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1.
We investigated the hardness enhancement in titanium carbonitrides (TiCxN1−x) by the population analysis method based on first-principles calculations. Populations for bonds TiC and TiN in TiCxN1−x (0.25<x<0.75) are all positive. The enhanced hardness for titanium carbonitrides is well explained by overlap population analysis. Intrinsic hardness of TiCxN1−x has been calculated based on the obtained overlap populations. The calculated results are in good agreement with the available experimental data.  相似文献   

2.
The results of first-principles plane-wave-based pseudopotential method calculations of the elastic modulus, optical phonon modes, and polaron properties of zinc-blende Al1?xBxN are presented. Good agreement is obtained with the exciting experimental data for AlN and BN compounds. Our results provide predictions for the remaining mixed crystals Al1?xBxN (0 < x < 1) for which no direct experimental or theoretical data are presently available. The compositional dependence of features such as elastic constants and their related mechanical parameters, phonon frequencies, dielectric constants, and polaron parameters was investigated. The study may be useful for the characteristic analysis of AlBN-based quantum well devices.  相似文献   

3.
The surface and interface phonon-polaritons in freestanding rectangular quantum well wire systems consisting of polar ternary mixed crystals are investigated in the modified random-element-isodisplacement model and the Born–Huang approximation, based on the Maxwell's equations with the boundary conditions. The numerical results of the surface and interface phonon-polariton frequencies as functions of the wave-vector, geometric structure, and the composition of the ternary mixed crystals in GaAs/AlxGa1−xAs and ZnxCd1−xSe/ZnSe quantum well wire systems are obtained and discussed. It is shown that there are 10 and 8 branches of surface and interface phonon-polaritons in the two quantum well wire systems respectively. The effects of the “two-mode” and “one-mode” behaviors of the ternary mixed crystals on the surface and interface phonon-polariton modes are shown in the dispersion curves.  相似文献   

4.
The method for efficient separation of photoexcited carriers, based on the resonant tunneling phenomenon in the quantum well structure placed into the i-region of the p-i-n photovoltaic element, is proposed. The parameters of quantum well structures based on the GaAs/Ga1?x In x As system, implementing the mode of sequential resonant tunneling in the electric field of the GaAs p-i-n junction, is calculated. A microscopic model of resonant-tunneling transport in such structures is constructed, and the kinetic tunneling times are calculated depending on well and barrier parameters. The possibility of achieving sufficiently short (<~10 ps) tunneling times and, hence, quite efficient removal of photoelectrons and photoholes from quantum wells at a proper choice of barrier powers is shown.  相似文献   

5.
The composition and size of optically active CdxZn1−xSe/ZnSe quantum dots are estimated with a previously developed method. The results are then compared with those obtained for CdxZn1−xSe/Zn0.97Be0.03Se QDs. We show that introducing Be into the barrier material enhances both Cd composition and quantum size effect of optically active quantum dots.  相似文献   

6.
In order to design the optimal component structure of transmission-mode (t-mode) Ga1−xAlxN photocathode, the optical properties and quantum efficiency of Ga1−xAlxN photocathodes are simulated. Based on thin film principle, optical model of t-mode Ga1−xAlxN photocathodes is built. And the quantum efficiency formula is put forward. Results show that Ga1−xAlxN photocathodes can satisfy the need of detectors with “solar blind” property when the Al component is bigger than 0.375. There is an optimal thickness of Ga1−xAlxN layer to get highest quantum efficiency, and the optimal thickness is 0.3 μm. There is close relation between absorptivity and quantum efficiency, which is in good agreement with the “three-step” model. This work gives a reference for the experimental research on the Ga1−xAlxN photocathodes.  相似文献   

7.
Recent experimental investigations revealed that the biaxial stress in thin InGaN layers grown on thick GaN layer induces a large piezoelectric field along [0001] orientation that causes red-shift in optical transitions and reduction in oscillator strengths because of spatial separation of the electron and hole wave functions. In this Letter based on theoretical modeling we determined the well width z-dependent effect on red-shifted quantum-confined Stark effect (QCSE) in GaN/InxGa1 − xN (x=0.13) strained quantum well structures. Analyses are based on the solution of Schrödinger equation in a finite well including the internal piezoelectric electric field (F) due to the strained polarization as the perturbation potential. Our theoretical results show: (1) the red-shift in optical transition has a quadratic well-width form as it is for infinite wells (Davies, 1998) [1], (2) assuming the model based on a carrier effective mass dependence on the width of quantum wells, m(z), fits the experimental data (Takeuchi et al., 1997) [2] much more accurate compare to the model with constant effective mass, m.  相似文献   

