Correlation Between Lattice Strain and Energy Gap Bowing of AlxGa1-xN Epitaxial Thin Films

The correlation between the energy band-gap of AlxGa1-xN epitaxial thin films and lattice strain was investigated using both High Resolution X-ray Diffraction (HRXRD) and Spectroscopic Ellipsometry (SE). The Al fraction, lattice relaxation, and elastic lattice strain were determined for all AlxGa1-xN epilayers, and the energy gap as well. Given the type of intermediate layer, a correlation trend was found between energy band-gap bowing parameter and lattice mismatch, the higher the lattice mismatch is, the smaller the bowing parameter (b) will be.

Investigation on relationship between charge transfer position and dielectric definition of average energy gap in Eu3+-doped compounds

The dielectric definition of average energy gap E-g of the chemical bond has been calculated quantitatively in Eu3+-doped 30 lanthanide compounds based on the dielectric theory of chemical bond for complex structure crystals. The relationship between the experimental charge transfer (CT) energy of Eu3+ and the corresponding average energy gap E-g has been studied. The results show that the CT energy increases linearly with increasing of the average energy gap E-g. The linear model is obtained. It allows us to predict the CT position of Eu3+-doped lanthanide compounds with knowledge of the crystal structure and index of refraction. Applied to the Ca4GdO(BO3)(3):Eu and Li2Lu5O4(BO3)(3):Eu crystals, the predicted results of CT energies are in good agreement with the experimental values, and it can be concluded that the lowest CT energy in Li2Lu5O4(BO3)(3):Eu originates from the site of Lu1.

Effect of microstructure of TiO2 thin films on optical band gap energy

TiO2 coatings are prepared on fused silica with conventional electron beam evaporation deposition. After annealed at different temperatures for four hours, the spectra and XRD patterns of TiO2 thin film are obtained. XRD patterns reveal that only anatase phase can be observed in TiO2 coatings regardless of the different annealing temperatures, and with the increasing annealing temperature, the grain size gradually increases. The relationship between the energy gap and microstructure of anatase is determined and discussed. The quantum confinement effect is observed that with the increasing grain size of TiO2 thin film, the band gap energy shifts from 3.4 eV to 3.21 eV. Moreover, other possible influence of the TiO2 thin-film microstructure, such as surface roughness and thin film absorption, on band gap energy is also expected.

Energy spectrum of fermionized bosonic atoms in optical lattices

We investigate the energy spectrum of fermionized bosonic atoms, which behave very much like spinless noninteracting fermions, in optical lattices by means of the perturbation expansion and the retarded Green's function method. The results show that the energy spectrum splits into two energy bands with single-occupation; the fermionized bosonic atom occupies nonvanishing energy state and left hole has a vanishing energy at any given momentum, and the system is in Mott-insulating state with a energy gap. Using the characteristic of energy spectra we obtained a criterion with which one can judge whether the Tonks-Girardeau (TG) gas is achieved or not.

Energy spectrum of ground state and excitation spectrum of quasi-particle for hard-core boson in optical lattices

We investigate the energy spectrum of ground state and quasi-particle excitation spectrum of hard-core bosons, which behave very much like spinless noninteracting fermions, in optical lattices by means of the perturbation expansion and Bogoliubov approach. The results show that the energy spectrum has a single band structure, and the energy is lower near zero momentum; the excitation spectrum gives corresponding energy gap, and the system is in Mott-insulating state at Tonks limit. The analytic result of energy spectrum is in good agreement with that calculated in terms of Green's function at strong correlation limit.

Strain relaxation and band-gap tunability in ternary InxGa1-xN nanowires

The alloy formation enthalpy and band structure of InGaN nanowires were studied by a combined approach of the valence-force field model, Monte Carlo simulation, and density-functional theory (DFT). For both random and ground-state structures of the coherent InGaN alloy, the nanowire configuration was found to be more favorable for the strain relaxation than the bulk alloy. We proposed an analytical formula for computing the band gap of any InGaN nanowires based on the results from the screened exchange hybrid DFT calculations, which in turn reveals a better band-gap tunability in ternary InGaN nanowires than the bulk alloy.

Quantifying robustness and dissipation cost of yeast cell cycle network: The funneled energy landscape perspectives

We study the origin of robustness of yeast cell cycle cellular network through uncovering its underlying energy landscape. This is realized from the information of the steady-state probabilities by solving a discrete set of kinetic master equations for the network. We discovered that the potential landscape of yeast cell cycle network is funneled toward the global minimum, G1 state. The ratio of the energy gap between G1 and average versus roughness of the landscape termed as robustness ratio ( RR) becomes a quantitative measure of the robustness and stability for the network. The funneled landscape is quite robust against random perturbations from the inherent wiring or connections of the network. There exists a global phase transition between the more sensitive response or less self-degradation phase leading to underlying funneled global landscape with large RR, and insensitive response or more self-degradation phase leading to shallower underlying landscape of the network with small RR. Furthermore, we show that the more robust landscape also leads to less dissipation cost of the network. Least dissipation and robust landscape might be a realization of Darwinian principle of natural selection at cellular network level. It may provide an optimal criterion for network wiring connections and design.

Energy landscape theory, funnels, specificity, and optimal criterion of biomolecular binding

We study the nature of biomolecular binding. We found that in general there exists several thermodynamic phases: a native binding phase, a non-native phase, and a glass or local trapping phase. The quantitative optimal criterion for the binding specificity is found to be the maximization of the ratio of the binding transition temperature versus the trapping transition temperature, or equivalently the ratio of the energy gap of binding between the native state and the average non-native states versus the dispersion or variance of the non-native states. This leads to a funneled binding energy landscape.

