Calculation of Valence Subband Structures for Strained Quantum-Wells by Plane Wave Expansion Method Within 6 * 6 Luttinger-Kohn Model

The valence subband energies and wave functions of a tensile strained quantum well are calculated by the plane wave expansion method within the 6 * 6 Luttinger-Kohn model. The effect of the number and period of plane-waves used for expansion on the stability of energy eigenvalues is examined. For practical calculation, it should choose the period large sufficiently to ensure the envelope functions vanish at the boundary and the number of plane waves large enough to ensure the energy eigenvalues keep unchanged within a prescribed range.

Observations on subband electron properties in In0.65Ga0.35As/In0.52Al0.48As MM-HEMT with Si delta-doped on the barriers

Magneto-transport measurements have been carried out on a Si delta-doped In0.65Ga0.35As/In0.52Al0.48As metamorphic high-electron-mobility transistor with InP substrate in a temperature range between 1.5 and 60 K under magnetic field up to 13 T. We studied the Shubnikov-de Haas (SdH) effect and the Hall effect for the In0.65Ga0.35As/In0.52Al0.48As single quantum well occupied by two subbands and obtained the electron concentration and energy levels respectively. We solve the Schrodinger-Kohn-Sham equation in conjunction with the Poisson equation self-consistently and obtain the configuration of conduction band, the distribution of carriers concentration, the energy level of every subband and the Fermi energy. The calculational results are well consistent with the results of experiments. Both experimental and calculational results indicate that almost all of the delta-doped electrons transfer into the quantum well in the temperature range between 1.5 and 60 K.

Quantum master equation scheme of time-dependent density functional theory to time-dependent transport in nanoelectronic devices

In this work a practical scheme is developed for the first-principles study of time-dependent quantum transport. The basic idea is to combine the transport master equation with the well-known time-dependent density functional theory. The key ingredients of this paper include (i) the partitioning-free initial condition and the consideration of the time-dependent bias voltages which base our treatment on the Runge-Gross existence theorem; (ii) the non-Markovian master equation for the reduced (many-body) central system (i.e., the device); and (iii) the construction of Kohn-Sham master equations for the reduced single-particle density matrix, where a number of auxiliary functions are introduced and their equations of motion (EOMs) are established based on the technique of spectral decomposition. As a result, starting with a well-defined initial state, the time-dependent transport current can be calculated simultaneously along with the propagation of the Kohn-Sham master equation and the EOMs of the auxiliary functions.

Theoretical analysis of the bandgap for the intermixed GaInP/AlGaInP quantum wells

Compositional distribution of the quantum well and barrier after quantum well intermixing for GaInP/AlGaInP system was theoretically analyzed on the basis of atom diffusion law. With the compositional distribution result, the valence subband structure of the intermixed quantum well was calculated on the basis of 6x6 Luttinger-Kohn Hamiltonian, including spin-orbit splitting effects. TO get more accurate results in the calculation, a full 6-band problem was solved without axial approximation, which had been widely used in the Luttinger-Kohn model to simplify the computational efforts, since there was a strong warping in the GaInP valence band. At last, the bandgap energy of the intermixed quantum well was obtained and the calculation result is of much importance in the analysis of quantum well intermixing experiments.

Calculation of valence subband structures for strained GaInP/AlGaInP quantum wells without axial approximation

Usually in the calculation of valence subband structure for III-V direct bandgap material, axial approximation had been used in the Luttinger-Kohn model to simplify the computational efforts. In this letter, the valence subband structure for the GaInP/AlGaInP strained and lattice-matched quantum wells was calculated without axial approximation, on the basis of 6x6 Luttinger-Kohn Hamiltonian including strain and spin-orbit splitting effects. The numerical simulation results were presented with help of the finite-difference methods. The calculation results with/without axial approximation were compared and the effect of axial approximation on the valence subband structure was discussed in detail. The results indicated that there was a strong warping in the GaInP valence band, and axial approximation can lead to an error when k was not equal to zero, especially for compressively strained and lattice-matched GaInP/AlGaInP quantum wells.

