Observation of confined states in anIn0.53Ga0.47As/In0.52Al0.48Asmulti-quantum wells structure by quantum confined Stark effects

Photocurrent spectra in an In_0.53Ga_0.47As /In_0.52Al_0.48As multi-quantum wells structure containing 9.4 nm wide wells were measured at room temperature in electric fields. The exciton peaks of ground-state transitions shifted fairly in 167 kV cm ^− 1as the quantum confined Stark effect. Stark shifts were calculated by using the Runge–Kutta method using the effective mass equation with our experimental band parameters. Our parameters are the hole effective masses and valence band offset derived from saturation of a highest eigen energy, electron effective mass depending on energies and the conduction band offset derived from observed quantum number. It was possible to sufficiently use our experimental band parameters for the calculation of the Stark shift in the electric field.     

Classical and quantum hall effect measurements in GaInNAs/GaAs quantum wells

We have performed magneto-transport experiments in modulation-doped Ga_0.7In_0.3N_yAs_1−y/GaAs quantum wells with nitrogen mole fractions 0.4%, 1.0% and 1.5%. Classical magnetotransport (resistivity and low-field Hall effect) measurements have been performed in the temperatures between 1.8 and 275 K, while quantum Hall effect measurements in the temperatures between 1.8 and 47 K and magnetic fields up to 11 T.The variations of Hall mobility and Hall carrier density with nitrogen mole fractions and temperature have been obtained from the classical magnetotransport measurements. The results are used to investigate the scattering mechanisms of electrons in the modulation-doped Ga_0.7In_0.3N_yAs_1−y/GaAs quantum wells. It is shown that the alloy disorder scattering is the major scattering mechanism at investigated temperatures.The quantum oscillations in Hall resistance have been used to determine the carrier density, effective mass, transport mobility, quantum mobility and Fermi energy of two-dimensional (2D) electrons in the modulation-doped Ga_0.7In_0.3N_yAs_1−y/GaAs quantum wells. The carrier density, in-plane effective mass and Fermi energy of the 2D electrons increases when the nitrogen mole fraction is increased from y=0.004 to 0.015. The results found for these parameters are in good agreement with those determined from the Shubnikov-de Haas effect in magnetoresistance.     

Magnetotransport in modulation-doped In0.53Ga0.47As/In0.52Al0.48As heterojunctions: in-plane effective mass,quantum and transport mobilities of 2D electrons

Shubnikov–de Haas (SdH) and Hall effect measurements, performed in the temperature range between 3.3 and 20 K and at magnetic fields up to 2.3 T, have been used to investigate the electronic transport properties of lattice-matched In_0.53Ga_0.47As/In_0.52Al_0.48As heterojunctions. The spacer layer thickness (t_S) in modulation-doped samples was in the range between 0 and 400 Å. SdH oscillations indicate that two subbands are already occupied for all samples except for that witht_S =  400 Å. The carrier density in each subband, Fermi energy and subband separation have been determined from the periods of the SdH oscillations. The in-plane effective mass (m ^* ) and the quantum lifetime (τ_q) of 2D electrons in each subband have been obtained from the temperature and magnetic field dependences of the amplitude of SdH oscillations, respectively. The 2D carrier density (N₁) in the first subband decreases rapidly with increasing spacer thickness, while that (N₂) in the second subband, which is much smaller thanN₁ , decreases slightly with increasing spacer thickness from 0 to 200 Å. The in-plane effective mass of 2D electrons is similar to that of electrons in bulk In_0.53Ga_0.47As and show no dependence on spacer thickness. The quantum mobility of 2D electrons is essentially independent of the thickness of the spacer layer in the range between 0 and 200 Å. It is, however, markedly higher for the samples with a 400 Å thick spacer layer. The quantum mobility of 2D electrons is substantially smaller than the transport mobility which is obtained from the Hall effect measurements at low magnetic fields. The transport mobility of 2D electrons in the first subband is substantially higher than that of electrons in the second subband for all samples with double subband occupancy. The results obtained for transport-to-quantum lifetime ratios suggest that the scattering of electrons in the first subband is, on average, forward displaced in momentum space, while the electrons in the second subband undergo mainly large-angle scattering.     

