studied by means of x-ray diffraction. These measurements show that all the films are crystallized in the cubic structure, in a preferred orientation along the （332） and （631） directions. Weak XRD signal shows small crystallites distributed in an amorphous tissue. A small improvement of crystallinity is observed with annealing. Optical parameters such as absorption, energy band gap, Urbach tail, extinction coefficients have been determined. The Urbach tail energy is decreased with annealing at 500℃ for one hour. Energy band gap values are found to be increased by annealing.     

Preparation and Optical Properties of SnO2／SiO2 Nanocomposite

SnO2/SiO2 nanocomposites have been prepared by the soaking-thermal-decomposing method, tin oxide nanoparticles are uniformly dispersed in the mesopores of silica. The optical absorption edge of the obtained nanocomposite presents a redshift compared with bulk tin oxide, With the increasing annealing temperature during the procedure of the sample preparation, the optical absorption edge of the sample moves to shorter wavelength (blueshift). These optical properties can be ascribed to the amorphous structure and band defects of surface layers of the tin oxide nanoparticles.     

Structural and Photoluminescence Properties of β-Ga2O3 Nanofibres Fabricated by Electrospinning Method

We have prepared the 13-Ga2 O3 nanofibres by electrospinning method followed by calcining in air at 900℃. The morphology and structure of the nanofibres are characterized by field emission scanning electron microscopy （FE-SEM）, x-ray diffraction （XRD） and Raman technique. These nanofibres have diameters ranging from 60 to 130hm and lengths up to several millimetres. Photoluminescence （PL） spectrum under excitation at 325 nm shows that theseβ-Ga2 O3 nanofibres have a blue emission peaking at 466nm, which may be attributed to defects such as the oxygen vacancies, gallium vacancies and gallium-oxygen vacancy pairs.     

Optical Properties and Structure Analyses of Zinc Sulfide Nanorods

ZnS nanorods were synthesized using solvothermal process with ethylenediamine as a bidentate ligand to form Zn^2 complexes and dodecylthiol providing an effective control over the crystal growth of ZnS nanorod. The microstructure of the nanorods was characterized by x-ray diffraction and transmission-electron microscopy. The optical properties of ZnS nanorods were examined by the photoluminescence spectrum.     

Electronic Structural Properties and Superconductivity of Diborides in the MgB2 Structure

We calculate the critical temperature Tc of a wide range of diborides which have the same crystal structure as MgB2.Their electronic structure is also calculated in the framework of the local density approximation method of density functional theory be using the pseudopotential plane wave approach.The Hopfield factors η of these materials are calculated by the frozen phonon method.Our results show that most of these diborides have low η,and hence low or no Tc;this is consistent with experimental observations.The most important result of our calculation is that AgB2 and AuB2 have higher Tc than MgB2.The high Tc of these two materials comes from the combination of the high density of states and high deformation potential of the σ bands.     

Effect of annealing on photoluminescence and microstructures of InGaN／GaN multi-quantum well with Mg-doped p-type GaN

InGaN/GaN multi-quantum well structure with Mg-doped p-type GaN was grown by low-pressure metalorganic vapour phase epitaxy. After rapid-thermal-annealing at 700 and 900${^\circ}$C, both the red-shift and the blue-shift of the photoluminescence (PL) peak, the decreased and the enhancement of the PL intensity were observed. The transmission electron microscopic images showed that InGaN multi-quantum-dots-like (MQD-like) structures with dimensions less than 5$\tm$10nm were formed in InGaN wells. The changes of PL spectra could be tentatively attributed to the competition between the red-shift mechanism of the quantum-confined Stark effect and the blue-shift mechanism of the quantum size effect due to MQD-like structures.     

Ellipsometric Spectra and Optical Properties of Anisotropic SrBi2Ta2O9 Films

Ellipsometric spectra of the SrBi2 Ta2O9 (SBT) films of (200) and (0010) predominant orientation are measured and analysed in the range of photon energy from 2 to 5 eV.The results show that the oriented SBT films appear to be strongly anisotropic.The ellipsometric spectra of the (200)-predominant SBT films are different from those of the (O010)-predominant films.We suggest an analysis model for these oriented films and perform the fitting of the anisotropic ellipsometric spectra.The refractive index and the extinction coefficient of the ordinary ray and the extraordinary ray for these oriented SBT films are obtained.The ordinary refractive index is larger than the extraordinary one.     