Quantum Efficiency And Temperature Coefficients Of Gainp/Gaas Dual-Junction Solar Cell

GaInP/GaAs dual-junction solar cell with a conversion efficiency of 25.2% has been fabricated using metalorganic chemical vapor deposition (MOCVD) technique. Quantum efficiencies of the solar cell were measured within a temperature range from 25 to 160A degrees C. The results indicate that the quantum efficiencies of the subcells increase slightly with the increasing temperature. And red-shift phenomena of absorption limit for all subcells are observed by increasing the cell's work temperature, which are consistent with the viewpoint of energy gap narrowing effect. The short-circuit current density temperature coefficients dJ (sc)/dT of GaInP subcell and GaAs subcell are determined to be 8.9 and 7.4 mu A/cm(2)/A degrees C from the quantum efficiency data, respectively. And the open-circuit cell voltage temperature coefficients dV (oc)/dT calculated based on a theoretical equation are -2.4 mV/A degrees C and -2.1 mV/A degrees C for GaInP subcell and GaAs subcell.

Spectroscopic and fluorescence decay behaviors of Yb3+ -doped SiO2-PbO-Na2O-K2O glass

The spectroscopic and fluorescent decay behaviors of Yb3+-doped SiO2-PbO-Na2O-K2O glass is reported in this work. Yb2O3 contents of 1, 1.5 and 2mol% are added into the glass. Through the measurement of absorption and fluorescence spectra, and fluorescent decay rate at room temperature and at low temperature (18 K), it is found that the nonradiative decay rate of Yb3+ ions is mainly determined by the interaction between residual hydroxyl groups and Yb3+ ions. Concentration quenching effect can be omitted in this glass up to the Yb3+ ion concentration of 8.98 x 10(20)/cm(3). Multiphonon decay rate is also very small because of the large energy gap between F-2(5/2) and F-2(7/2) levels of Yb3+ ions. (c) 2004 Elsevier B.V. All rights reserved.

射频磁控溅射法制备TiO2-xNX薄膜的结构性能研究

利用射频磁控溅射法室温下在Si（100）衬底上制备了N掺杂的TiO2薄膜，并且采用x射线衍射（XRD）、X射线光电子能谱（XPS）和透射光谱对薄膜进行了表征。XRD结果表明在纯Ar和N2（33．3％）／Ar气氛下制备的TiO2-xNx薄膜均为单一的金红石相，薄膜结晶性良好，呈高度（211）择优取向，而在N2（50．0％）／Ar下制备的薄膜结晶性明显变差；对于N掺杂的TiO2薄膜，XPS表明部分N原子进入TiO2晶格，并且以N—Ti—O、N—O键以及间隙式N原子形式存在；透射光谱表明掺N后的TiO2薄膜吸收边发生了红移。

Structural and optical properties of Al1-xInxN epilayers on GaN template grown by metalorganic chemical vapor deposition

This paper reports that Al1-xInxN epilayers were grown on GaN template by metalorganic chemical vapor deposition with an In content of 7%-20%. X-ray diffraction results indicate that all these Al1-xInxN epilayers have a relatively low density of threading dislocations. Rutherford backscattering/channeling measurements provide the exact compositional information and show that a gradual variation in composition of the Al1-xInxN epilayer happens along the growth direction. The experimental results of optical reflection clearly show the bandgap energies of Al1-xInxN epilayers. A bowing parameter of 6.5 eV is obtained from the compositional dependence of the energy gap. The cathodoluminescence peak energy of the Al1-xInxN epilayer is much lower than its bandgap, indicating a relatively large Stokes shift in the Al1-xInxN sample.

Electronic structure and optical properties of GaN with Mn-doping

Calculations of the electronic structure and the density of states of GaN with Mn are carried out by means of first-principles plane-wave pesudopotential method based on density functional theory. The results reveal a 100% spin polarized impurity band in band structure of Ga1-xMnxN due to hybridization of Mn 3d and N 2p orbitals. The material is half metallic and suited for spin injectors. In addition, a peak of refractive index can be observed near the energy gap. The absorption coefficient increases in the UV region with the increase of the Mn content.

Oxygen pressure dependences of structure and properties of ZnO films deposited on amorphous glass substrates by pulsed laser deposition

ZnO films are prepared on glass substrates by pulsed laser deposition (PLD) at different oxygen pressures, and the effects of oxygen pressure on the structure and optoelectrical properties of as-grown ZnO films are investigated. The results show that the crystallite size and surface roughness of the films increase, but the carrier concentration and optical energy gap E-g decrease with increasing oxygen pressure. Only UV emission is found in the photoluminescence (PL) spectra of all the samples, and its intensity increases with oxygen pressure. Furthermore, there are marked differences in structure and properties between the films grown at low oxygen pressures (0.003 and 0.2 Pa) and the films grown at high oxygen pressures (24 and 150 Pa), which is confirmed by the fact that the crystallite size and UV emission intensity markedly increase, but the carrier concentration markedly decreases as oxygen pressure increases from 0.2 to 24 Pa. These results show that the crystal quality, including the microstructural quality and stoichiometry proportion, of the prepared ZnO films improves as oxygen pressure increases, particularly from 0.2 to 24 Pa.