Contactless electroreflectance spectroscopy of Ga(In)NAs/GaAs quantum well structures containing Sb atoms

Contactless electroreflectance (CER) spectroscopy has been applied to investigate the optical transitions in Ga(In)NAs/GaAs quantum well (QW) structures containing Sb atoms. The identification of the optical transitions has been carried out in accordance with theoretical calculations which have been performed within the framework of the effective mass approximation. Using this method, the bandgap discontinuity for GaN_0.027As_0.863Sb_0.11/GaAs, Ga_0.62In_0.38As_0.954N_0.026Sb_0.02/GaAs, and Ga_0.61In_0.39As_0.963N_0.017Sb_0.02/GaN_0.027As_0.973/GaAs QW structures has been determined. It has been found that the conduction-band offset is ∼50 and ∼80% for GaN_0.027As_0.863Sb_0.11/GaAs and Ga_0.62In_0.38As_0.954N_0.026Sb_0.02/GaAs QWs, respectively. It corresponds to 264 and 296 meV depth QW for electrons and heavy-holes in GaN_0.027As_0.863Sb_0.11/GaAs QW; and 520 and 146 meV depth QW for electrons and heavy-holes in Ga_0.62In_0.38As_0.954N_0.026Sb_0.02/GaAs QW. In the case of the Ga_0.61In_0.39As_0.963N_0.017Sb_0.02/GaN_0.027As_0.973/GaAs step-like QW structure it has been shown that the depth of electron and heavy-hole Ga_0.61In_0.39As_0.963N_0.017Sb_0.02/GaN_0.027As_0.973 QW is ∼144 and ∼127 meV, respectively.     

Photoionization cross-section and binding energy of shallow donor impurities in Ga1−xInxNyAs1−y/GaAs quantum wires

We have investigated the effects of the nitrogen and indium concentrations on the photoionization cross-section and binding energy of shallow donor impurities in Ga_1−xIn_xN_yAs_1−y/GaAs quantum wires. The numerical calculations are performed in the effective mass approximation, using a variational method. We observe that incorporation of small amounts of nitrogen and indium leads to significant changes of the photoionization cross-section and binding energy.     

Influence of quantization of band states on the effective electron mass in quaternary alloys

Summary An attempt is made to study the effective electron mass in quaternary alloys, taking a In_1−x Ga _x As _y P_1−y lattice matched to InP, by using the three-band Kane model under different physical conditions,e.g. bulk specimens, magnetic quantization, cross-field configuration, quantum well, electric-field-aided quantum well, magnetic-field-aided quantum well, quantum well under cross fields, quantum well wires, electric-field-aided quantum well wires, magnetic-field-aided quantum well wires and quantum well wires under cross fields by formulating the respective expressions. We have plotted the effective Fermi level mass with various physical variables under different conditions. In the presence of a quantizing magnetic field the effective mass depends on the spin splitting of Landau levels due to the spin-orbit splitting parameter of the valence bands. Under cross-field configuration and the various quantum confined low-dimensional systems, the effective masses depend on the respective quantum numbers in addition to the Fermi energies even for parabolic models because of the inherent features of such systems. In addition, the corresponding results for relatively wide-gap materials have also been obtained from our generalized formulations under certain limiting conditions.     

Effect of barrier configuration on excitonic recombination in Ga.47In.53As/Al.48In.52As multi quantum well structures

Photoluminescence and photoluminescence excitation spectroscopy on Ga_.47In_.53As multi quantum wells confined either by homogenous ternary Al_.48In_.52As barriers or by Ga_.47In_.53As/Al_.48In_.52As short-period superlattice (SPS) barriers show that the confinement by SPS barriers improves the edge luminescence significantly. The spectral width of the free-exciton absorption and the low-temperature emission peak as well as the Stokes-shift between emission and excitation spectra are reduced as compared to samples clad by homogenous ternary Al_.48In_.52As barriers. Based on temperature-dependent emission and excitation measurements, the dominant low-temperature emission line in the SPS-clad Ga_.47In_.53As multi quantum wells is assigned to intrinsic excitonic recombination.     

Design of strain-compensated In x Ga1-x As/In y Al1-y As quantum cascade laser structures towards the shorter wavelengths

We design the In _x Ga_1-x As/In_yAl_1-yAs quantum cascade laser (QCL) structures, based on the four-quantum well active region with vertical transition with strain compensation towards the shorter wavelengths, operating at λ ~2.93–6.6μm. Considering the objective function related to the optical gain, i.e., ${z_{43}^2 (1-\tau_3 /\tau_{43})\tau_4}$ , and the escape energy related to the carrier leakage to continuum, the design of QCLs is carried out in double infinite feedback loops. Each barrier/well layer in the active region is optimized towards the lasing wavelength as short as possible under a properly designed injector. For efficient short wavelength emission, the larger conduction band discontinuity (ΔE _c ) is achieved by changing the indium mole fractions of strain-compensated In _x Ga_1-x As/In_yAl_1-y As layers. The experimentally verified injectors are properly modified for the stronger coupling between the wavefunctions of the ground state in injector and the upper state in active region. Thus the use of strain-compensated In_0.72Ga_0.28As/In_0.3Al_0.7As structure (i.e., ΔE _c = 857 meV) leads to the shortest wavelength up to λ ~2.93μm with τ ₄₃ = 2.13 ps, τ ₄ = 0.87 ps, τ ₃ = 1.43 ps and z ₄₃ = 1.03 nm under an electric field of 96 kV/cm.     

