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.     

Theoretical investigation of the conduction and valence band offsets of GaAs1−x Nx/GaAs1−yNy heterointerfaces

Theoretical investigations of the conduction band offset (CBO) and valence band offset (VBO) of the relaxed and pseudo-morphically strained GaAs_1−xN_x/GaAs_1−yN_y heterointerfaces at various nitrogen concentrations (x and y) within the range 0-0.05 and along the [0 0 1] direction are performed by means of the model-solid theory combined with the empirical pseudopotential method under the virtual crystal approximation that takes into account the effects of the compositional disorder. It has been found that for y < x, the CBO and VBO have negative and positive signs, respectively, whereas the reverse is seen when y > x. The band gap of the GaAs_1−xN_x over layer falls completely inside the band gap of the substrate GaAs_1−yN_y and thus the alignment is of type I (straddling) for y < x. When y > x, the alignment remains of type I but in this case it is the band gap of the substrate GaAs_1−yN_y which is fully inside the band gap of the GaAs_1−xN_x over layer. Besides the CBO, the VBO and the relaxed/strained band gap of two particular cases: GaAs_1−xN_x/GaAs and GaAs_1−xN_x/GaAs_0.98N_0.02 heterointerfaces have been determined.     

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.     

Intermixing behavior in InGaAs/InGaAsP multiple quantum wells with dielectric and InGaAs capping layers

The influence of the InGaAs capping layer on the intermixing behavior of dielectric-capped In_0.53Ga_0.47 As/In_0.81Ga_0.19As_0.37P_0.63 multiple quantum wells (MQWs) was investigated by measuring the change in the photoluminescence spectra after rapid thermal annealing. The magnitude of the energy shift in the transition energy from the first electronic sub-band to the first heavy- and light-hole sub-bands of the MQWs is large when SiO₂ and InGaAs hybrid capping layers are employed, but it is rather small when Si₃N₄ and InGaAs hybrid capping layers are employed. This result indicates that the InGaAs capping layer holds promise for applications involved in the fabrication of integrated photonic devices, but only when it is incorporated with the SiO₂ capping layer. The reason why the InGaAs capping layer behaves differently under the SiO₂ and Si₃N₄ capping layers is also discussed. Received: 4 December 1999 / Accepted: 26 September 2000 / Published online: 10 January 2001     

Evidence by Raman scattering on In1−xGaxAsyP1−y of the two-mode behaviour of In1−xGaxP

We report the Raman scattering study of optical vibrations in indium rich In_1?xGa_xAs_yP_1?y epitaxial layers grown on InP. We evidence the splitting of the LO line of InP even for very small x and demonstrate it is due to the presence of gallium in the samples. These results lead us to ascribe to In_1?xGa_xP a somewhat modified two-mode behaviour and to In_1?xGa_xAs_yP_1?y a four-mode behaviour.     

Photoreflectance investigation of hydrogenated (InGa)(AsN)/GaAs heterostructures

The optical response of as grown and hydrogenated In_0.32Ga_0.68As_1-yN_y/GaAs single quantum wells (y = 0, 0.027) has been investigated from T = 80 K to room temperature by photoreflectance. Three excitonic spectral features detected in the N free sample shift to lower energy in the N containing sample and back to higher energy upon H irradiation of the N containing sample. In the hydrogenated sample, a progressive change with increasing temperature of the nature of the lowest energy transition from an excitonic to a band-to-band character has been explained in terms of an increasing release of carriers from traps formed by H and N clusters. A reduction in the oscillator strength of the lowest energy transition and an increase in the binding energy of the heavy-hole exciton have been explained in terms of an increase in the electron effective mass upon N introduction into the In_xGa_1-xAs lattice. Received 23 June 2002 Published online 19 November 2002     

Hot electron energy and momentum relaxation in GaAs/AlAs and GaAs/Ga1-xAlxAs multiple quantum wells

Experimental results on high electric field longitudinal transport in GaAs/AlAs and GaAs/Ga_1-xAl_xAs 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/Ga_1-xAl_xAs 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/Ga_1-xAl_xAs MQW is not the result of the intrinsic scattering rate but related to its shorter lifetime, compared to GaAs modes.     