Structural Peculiarities and Magnetic Properties of Nanoscale Terbium in Tb/Ti and Tb/Si Multilayers

The structure and the magnetic properties of rf-sputtered nauoscale Tb in [Tb/Ti]n and [Tb/Si] multilayers have been studied experimentally. It is found that the structure of Tb layers changes, transforming from a fine-crystalline state of Tb into an amorphous state as the magnetic layer thickness decreases. The observed displacement of a magnetic ordering temperature to the lower temperature range and the shift of magnetic hysteresis obtained in the ZFC-FC terms may be caused by the size effect and the amorphization. Both the first and the second suppress the exchange interaction and decrease the crystalline magnetic anisotropy. The type of material of nonmagnetic spacers between the Tb layers plays a certain role in these changes.     

Influence of LiB3O5 Structure on Microstructure and Optical Properties of ZrO2 Thin Films Prepared by Electron Beam Evaporation

ZrO2 thin films were deposited by using an electron beam evaporation technique on three kinds of lithium triborate (LIB3O5 or LBO) substrates with the surfaces at specified crystalline orientations. The influences of the LBO structure on the structural and optical properties of ZrO2 thin films are studied by spectrophotometer and x-ray diffraction. The results indicate that the substrate structure has obvious effects on the structural and optical properties of the film: namely, the ZrO2 thin film deposited on the X-LBO, Y-LBO and Z-LBO orients to m(-212), rn(021) and o(130) directions. It is also found that the ZrO2 thin film with m(021) has the highest refractive index and the least lattice misfit.     

Structural and Magnetic Properties of Codoped ZnO based Diluted Magnetic Semiconductors

Zn1-xCoxO （x = 0.01, 0.02, 0.05, 0.10 and 0.20） diluted magnetic semiconductors are prepared by the sol-gel method. The structural and magnetic properties of the samples are studied using x-ray diffraction （XRD）, extended x-ray absorption fine structure （EXAFS） and superconducting quantum interference device （SQUID）. The XRD patterns does not show any signal of precipitates that are different from wurtzite type ZnO when Co content is lower than x = 0.10. An EXAFS technique for the Co K-edge has been employed to probe the local structures around Co atoms doped in ZnO powders by fluorescence mode. The simulation results for the first shell EXAFS signals indicate that Zn sites can be substituted by Co atoms when Co content is lower than x = 0.05. The SQUID results show that the samples （x 〈 0.05） exhibit clear hysteresis loops at 300K, and magnetization versus temperature from 5 K to 350K at H = 100 Oe for the sample x = 0.02 shows that the samples have ferromagnetism above room temperature. A double-exchange mechanism is proposed to explain the ferromagnetic properties of the samples.     

Rapid Thermal Annealing Effects on Structural and Optical Properties of Self-Assembled InAs／GaAs Quantum Dots Capped by InAIAs／InGaAs Layers

Effects of rapid thermal annealing on the optical and structural properties of self-assembled InAs/GaAs quantum dots capped by the InAlAs/InGaAs combination layers are studied by photoluminescence and transmission electron microscopy. The photoluminescence measurement shows that the photoluminescence peak of the sample after 850℃ rapid thermal annealing is blue shifted with 370meV and the excitation peak intensity increases by a factor of about 2.7 after the rapid thermal annealing, which indicates that the InAs quantum dots have experienced an abnormal transformation during the annealing. The transmission electron microscopy shows that the quantum dots disappear and a new InAlGaAs single quantum well structure forms after the rapid thermal annealing treatment. The transformation mechanism is discussed. These abnormal optical properties are attributed to the structural transformation of these quantum dots into a single quantum well.     

Theoretical study on structures of Ga3N, GaN3, Ga3N2 and Ga2N3 clusters

The structures of Ga_3N, GaN_3, Ga_3N_2 and Ga_2N_3 clusters are studied using the full-potential linear-muffin-tin-orbital molecular dynamics (FP-LMTO MD) method. Four structures for Ga_3 N, five structures for GaN_3, nine structures for Ga_3N_2 and nine structures for Ga_2N_3 have been obtained. The most stable structures of these clusters are planar ones. A strong dominance of the N－-N bond over the Ga－-N and Ga－-Ga bonds appears to control the structural skeletons, supporting the previous result obtained by Kandalam and co-workers. The most stable structures of these small GaN clusters displayed semiconductor-like properties through the calculation of the HOMO－LUMO gaps.