Threshold electrical switching in As45Te55-xInx and As50Te50-xInx glasses

The electrical switching behaviour of As₄₅Te_55-xIn_x (5≤x≤15) and As₅₀Te_50-xIn_x (2.5≤x≤11.5) has been studied over a wide range of compositions. These glasses are found to exhibit threshold switching. The composition dependence of switching voltage (V_t) has been found to exhibit a change in slope and a local minimum at compositions x=10 and 12.5 for As₄₅Te_55-xIn_x and x=7.5 and 10.8 for As₅₀Te_50-xIn_x, respectively. The slope change in V_t verses x and the local minimum have been identified using two network topological effects, namely the rigidity percolation threshold and the chemical threshold. Received: 23 August 2001 / Accepted: 27 August 2001 / Published online: 11 February 2002     

1.55μm InGaAsP/InP应变量子阱激光器的LP－MOCVD生长

本文首次报导了生长温度为550℃,以三甲基镓(TMGa)和三甲基铟(TMIn)为Ⅲ族源,用低压金属有机物气相沉积(LFMOCVD〕技术,高质量1.62um和1.3umInGaAsP及In_0.57Ga_0.43As_0.98P_0.04/In_0.73Ga_0.27As_0.6P_0.4量子阶结构的生长,并给出了1.55umGaAsP/InP分别限制应变量子阱结构激光器的生长条件,激光器于室温下脉冲激射,其阈值电流密度为2.4kA/cm².     

Energy sublevels in an Al0.5Ga0.5As/GaAs/Al0.5Ga0.5As quantum wire

We report the successful fabrication of a V-grooveAl_0.5Ga_0.5As/GaAs/Al_0.5Ga_0.5As quantum wire system and the temperature-dependent photoluminescence (PL) measurement. The PL spectra are dominated by four features at 681, 642, 635 and 621 nm attributed to the luminescences from quantum wire, top, vertical and side-wall well regions by micro-PL measurements. By the calculations of the energy structure, discrete states (localized sublevels) in the quantum wire region and continuum states (extended along the side-wall and vertical quantum wells) in side-wall and vertical quantum wells have been obtained in both the conduction and valence bands. The calculated excitation energies explain very well the peak positions and their temperature dependence in the photoluminescence measurements.     

Band edge offsets in strained (InGa)As-(AlGa)As heterostructures

The excitonic transitions between the ground electron and hole quantum well sublevels in strained In_xGa_1-xAs-Al_yGa_1-yAs multiple quantum well structures (x = 0.12−0.35 and y = 0.2−0.35) have been investigated by means of photoluminescence and photoconductivity measurements. The molecular beam epitaxy grown structures contained an Al_yGa_1-yAs matrix with one unstrained GaAs and three strained In_xGa_1-xAs quantum wells one of which was in the GaAs cladding layers. The ratio of the conduction band edhe line up to the band gap offset for the strained In_xGa_1-xAs-unstrained Al_yGa_1-yAs interface has been found to be 0.67 ± 0.08 for the studied regions of x and y.     

Investigation of barrier tunneling characteristics of symmetrical double quantum well in In0.25Ga0.75As/GaAs/In0.25Ga0.75As heterostructure

The optical and electrophysical properties of the GaAs/In_0.25Ga_0.75As heterostructure with a symmetric double quantum well have been investigated. The influence of tunneling electrons and holes through an internal barrier of the quantum well on the shift and splitting of the quantum levels is analyzed. The theoretical estimates are compared with the results of the photoluminescence and photoconductivity measurements. The Hall measurements indicate that the barrier strongly affects the mobility of charge carriers.     

Quantum lifetimes and momentum relaxation of electrons and holes in Ga0.7In0.3N0.015As0.985/GaAs quantum wells

Electronic transport in n- and p-type modulation-doped Ga_0.7In_0.3N_0.015As_0.985/GaAs quantum wells are investigated using magneto-transport measurements in the temperature range between T?=?1.8 and 32?K and at magnetic fields up to B?=?11?T. The momentum relaxation and the quantum lifetimes (τ_q ) of electrons and holes are obtained directly from the temperature and magnetic field dependencies of the SdH oscillation amplitudes, respectively. A detailed analysis of quantum and transport life times indicates that the momentum relaxation of holes is forward displaced in k-space, while a large angle-scattering mechanism is prominent for the electrons. This discrepancy is believed to be due to scattering of electrons with nitrogen complexes and to the lack of such a mechanism for holes.     