Resonant enhancement (?) of the recombination probability at the nitrogen-trap, Γ-band edge crossover in GaAs1−xPx: N(EN = EΓ, x ≡ xN)

Previously it has been suggested on theoretical grounds and early data on N-doped In_1?xGa_xP that at the point of degeneracy of the Γ band edge and the N-trap (x ≡ x_N) the electron-hole recombination probability associated with the trap is resonantly enhanced by the presence of Γ band states. Data are presented on N-doped and N-free In_1?xGa_xP_1?zAs_z/ GaAs_1?yP_y (x ～ 0.70, y ≈ 0.40, z ～ 0.01) single heterojunction laser diodes fabricated on the same VPE GaAs_1?yP_y:N system, where the position of the N trap is well known, indicate that the N trap weakens the band-to-band (Γ) transition and is not itself enhanced beyond the usual band structure enhancement (BSE) described recently for ternary alloys. A theoretical argument is offered to explain the discrepancy between earlier theory and experimental observations.     

Photoreflectance spectroscopy of a Ga0.62In0.38N0.026As0.954Sb0.02/GaAs single quantum well tailored at 1.5 μm

Optical properties of a Ga_0.62In_0.38As_0.954N_0.026Sb_0.02/GaAs single quantum well (SQW) tailored at ∼1.5 μm have been investigated by photoreflectance (PR) spectroscopy. The identification of the optical transitions was carried out in accordance with theoretical calculations, which were performed within the framework of the usual envelope function approximation. Using this method, four confined states for both electrons and heavy holes have been found and the optical transitions between them have been determined. The obtained result corresponds to a conduction band offset ratio close to 80%. In addition, the effect of ex situ annealing has been investigated. Lineshape analysis of the PR transitions shows that one of the phenomena responsible for the blueshift of QW transitions is the change in the nitrogen nearest-neighbour environment from Ga-rich to In-rich environments.     

Wave function engineering in compressive- and tensile-strained laser structures

The engineering of the valence subbands for device applications has concentrated on the energy separation between heavy- and light-hole states. We show that the degree of overlap between the envelope functions of heavy- and light-hole states can affect the in-plane dispersion of the highest hole subband. We consider ways to reduce this overlap by spatially separating the heavy- and light-hole states to different layers, while maximizing their energy separation. Strain-compensated superlattices where opposite strains are introduced in the well and barrier regions offer such possibilities and lead to a significant increase of the optical gain in semiconductor lasers. We consider the In_xGa_1-xAs_yP_1-y /In_x'Ga_1-x'As_y'P_1-y' system grown on an InP substrate where the wells are under biaxial compression while the barriers are under tension. In this type of structures, the electron and heavy-hole states are confined to the compressive layers whereas the light-holes are confined to the tensile layers. We also discuss the possibility of confining light-hole and electron states to wells under tension, of potential benefit for lasers operating in the transverse magnetic (TM) mode.     

An attempt to design long-wavelength (>2 μm) InP-based GaInNAs diode lasers

In the present paper, anticipated performance characteristics of various InP-based GaInNAs quantum-well (QW) active regions are determined with the aid of our comprehensive computer model for various sets of parameters (temperature, carrier concentration, QW thickness). It is evident from this analysis that the compressively strained InP-based Ga_0.12In_0.88N_0.02As_0.98/Ga_0.275In_0.725As_0.6P_0.4 QW structure may offer expected lasing emission. Its maximal optical gain of over 2150 cm^?1 has been determined at room temperature for the wavelength of about 2815 nm for the QW thickness of 10 nm and the carrier concentration of 5×10¹⁸ cm^?3. Therefore, the above InP-based QW structure may be successfully applied in compact semiconductor laser sources of the desired radiation of wavelengths longer at room temperature than even 2800 nm. Similar GaAs-based devices emit radiation of distinctly shorter wavelengths, whereas GaSb-based ones avail themselves of more expensive substrates as well as exhibit lower thermal conductivities and worse carrier confinements.     