8.
《Infrared physics》1987,27(6):407-410
In this work, analytical expressions determining the quantum efficiency at low electric fields, taking into account reflections at front and back detector surfaces and corresponding surface recombination velocities, are obtained.Using these expressions, the dependence of the quantum efficiency of Hg1−xCdxTe photoconductive detectors on the wavelength of the incident radiation for x = 0.215, at liquid nitrogen temperature, is calculated.  相似文献   

9.
We have calculated the spectral regime of subband transitions in AlxGa1−xN/GaN and AlxGa1−xN/InN single quantum wells. We used a simplified model to account for the internal electric fields, which modify the shape of the quantum well. Some of the parameters for these materials have not yet been firmly established. Therefore, we carried out the analysis for the extremes of the reported values of conduction band discontinuities and band gaps (in the case of InN). This analysis shows that the spectral regime of interband transitions for 1–4 nm thick wells has wavelengths above 0.5 μm for AlGaN/InN and above 0.8 μm for AlGaN/GaN and both heterostructures cover several μm wavelengths. The spectral variation with alloy composition is less pronounced in the AlxGa1−xN/InN single quantum wells due to the higher electric field present across the InN quantum well as compared to GaN. The results of these calculations are in good agreement with more rigorous theoretical approaches and available experimental values for AlxGa1−xN/GaN.  相似文献   

10.
In this paper, the effect of hydrostatic pressure on both the intersubband optical absorption coefficients and the refractive index changes is studied for typical GaAs/Al x  Ga1?x As cubic quantum dot. We use analytical expressions for the linear and third-order nonlinear intersubband absorption coefficients and refractive index changes obtained by the compact-density matrix formalism. The linear, third-order nonlinear, and total intersubband absorption coefficients and refractive index changes are calculated at different pressures as a function of the photon energy with known values of box length (L), the incident optical intensity (I), and Al concentration (x). According to the results obtained from the present work, we have found that the pressure plays an important role in the intersubband optical absorption coefficient and refractive index changes in a cubic quantum dot.  相似文献   

11.
12.
The size-quantized spectrum of a film (quantum well) with a variable band gap based on Pb1?x Sn x Se compounds has been studied. It is shown that an asymmetric modulation of the band gap in the film growth direction leads to the spin splitting of the electron subbands of a uniform quantum well. The effect of the state of the film surface on spontaneous polarization of the electron gas is discussed.  相似文献   

13.
We report a reflectance study on series of shallow quantum wells GaAs/AlxGa1−xAs types with different aluminium concentration. The observed barrier exciton reflectance line shape depends strongly on the shift in aluminium concentration in the two barriers, with the appropriate choice of the cap layer thickness. This observation was based on the reflectivity line shape analysis of anti-Bragg structures.  相似文献   

14.
In this paper, the third-harmonic generation (THG) in GaAs/Ga1 ? xAlxAs ridge quantum wires is studied in detail. An analytic expression for the THG is obtained using a compact density matrix approach and an iterative procedure. Numerical calculations are performed for the typical GaAs/Ga1 ? xAlxAs ridge quantum wire. The results show that the maximum THG over 10? 9? m2?/V2? can be obtained. Another important point is that the structural parameters have great influence on the THG in this system.  相似文献   

