分子束外延GaAs/GaP失配异质结材料及其性能研究

Submitted by zhangdi (zhangdi@red.semi.ac.cn) on 2009-04-13T11:45:31Z

Elasticity, band-gap bowing, and polarization of AlxGa1-xN alloys

Elastic constants, the bulk modulus, Young's modulus, band-gap bowing coefficients, spontaneous and piezoelectric polarizations, and piezoelectric coefficients of hexagonal AlxGa1-xN ternary alloys are calculated using first-principles methods. The fully relaxed structures and the structures subjected to homogeneous biaxial and uniaxial tension are investigated. We show that the biaxial tension in the plane perpendicular to the c axis and the uniaxial tension along the c axis all reduce the bulk modulus, whereas they reduce and enhance Young's modulus, respectively. We find that the biaxial and uniaxial tension can enhance the bowing coefficients. We also find that the biaxial tension can enhance the total polarization, while the uniaxial tension will suppress the total polarization. (C) 2008 American Institute of Physics.

Optical response of high-order band gap photonic crystal applying in-plane in one-dimensional integration

A new broadband filter, based on the high-order band gap in one-dimensional photonic crystal (PCs) of the form Si vertical bar air vertical bar Si vertical bar air vertical bar Si vertical bar air vertical bar Si vertical bar air vertical bar Si vertical bar air vertical bar Si, has been designed by the plane wave expansion method (PWEM) and transfer matrix method (TMM) and fabricated by lithography. The optical response of this filter to normal-incident and oblique-incident light proves that utilizing the high-order band gaps of PCs is an efficient method to lower the difficulties of fabricating PCs, increase the etching depth of semiconductor materials, and reduce the coupling loss at the interface between optical fibers and PC device. (c) 2007 Elsevier B.V. All rights reserved.

Narrowing of band gap and low-temperature spin glass behavior of FeNi co-doped ZnO nanowires

This letter reports on the Raman, optical and magnetic properties of FeNi co-doped ZnO nanowires prepared via a soft chemical solution method. The microstructural investigations show that the NiFe co-dopants are substituted into wurtzite ZnO nanostructure without forming any secondary phase. The co-doped nanowires show a remarkable reduction of 34 nm (267.9 meV) in the optical band gap, while suppression in the deep-level defect transition in visible luminescence. Furthermore, these nanowires exhibit ferromagnetism and an interesting low-temperature spin glass behavior, which may arise due to the presence of disorder and strong interactions of frustrated spin moments of Ni and Fe co-dopants on the ZnO lattice sites. Copyright (C) EPLA, 2009

Gap states and microstructure of microcrystalline silicon thin films

The density of states (DOS) above Fermi level of hydrogenated microcrystalline silicon (mu c-Si H) films is correlated to the material microstructure. We use Raman scattering and infrared absorption spectra to characterize the structure of the films made with different hydrogen dilution ratios. The DOS of the films is examined by modulated photocurrent measurement. The results have been accounted for in the framework of a three-phase model comprised of amorphous and crystalline components, with the grain boundary as the third phase. We observed that the DOS increases monotonically as the grain boundary volume fractions f(gb) is increased, which indicates a positive correlation between the DOS and the grain boundary volume fraction.

Design of Narrow-Gap TiO2: A Passivated Codoping Approach for Enhanced Photoelectrochemical Activity

To improve the photoelectrochemical activity of TiO2 for hydrogen production through water splitting, the band edges of TiO2 should be tailored to match with visible light absorption and the hydrogen or oxygen production levels. By analyzing the band structure of TiO2 and the chemical potentials of the dopants, we propose that the band edges of TiO2 can be modified by passivated codopants such as (Mo+C) to shift the valence band edge up significantly, while leaving the conduction band edge almost unchanged, thus satisfying the stringent requirements. The design principle for the band-edge modification should be applicable to other wide-band-gap semiconductors.