Momentum conservation in the luminescence of modulation-doped Ga x In1−x As−Al y In1−y As quantum wells

Summary Thek-conserving selection rule in the electron-hole recombination is investigated by intensity-dependent photoluminescence measurements inn-type modulation-doped Ga _x In_1−x As−Al _y In_1−y As single quantum wells intentionally doped with Be acceptors in the well centre. Thek-non-conserving recombination process involves electrons with momentum up to the Fermi edge and holes localized on the Be acceptors. The transition from a one-component electron plasma to a two-component electron-hole plasma is studied by comparing the experimental results with theoretical line shape models. The density-dependent band gap renormalization is determined for the one-component and the two-component electron-hole plasma. The obtained results are found to agree well with recent theoretical calculations.     

Thermal transport through a one-dimensional quantum spin-1/2 chain heterostructure: The role of three-site spin interaction

The electron effective masses in n-type modulation doped Ga_0.7In_0.3N _y As_1?y /GaAs quantum wells with nitrogen mole fractions of y = 0.004 and 0.010 were investigated experimentally. Two experimental techniques: magnetic field dependent photoluminescence measurements and phonon-plasmon coupled-mode line-shape analysis of vibrational spectroscopy measurements, were employed in the investigations. In the first technique, the effective masses of the electrons have been determined from the diamagnetic energy shift dependencies up to 11 T. The vibrational properties of the samples were studied using Raman scattering spectroscopy at room temperature. The effective masses obtained from both two techniques are in good agreement with the current results in the literature.     

Stokes shift in one-side modulation-n-doped-strained GaxIn1 − xAs/InP asymmetric quantum well

The effects of strain on the Stokes shift in one-side modulation-dopedGa_xIn_1 − xAs /InP asymmetric quantum wells (AQWs) are systematically investigated. By making use of a self-consistent Poisson–Schrödinger solver in the frame of a finite difference method, the quasi-Fermi levels and the band bending are determined under the effective mass approximation. The central-zone valence-band structures for compressively strained and tensile strained AQWs were calculated by making use of a four-band Luttinger–Kohn Hamiltonian. It was found that the strain influences the relative positions of the heavy-hole HH₁and the light-hole LH₁subbands and that the Stokes shifts are greatly reduced by tensile strain in the case of a Ga_0.6In_0.4As /InP AQW. Moreover, it was found that due to the presence of the two-dimensional electron gas the Stokes shifts in AQWs are much larger than the corresponding ones for a square quantum well. Also, the variation of the Stokes shift with spacer layer width for compressively strained AQWs was found to be more rapid than that for tensile strained AQWs.     

Electron mobilities in isomorphic In0.53Ga0.47As quantum wells on InP substrates

The influence of the doping level, illumination, and width of isomorphic In_0.52Al_0.48As/In_0.53Ga_0.47As/In_0.52Al_0.48As quantum wells grown on InP substrates on the electron mobility is studied. The persistent photoconductivity at low temperatures is found. Band diagrams are calculated and optimal parameters are found for obtaining the maximum electron mobility. The quantum and transport electron mobilities in dimensional quantization subbands are obtained from the Shubnikov-de Haas effect. The electron mobilities are calculated in dimensional quantization subbands upon scattering by ionized impurities taking intersubband transitions into account. Scattering by ionized impurities in samples studied is shown to be dominant at low temperatures.     

Multiphonon absorption in As2S3As2Se3 glasses

Multiphonon absorption in As₂S₃ and As₂Se₃ glasses is well explained by a molecular model in terms of combination bands of high frequency vibrational modes of pyramidal AsY₃ and bent AsYAs groups (Y = SorSe). Multiphonon absorption coefficients in mixed As₂S₃As₂Se₃ glasses are nearly additive in terms of the pure components, suggesting a high degree of non-random mixing.     

Interband emission energy in a dilute nitride quaternary semiconductor quantum dot for longer wavelength applications

Excitonic properties are studied in a strained Ga_1−xIn_xN_yAs_1−y/GaAs cylindrical quantum dot. The optimum condition for the desired band alignment for emitting wavelength 1.55 µm is investigated using band anticrossing model and the model solid theory. The band gap and the band discontinuities of a Ga_1−xIn_xN_yAs_1−y/GaAs quantum dot on GaAs are computed with the geometrical confinement effect. The binding energy of the exciton, the oscillator strength and its radiative life time for the optimum condition are found taking into account the spatial confinement effect. The effects of geometrical confinement and the nitrogen incorporation on the interband emission energy are brought out. The result shows that the desired band alignment for emitting wavelength 1.55 µm is achieved for the inclusion of alloy contents, y=0.0554% and x=0.339% in Ga_1−xIn_xN_yAs_1−y/GaAs quantum dot. And the incorporation of nitrogen and indium shows the red-shift and the geometrical confinement shows the blue-shift. And it can be applied for fibre optical communication networks.