15.
The T-x magnetic phase diagram of Mn1 ? x Fe x Si solid solutions is probed by magnetic susceptibility, magnetization and resistivity measurements. The boundary limiting phase with short-range magnetic order (analogue of the chiral liquid) is defined experimentally and described analytically within simple model accounting both classical and quantum magnetic fluctuations together with effects of disorder. It is shown that Mn1 ? x Fe x Si system undergoes a sequence of two quantum phase transitions. The first “underlying” quantum critical (QC) point x* ~ 0.11 corresponds to disappearance of the long-range magnetic order. This quantum phase transition is masked by short-range order phase, however, it manifests itself at finite temperatures by crossover between classical and quantum fluctuations, which is predicted and observed in the paramagnetic phase. The second QC point x c ~ 0.24 may have topological nature and corresponds to percolation threshold in the magnetic subsystem of Mn1 ? x Fe x Si. Above x c the short-range ordered phase is suppressed and magnetic subsystem becomes separated into spin clusters resulting in observation of the disorder-driven QC Griffiths-type phase characterized by an anomalously divergent magnetic susceptibility χ ~ 1/T ξ with the exponents ξ ~ 0.5–0.6.  相似文献   

16.
Formulas are presented to calculate the heating of charge carriers and the generation of nonequilibrium phonons by intense photoexcitation of quantum-well heterostructures. It is shown that the deviations from thermal equilibrium are more pronounced for quasi-two-dimensional structures than for bulk material. Supporting experimental data are given on an MO-CVD AlxGa1-xAs-GaAs heterostructure consisting of a large GaAs quantum well (Lz ~ 200 Å) coupled to a phonon-generating array of seven small GaAs quantum wells (Lz ~ 50 Å).  相似文献   

17.
We report results of the high frequency (60 GHz) electron spin resonance (ESR) study of the quantum critical metallic system Mn1 ? x Fe x Si. The ESR is observed for the first time in the concentration range 0 < x < 0.24 at temperatures up to 50 K. The application of the original experimental technique allowed carrying out line shape analysis and finding full set of spectroscopic parameters, including oscillating magnetization, line width and g factor. The strongest effect of iron doping consists in influence on the ESR line width and spin relaxation is marked by both violation of the classical Korringa-type relaxation and scaling behavior. Additionally, the non-Fermi-liquid effects in the temperature dependence of the ESR line width, which may be quantitatively described in the theory of Wölfle and Abrahams, are observed at quantum critical points x* ~ 0.11 and x c ~ 0.24.  相似文献   

18.
Temperature and magnetic field dependences of the resistivity and Hall coefficient in layered single-crystal Nd2?xCexCuO4 (x = 0.12) films are experimentally investigated and analyzed. It is shown that this material clearly exhibits quantum effects characteristic of 2D semiconductor structures: negative magnetoresistance caused by suppression of the interference quantum correction by a magnetic field, a near-logarithmic temperature dependence of the conductivity, and a temperature dependence of the Hall coefficient related to e-e interaction. It is shown that, when analyzing experimental data, it is necessary to take interlayer transitions into account. Such an approach provides quantitative agreement between experiment and the standard theory of quantum corrections.  相似文献   

19.
In this work we are particularly interested for GaAs/Ga1−xAlxAs V-groove quantum wires. The paper presents an efficient and simple method for energy spectra and wave function calculations of electrons and holes in V-groove quantum wires. The method is based on the coordinate transformation of the V-groove quantum wire structure and the computational domain using a function proposed by Inoshita. Then, the Hamiltonian followed by implementation of the FDM (Finite Difference Method) in the new computational space leads to an eigenvalues problem resolved using specialized LAPACK’s routines. The influence of the parameters introduced in the mathematical function, is studied on the energy levels of electrons and holes as well as the oscillator strengths.  相似文献   

20.
Experimental results on high electric field longitudinal transport in GaAs/AlAs and GaAs/Ga1-xAlxAs multiple quantum wells (MQW) are presented and compared with the prediction of a dielectric continuum model. We draw from our experiments the following four conclusions.(i) In GaAs/Ga1-xAlxAs systems the dominant energy and momentum relaxation mechanism is through scattering with GaAs -modes.(ii) However, in GaAs/AlAs systems the AlAs interface mode is dominant in relaxing the energy and momentum of the quantum well electrons.(iii) The hot electron momentum relaxation as obtained from the high-field drift velocity experiments is strongly affected by the production of hot phonons as expected from a model involving a non-drifting hot phonon distribution.(iv) The importance of the AlAs interface mode in GaAs/Ga1-xAlxAs MQW is not the result of the intrinsic scattering rate but related to its shorter lifetime, compared to GaAs modes.  相似文献   

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