The self-consistent cell model equation of state for solids

An anharmonic equation of state for solids using the Self-Consistent Cell Model (SCCM) is given in a form useful for calculating the usual thermodynamic properties. Following Cowley and Shukla, using the Jaswal-Girifalco potential for copper, calculations are compared with other models and with experiment. The results from the analytic expressions using the SCCM are as good or better than those obtained from far more complicated theories of anharmonicity. Using the Lindemann criterion, the pressure at the melting point was obtained as a function of the melting temperature. A melting line was also obtained for iron and the longitudinal velocity and isothermal bulk modulus along the melting line were calculated. The Hugoniot pressures were calculated and compared with experiment. For both the copper and iron the agreement between theory and experiment is remarkably good considering the empirical nature of the potentials, the simplifying approximations of the SCCM calculations, and the large range of densities and pressures that are compared with experiment.     

Quantum reflection pole method for determination of quasibound states in semiconductor heterostructures

The quantum reflection pole method (QRPM) is introduced for determining quasibound state eigenenergies and their lifetimes in symmetric, asymmetric, biased, and unbiased quantum heterostructures. In the QRPM the single-band effective-mass Schrödinger equation is solved without using complex arithmetic. Calculations are much simpler to perform than with previous methods. Further, results are found to be in excellent agreement with other rigorous techniques.     

Ξ^-t quasibound state instead of ΛΛnn bound state

The coupledΛΛnn-Ξ-pnn system was studied to investigate whether the inclusion of channel coupling is able to bind theΛΛnn system.We use a separable potential three-body model of the coupledΛΛnn-Ξ-pnn system and a variational four-body calculation with realistic interactions.Our results exclude the possibility of aΛΛnn bound state by a large margin.Instead,we found aΞ-t quasibound state above theΛΛnn threshold.     

Faddeev calculation of a K- pp quasibound state

We report on the first genuinely three-body K[over]NN- piSigmaN coupled-channel Faddeev calculation in search for quasibound states in the K- pp system. The main absorptivity in the K- p subsystem is accounted for by fitting to K- p data near threshold. Our calculation yields one such quasibound state, with I=1/2, J{pi}=0-, bound in the range B approximately 55-70 MeV, with a width of Gamma approximately 90-110 MeV. These results differ substantially from previous estimates, and are at odds with the K- pp-->Lambda p signal observed by the FINUDA collaboration.     

Dipole matrix elements of semiconductor intersubband quantum structures

A method for determining the dipole matrix element for an intersubband optical transition in multi-layered semiconductor quantum heterostructures is presented. The single-band effective-mass Schrödinger equation is solved by employing the argument principle method (APM) to extract the bound (B) and quasibound (QB) eigenenergies of the quantum heterostructure. The major types of optical transitions involving bound and QB states are defined and the corresponding dipole matrix elements are calculated for each type. The method presented incorporates the energy-dependent effective mass of electrons arising from conduction-band nonparabolicity. The performance and the accuracy of the method are evaluated for an asymmetric Fabry–Perot electron wave interference filter. The physical dimensions of the filter are varied to show their effect on the dipole matrix elements. Results with and without nonparabolic effects are presented and compared. Dipole matrix elements are also calculated for the filter with an applied electric field bias. In this case the eigenstate wavefunctions can be expanded as linear combinations of Airy and complementary Airy functions. In addition, results from the present method are compared to a Kronig–Penney and a multi-band model. The dipole matrix element values calculated by the present method are shown to be in excellent agreement with the values obtained from these models. Further, the present model is numerically efficient and easily implemented.     

The self-consistent average phonon equation of state for ionic crystals

The self-consistent average phonon (SCAP) approximation was successful in describing the thermodynamic properties of monatomic solids. This formalism was extended to ionic crystals (specifically sodium chloride) at two levels of approximation: (1) the phonon frequencies replaced by a single average frequency, and (2) the phonon frequencies replaced by two average frequencies corresponding to the usual acoustic and optic phonons. In order to compare with earlier calculations and with experiments various forms of the interatomic potential (with polarization neglected) were used. The SCAP calculation is in good agreement with experiment at low and medium temperatures but underestimates the high temperature thermal expansion. It is concluded that the SCAP formalism with polarization included should give a good approximation to the thermodynamic properties of simple ionic crystals over the entire temperature range.     

Photoexcitation of a quasibound delta-nucleus state of a nucleus

The photoproduction of negatively charged pions on a carbon nucleus in the (γ, π ^?, p) and (γ, π ^?, pp) reactions is studied experimentally. The results of the respective measurements are explained on the basis of a model that assumes the formation of an intermediate quasibound delta-nucleus state (delta nucleus) that decays via the emission of a pion and a nucleon. The delta-nucleus mass and width are estimated for the example of ¹¹B_Δ.     