Self-consistent simulation of corrugated layered structures

An efficient self-consistent 2-D Schrödinger/Poisson solver, including shifted periodic boundary conditions, is used to obtain the wavefunctions and energy levels in the quantum wires formed at the corners of periodic saw-tooth structures consisting of layers of Al_1−xGa_xAs and GaAs materials. We find that the formation of a quantum wire at the corners of the GaAs layer is very sensitive to the physical parameters of the neighboring Al_1−xGa_xAs layers. Simple potential models yield solutions which are qualitatively very different from self-consistent results. Electron population build-up in the GaAs region between the corners can be better controlled by using asymmetric doping. A direct consequence of the asymmetry is that in most cases there is electron confinement only at every other corner.     

Particular nanowire superlattice as a spin filter

A nanowire superlattice of InAs and GaAs layers with In_0.47Ga_0.53As as the impure layers is proposed. The oft-neglected k³ Dresselhaus spin-orbit coupling causes the spin polarization of the electron but often can produce a limited spin polarization. In this nanowire superlattice, Dresselhaus term produce complete spin filtering by optimizing the distance between the In_0.47Ga_0.53As layers and the Indium (In) in the impure layers. The proposed structure is an optimized nanowire superlattice that can efficiently filter any component of electron spins according to its energy. In fact, this nanowire superlattice is an energy dependent spin filter structure.     

Dependence of electronic properties on nitrogen concentration in GaAs1−xNx dilute alloys

Based on the pseudopotential scheme, the effect of nitrogen concentration on electronic properties of zinc-blende GaAs_1−xN_x alloys has been investigated for small amounts of N. The agreement between our calculated electronic band parameters and the available experimental data is generally reasonable. In agreement with recent experiment, we find that the incorporation of a few percent of N in the material of interest reduces substantially the fundamental band-gap energy and narrows the full valence band width. The electron and heavy hole effective masses are found to decrease rapidly when adding a concentration of nitrogen less than 0.005 in GaAs. This may increase the mobility of electrons and heavy holes providing new opportunities regarding the transport properties. The information derived from the present study shows that GaAs_1−xN_x (0?x?0.05) properties may have an important optoelectronic applications in infrared and mid-infrared spectral regions.     

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.     

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.     

Point defects and amplification in active layers of InGaAs/AlGaAs heterostructures

The energy levels of gallium and arsenic vacancies as well as silicon impurities in the band gap of In _x Ga_{1 ? x} As have been found as functions of the indium content. The effect of defects on the lasing output power and on the optimal reflection coefficient of output mirrors of laser diode arrays (LDAs) based on the In_0.11Ga_0.89As/AlGaAs heterostructures has been estimated. It has been shown that the lasing output power of LDAs whose active level contains defects with deep energy levels in the band gap is substantially lower (with other conditions being the same) than that of LDAs with shallow level defects in their active layers.     

Emission and elastic strain in InAs dot-in-a well InGaAs/GaAs structures

The paper presents the photoluminescence (PL) study of InAs quantum dots (QDs) embedded in the asymmetric GaAs/In_xGa_1?xAs/In_0.15Ga_0.85As/GaAs quantum wells (QWs) with the different compositions of capping In_xGa_1?xAs layers. The composition of the buffer In_0.15Ga_0.85As layer was the same in all studied QD structures, but the In content (parameter x) in the capping In_xGa_1?xAs layers varied within the range 0.10–0.25. The In concentration (x) increase in the In_xGa_1?xAs capping layers is accompanied by the variation non-monotonously of InAs QD emission: PL intensity and peak positions. To understand the reasons of PL variation, the PL temperature dependences and X ray diffraction (XRD) have been investigated. It was revealed that the level of elastic deformation (elastic strain) and the Ga/In interdiffusion at the In_xGa_1?xAs/InAs QD interface are characterized by the non-monotonous dependences versus parameter x. The physical reasons for the non-monotonous variation of the elastic strains and PL parameters in studied QD structures have been discussed.     

Design of strain compensated InGaAs/GaAsSb type-II quantum well structures for mid-infrared photodiodes

In this paper, the transition wavelength and wave function overlap of type-II In_xGa_1-xAs/GaAs_1-ySb_y quantum wells are numerically calculated using a 4-band k · p Hamiltonian model. The simulation results indicate that absorption wavelength from 2 to 4?μm can be achieved with a strain compensated quantum well structure. The transition wavelength and wave function overlap can be optimized by properly selecting the thicknesses and composition of the quantum well layers.