The wave function evolution of an exciton in a bilayer system: Turning on a static in-plane electric field

The time evolution of the ground state wave function of an exciton in an ideal bilayer system is investigated within the framework of the effective-mass approximation. All of the moduli squared of the ground state wave functions evolve with time as cosine functions after an in-plane electric field is applied to the bilayer system. The variation amplitude and period of the modulus squared of the ground state wave function increase with the in-plane electric field F-r for a fixed in-plane relative coordinate r and fixed separation d between the electron and hole layers. Moreover, the variation amplitude and period of the modulus squared of the ground state wave function increase with the separation d for a fixed r and fixed in-plane electric field. Additionally, the modulus squared of the ground state wave function decreases as r increases at a given time t for fixed values of d and F-r. (c) 2007 American Institute of Physics.

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.

Effects of the wave function localization in AlInGaN quaternary alloys

Using the first-principles band-structure method and the special quasirandom structures approach, the authors have investigated the band structure of random AlxInyGa1-x-yN quaternary alloys. They show that the wave functions of the band edge states are more localized on the InN sites. Consequently, the photoluminescence transition intensity in the alloy is higher than that in GaN. The valence band maximum state of the quaternary alloy is also higher than GaN with the same band gap, indicating that the alloy can be doped more easily as p-type. (c) 2007 American Institute of Physics.

Optimization of tried wave-function in quantum monte-carlo method

A method for optimizing tried wave functions in quantum Monte Carlo method has been found and used to calculate the energies of molecules, such as H-2, Li-2, H-3+, H-3 and H-4. Good results were obtained.

Ground-state energy shifts of H-like Ti under dense and hot plasma conditions

In this study, by adopting the ion sphere model, the self-consistent. field method is used with the Poisson-Boltzmann equation and the Dirac equation to calculate the ground-state energies of H-like Ti at a plasma electron density from 10(22) cm(-3) to 10(24) cm(-3) and the electron temperature from 100 eV to 3600 eV. The ground-state energy shifts of H-like Ti show different trends with the electron density and the electron temperature. It is shown that the energy shifts increase with the increase in the electron density and decrease with the increase in the electron temperature. The energy shifts are sensitive to the electron density, but only sensitive to the low electron temperature. In addition, an accurately fitting formula is obtained to fast estimate the ground-state energies of H-like Ti. Such fitted formula can also be used to estimate the critical electron density of pressure ionization for the ground state of H-like Ti.

Mechanical and chemical bonding properties of ground state BeH2

The crystal structure, mechanical properties and electronic structure of ground state BeH2 are calculated employing the first-principles methods based on the density functional theory. Our calculated structural parameters at equilibrium volume are well consistent with experimental results. Elastic constants, which well obey the mechanical stability criteria, are firstly theoretically acquired. The bulk modulus B, Shear modulus G, Young's modulus E, and Poisson's ratio upsilon are deduced from the elastic constants. The bonding nature in BeH2 is fully interpreted by combining characteristics in band structure, density of states, and charge distribution. The ionicity in the Be-H bond is mainly featured by charge transfer from Be 2s to H 1s atomic orbitals while its covalency is dominated by the hybridization of H 1s and Be 2p states. The Bader analysis of BeH2 and MgH2 are performed to describe the ionic/covalent character quantitatively and we find that about 1.61 (1.6) electrons transfer from each Be (Mg) atom to H atoms.

First-principles study of ground-state properties and high pressure behavior of ThO2

The mechanical properties, electronic structure and phonon dispersion of ground state ThO2 as well as the structure behavior up to 240 GPa are studied using first-principles density-functional theory. Our calculated elastic constants indicate that both the ground-state fluorite structure and high pressure cotunnite structure of ThO2 are mechanically stable. The bulk modulus, shear modulus, and Young's modulus of cotunnite ThO2 are all smaller by approximately 25% compared with those of fluorite ThO2. The Poisson's ratios of both structures are approximately equal to 0.3 and the hardness of fluorite ThO2 is 22.4 GPa. The electronic structure and bonding nature of fluorite ThO2 are fully analyzed, and show that the Th-O bond displays a mixed ionic/covalent character. The phase transition from the fluorite to cotunnite structure is calculated to occur at the pressure of 26.5 GPa, consistent with recent experimental measurement by ldiri et al. [1]. For the cotunnite phase it is further predicted that an isostructural transition takes place in the pressure region of 80-130 GPa.