Design and fabrication of polarization-insensitive 1550 mm semiconductor optical amplifiers

Polarization-insensitive semiconductor optical amplifiers (SOA's) with tensile-strained multi-quantum-wells as actice regions are designed and fabricated. The 6x6 Luttinger-Kohn model and Bir-Pikus Hamiltonian are employed to calculate the valence subband structures of strained quantum wells, and then a Lorentzian line-shape function is combined to calculate the material gain spectra for TE and TM modes. The device structure for polarization insensitive SOA is designed based on the materialde gain spectra of TE and TM modes and the gain factors for multilayer slab waveguide. Based on the designed structure parameters, we grow the SOA wafer by MOCVD and get nearly magnitude of output power for TE and TM modes from the broad-area semiconductor lasers fabricated from the wafer.

地幔压力下CaSiO3 Perovskite状态方程和弹性常数的第一性原理研究

In the past decade density functional theory (DFT) has made its way from a peripheral position in quantum chemistry to center. Of course the often excellent accuracy of the DFT based methods has provided the primary driving force of this development. This dissertation is devoted to the study of physical and chemical properties of planetary materials by first-principle calculation. The concerned properties include the geometry, elastic constants and anisotropy. In the first chapter, we give a systematic introduction to theoretical background and review its progress. Development of quantum chemistry promotes the establishment of DFT. Theorem of Hohenberg-Kohn is the fundament of DFT and is developed to Kohn-Sham equation, which can be used to perform real calculations. Now, new corrections and extensions, together with developed exchange-correlation, have made DFT more accurate and suitable for larger systems. In the second chapter, we focus on the calculational methods and technical aspects of DFT. Although it is important to develop methods and program, external package are still often used. At the end of this chapter, we briefly some widely used simulation package and the application of DFT. In the third chapter, we begin to focus on properties of real materials by first principles calculation. We study a kind of minerals named Ca perovskite, investigate its possible structure and anisotropy at Earth’s mental condition. By understanding and predicting geo-physically important materials properties at extreme conditions, we can get the most accurate information to interpret seismic data in the context of likely geophysical processes.

高温高压下钠长石熔体结构及水的溶解机理实验研究

通过对高温高压下钠长石熔体结构及水在钠长石熔体中溶解机制的Raman和FTIR光谱实验研究，可以得出以下结论：（1）随着压力升高（1bar-2.0GPa）NaAlSi_3O_8熔体玻璃Raman光谱的低频区（50-650cm~(-1)）不断变窄并向高频方向移动，同时高频区（850-1300cm~(-1)）不断变窄且向低频区方向移动，这表明随着压力升高T-O-T为（T = Si, Al）键角（0）不断减小，并且分布范围变窄，T－O－T键角这种变化从而可使T－O键的力常数减小，导致键强减弱，另外，580cm~(-1)谱峰强度随着压力升高不断减弱，并在0.8-1.0GPa时最为显著，这是由于在0.8-1.0GPa时包含（Si, Al）的平面三元环结构的“垮塌“造成的。此外，钠长石熔体结构随压力升高的这种变化特征与对其粘度的研究是相符的；（2）水在钠长石熔体中同时以OH和H_2O形式存在，这分别对应于FTIR光谱中的4500cm~(-1)及5200cm~(-1)谱峰。根据对水在钠长石熔体中溶解类型的红外光谱研究以及热力学计算都表明，在溶解初期水主要以OH存在于熔体中，此时H_2O含量相对较低；随着熔体中水含量的升高，OH所占比例越来越低，而H_2O分子则成为主要的溶解类型；（3）根据对含水钠长石玻璃的Raman和FTIR光谱研究，并结合Kohn等的MAS NMR结果，认为H_2O在NaAlSi_3O_8熔体中的溶解作用同时存在两种机制：一方面H_2O与Al-O°-Al 结构单元反应发生解聚作用而生成Q~3 Al-OH，并造成Raman光谱中900cm~(-1)谱峰的出现；另一方面水中的H~+与钠长石熔体中的Na~+发生转换作用成为电荷平衡离子。水在钠长石熔体中的溶解作用可表示为：H_2O + 3NaAlSi_3O_8 = 2NaAl(OH)Si_3O_(7.5) + HAlSi_3O_8 + NaOH 考虑到水在熔体中的溶解类型与水含量的关系以及熔体粘度的变化，在溶解初期水的溶解机制以生成Al-OH为主，随着水含量的升高，H~+与Na~+之间的置换作用变得愈加重要。