Convergence of the Godunov scheme for a simplified one-dimensional hydrodynamic model for semiconductor devices

Convergence of approximate solutions derived by the Godunov scheme for a simplified one-dimensional hydrodynamic model for semiconductor devices is established by using the compensated compactness method. A global existence theorem is shown; and a numerical method for the computation of the physical global solution of this model is provided by this approach.     

The potential of n-i-p-i doping superlattices for novel semiconductor devices

In this paper we suggest a number of device applications of n-i-p-i doping superlattices. The concept of these devices is based on the unusual electronic properties of this new class of semiconductors such as extremely long excess carrier lifetime, tunable band gap and carrier concentration. Emphasis will be on high-sensitivity low-noise photodetectors, tunable lasers, optical amplifiers, and on ultrafast devices for the generation, modulation and detection of optical signals.     

Micro-Raman spectroscopy for characterization of semiconductor devices

Selected examples of the usefulness of micro-Raman spectroscopy for the analysis of semiconductor devices are discussed. This includes the determination of local temperatures in devices under operational conditions, built-in strain in processed silicon, and local crystal orientation.     

A self-consistent analysis of semiconductor laser rate equations for system simulation purpose

A procedure for extraction of the rate-equation parameters of semiconductor laser diodes is presented. Using small signal measurements, we have formulated a complete set of equations, which can be resolved analytically to obtain a solution for a combination of parameters that constitute a modified rate-equation model and is presented here for the first time. The proposed method does not necessitate at, or below threshold measurements, which require high sensitivity from the measuring equipment. Furthermore, without the need for any optimization, the solution to the rate equations is completely self-consistent since the parameters are linked together through functional relationships. With this new method, the determination of all the necessary rate-equation parameters to carry out large signal simulation is exclusive of the measurements for signal chirp, and as such computation of the chirp parameter is not included here. Comparison between large signal measurements and simulations from the computed parameters show very good agreement for a range of above threshold bias currents.     

The self-consistent single-particle model in nuclear physics

The nuclear many body problem is treated in the single particle approximation, i.e. on the basis of the Hartree-Fock-Bogolyubov approximation. Results of various applications are presented and discussed with emphasis on properties of rotational states of deformed nuclei.     

Conductance of small semiconductor devices

We calculate low field conductivity and mobility as a function of a sample length for small semiconductor samples. When the sample length is much smaller than the mean free path the current density is proportional to the applied voltage so that the apparent low field mobility is proportional to the device length. Calculation of the apparent low field mobility for high mobility GaAs devices shows that the size effects may be important for sample lengths smaller than 2 μm.     

Electric-field dependence of the intersubband optical absorption in a semiconductor quantum well

We present theoretical results of intersubband linear optical absorption in the conduction band of a GaAsAlGaAs quantum well with an applied electric field taking into account the field dependent linewidth. Our analysis is based on the one electron density matrix formulation with intrasubband relaxation processes due to polar optical phonon scattering and tunneling of electrons. We show that (a) for an increasing electric field the absorption peak corresponding to the transition of states 1 → 2 is shifted higher in energy and (b) the peak amplitude increases if the Fermi level is fixed and decreases if the electron density in the well is fixed when an increasing electric field is applied. The linewidth broadening also reduces the peak absorption amplitude.     

基于石墨烯的半导体光电器件研究进展

石墨烯自从被发现以来,由于其零带隙、低电导率、常温下的高电子迁移率及量子霍尔效应和独特的光吸收等优良特性,引发了世界各国科研人员的重视,研究人员对其物理性质及应用的研究越来越多并且进展迅速．本文以光纤通信用光电器件中的探测器、调制器为主,综述了石墨烯在光电探测器、调制器以及超快锁模激光器和用于发光二级管、触摸屏透明导电薄膜等方面的应用．     

Optical phonon sidebands of electronic intersubband absorption in strongly polar semiconductor heterostructures

We present the first evidence for a distinct optical phonon progression in the linear and nonlinear intersubband absorption spectra of electrons in a GaN/Al(0.8)Ga(0.2)N heterostructure. Femtosecond two-color pump-probe experiments in the midinfrared reveal spectral holes on different vibronic transitions separated by the LO-phonon frequency. These features wash out with a decay time of 80 fs due to spectral diffusion. The remaining nonlinear transmission changes decay with a time constant of 380 fs. All results observed are described by the independent boson model.