Band-gap bowing and p-type doping of (Zn, Mg, Be)O wide-gap semiconductor alloys: a first-principles study

Using a first-principles band-structure method and a special quasirandom structure (SQS) approach, we systematically calculate the band gap bowing parameters and p-type doping properties of (Zn, Mg, Be)O related random ternary and quaternary alloys. We show that the bowing parameters for ZnBeO and MgBeO alloys are large and dependent on composition. This is due to the size difference and chemical mismatch between Be and Zn(Mg) atoms. We also demonstrate that adding a small amount of Be into MgO reduces the band gap indicating that the bowing parameter is larger than the band-gap difference. We select an ideal N atom with lower p atomic energy level as dopant to perform p-type doping of ZnBeO and ZnMgBeO alloys. For N doped in ZnBeO alloy, we show that the acceptor transition energies become shallower as the number of the nearest neighbor Be atoms increases. This is thought to be because of the reduction of p-d repulsion. The N-O acceptor transition energies are deep in the ZnMgBeO quaternary alloy lattice-matched to GaN substrate due to the lower valence band maximum. These decrease slightly as there are more nearest neighbor Mg atoms surrounding the N dopant. The important natural valence band alignment between ZnO, MgO, BeO, ZnBeO, and ZnMgBeO quaternary alloy is also investigated.

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.

Raman scattering from GaP nanowires

A complete Raman study of GaP nanowires is presented. By comparison with the Raman spectra of GaP bulk material, microcrystals and nanoparticles, we give evidence that the Raman spectrum is affected by the one-dimensional shape of the nanowires. The Raman spectrum is sensitive to the polarization of the laser light. A specific shape of the overtones located between 600 and 800 cm(-1) is actually a signature of the nanowires. Some phonon confinement and thermal behavior is also observed for nanowires.

Two-dimensional photonic band-gap defect modes with deformed lattice

A numerical study of the defect modes in two-dimensional photonic crystals with deformed triangular lattice is presented by using the supercell method and the finite-difference time-domain method. We find the stretch or shrink of the lattice can bring the change not only on the frequencies of the defect modes but also on their magnetic field distributions. We obtain the separation of the doubly degenerate dipole modes with the change of the lattice and find that both the stretch and the shrink of the lattice can make the dipole modes separate large enough to realize the single-mode emission. These results may be advantageous to the manufacture of photonic crystal lasers and provide a new way to realize the single-mode operation in photonic crystal lasers.

Band gap narrowing in heavily B doped Si1-xGex strained layers

This paper presents a comprehensive study of the effect of heavy B doping and strain in Si1-xGex strained layers. On the one hand, bandgap narrowing (BGN) will be generated due to the heavy doping, on the other hand, the dopant boron causes shrinkage in the lattice constant of SiGe materials, thus will compensate for part of the strain. Taking the strain compensation of B into account for the first time and uesing the with semi-empirical method, the Jain-Roulston model is modified. And the real BGN distributed between the conduction and valence bands is calculated, which is important for the accurate design of SiGe HBTs.

Tunable ultra-narrow band-gap of anomalous dispersion photonic crystals

We use the transfer-matrix method to research the band structures in one-dimensional photonic crystals composed of anomalous dispersion material ( saturated atomic cesium vapor). Our calculations show that that type of photonic crystal possesses an ultra-narrow photonic band gap and this band gap is tunable when altering the electron population in the atomic ground state of the anomalous dispersion material by the optical pumping method. Copyright (C) EPLA, 2007.

Electronic structure and g factors of narrow-gap zinc-blende nanowires and nanorods

The Hamiltonian in the framework of eight-band effective-mass approximation of the zinc-blende nanowires and nanorods in the presence of external homogeneous magnetic field is given in the cylindrical coordinate. The electronic structure, optical properties, magnetic energy levels, and g factors of the nanowires and nanorods are calculated. It is found that the electron states consist of many hole-state components, due to the coupling of the conduction band and valence band. For the normal bands which are monotone functions of |k(z)|, long nanorods can be modeled by the nanowires, the energy levels of the nanorods approximately equal the values of the energy band E(k(z)) of the nanowires with the same radius at a special k(z), where k(z) is the wave vector in the wire direction. Due to the coupling of the states, some of the hole energy bands of the nanowires have their highest points at k(z)=0. Especially, the highest hole state of the InSb nanowires is not at the k(z)=0 point. It is an indirect band gap. For these abnormal bands, nanorods can not be modeled by the nanowires. The energy levels of the nanorods show an interesting plait-like pattern. The linear polarization factor is zero, when the aspect ratio L/2R is smaller than 1, and increases as the length increases. The g(z) and g(x) factors as functions of the k(z), radius R and length L are calculated for the wires and rods, respectively. For the wires, the g(z) of the electron ground state increases, and the g(z) of the hole ground state decreases first, then increases with the k(z) increasing. For the rods, the g(z) and g(x) of the electron ground state decrease as the R or the L increases. The g(x) of the hole ground state decreases, the g(z) of the hole ground state increases with the L increasing. The variation of the g(z) of the wires with the k(z) is in agreement with the variation of the g(z) of the rods with the L.