Electron ground state energy level determination of ZnSe self-organized quantum dots embedded in ZnS

Optical and electrical characterization of the ZnS self-organized quantum dots (QDs) embedded in ZnS by molecular beam epitaxy have been investigated using photoluminescence (PL), capacitance-voltage (C-V), and deep level transient Fourier spectroscopy (DLTFS) techniques. The temperature dependence of the free exciton emission was employed to clarify the mechanism of the PL thermal quenching processes in the ZnSe QDs. The PL experimental data are well explained by a two-step quenching process. The C-V and DLTFS techniques were used to obtain the quantitative information on the electron thermal emission from the ZnSe QDs. The correlation between the measured electron emission from the ZnSe QDs in the DLTFS and the observed electron accumulation in the C-V measurements was clearly demonstrated. The emission energy for the ground state of the ZnSe QDs was determined to be at about 120 meV below the conduction band edge of the ZnS barrier, which is in good agreement with the thermal activation energy, 130 meV, obtained by fitting the thermal quenching process of the free exciton PL peak. (C) 2003 American Institute of Physics.

A method to obtain ground state electroluminescence from 1.3 mu m emitting InAs/GaAs quantum dots grown by molecular beam epitaxy

1.3 mum emitting InAs/GaAs quantum dots (QDs) have been grown by molecular beam epitaxy and QD light emitting diodes (LEDs) have been fabricated. In the electroluminescence spectra of QD LEDs, two clear peaks corresponding to the ground state emission and the excited state emission are observed. It was found that the ground state emission could be achieved by increasing the number of QDs contained in the active region because of the state filling effect. This work demonstrates a way to control and tune the emitting wavelength of QD LEDs and lasers.

Room-temperature, ground-state lasing for red-emitting vertically aligned InAlAs/AlGaAs quantum dots grown on a GaAs(100) substrate

The effect of the growth temperature on the properties of InAlAs/AlGaAs quantum dots grown on GaAs(100) substrates is investigated. The optical efficiency and structural uniformity are improved by increasing the growth temperature from 530 to 560 degreesC. The improvements of InAlAs/AlGaAs quantum-dot characteristics could be explained by suppressing the incorporation of oxygen and the formation of group-III vacancies. Furthermore, edge-emitting laser diodes with six quantum-dot layers grown at 560 degreesC have been fabricated. Lasing occurs via the ground state at 725 nm, with a room-temperature threshold current density of 3.9 kA/cm(2), significantly better than previously reported values for this quantum-dot systems. (C) 2002 American Institute of Physics.

Double-wave function of RLC circuit after quantization

Quantization of RLC circuit is given and described by a double-wave function. A comparison between classical limit result and those of classical theory is made.

Ground-state properties of an artificial molecule: a simple model calculation for the double quantum dot

The ground state of a double quantum-dot structure is studied by a simplified Anderson-type model. Numerical calculations reveal that the ground-state level of this artificial molecule increases with the increasing single particle level of the dot, and also increases with the decreasing transfer integrals. We show the staircase feature of the electron occupation and the properties of the ground-state eigenvector by varying the;single particle level of the dot.

On detection wavelength and electron-hole wave function overlap of type II InAs/In-x Ga1-x Sb superlattice infrared photodetector

In this paper, the detection wavelength and the electron-hole wave function overlap of InAs/IrxGa1-xSb type II superlattice photodetectors are numerically calculated by using the envelope function and the transfer matrix methods. The band offset is dealt with by employing the model solid theory, which already takes into account the lattice mismatch between InAs and InxGa1-xSb layers. Firstly, the detection wavelength and the wave function overlap are investigated in dependence on the InAs and InxGa1-xSb layer thicknesses, the In mole fraction, and the periodic number. The results indicate that the detection wavelength increases with increasing In mole fraction, InAs and InxGa1-xSb layer thicknesses, respectively. When increasing the periodic number, the detection wavelength first increases distinctly for small periodic numbers then increases very slightly for large period numbers. Secondly, the wave function overlap diminishes with increasing InAs and InxGa1-xSb layer thicknesses, while it enhances with increasing In mole fraction. The dependence of the wave function overlap on the periodic number shows the same trend as that of the detection wavelength on the periodic number. Moreover, for a constant detection wavelength, the wave function overlap becomes greater when the thickness ratio of the InAs over InxGa1-xSb is larger.

A broadband external cavity tunable InAs/GaAs quantum dot laser by utilizing only the ground state emission

A broadband external cavity tunable laser is realized by using a broad-emitting spectral InAs/GaAs quantum dot (QD) gain device. A tuning range of 69 nm with a central wavelength of 1056 nm, is achieved at a bias of 1.25 kA/cm(2) only by utilizing the light emission from the ground state of QDs. This large tunable range only covers the QD ground-state emission and is related to the inhomogeneous size distribution of QDs. No excited state contributes to the tuning bandwidth. The application of the QD gain device to the external cavity tunable laser shows its immense potential in broadening the tuning bandwidth. By the external cavity feedback, the threshold current density can be reduced remarkably compared with the free-running QD gain device.