Emitting heterostructures with a bilayer InGaAs/GaAsSb/GaAs quantum well and a GaMnAs ferromagnetic layer

The radiative and magnetic properties of novel heterostructures with a bilayer InGaAs/GaAsSb/GaAs quantum well and a GaMnAs ferromagnetic layer are studied. The circular polarization of electroluminescent radiation is observed at temperatures from 10 to 160 K. The magnetic field dependences of the degree of circular polarization are nonlinear with a hysteresis loop at temperatures from 10 to 50 K, and they become linear at higher temperatures. The magnitude of polarization at the saturation magnetization of GaMnAs in the 2000 Oe field remains at the level of ~0.2%.     

High-strain InGaAs/GaAs quantum well grown by MOCVD

High-strain InGaAs/GaAs quantum wells （QWs） are grown by low-pressure metal-organic chemical vapor deposition （LP-MOCVD）. Photoluminescence （PL） at room temperature is applied for evaluation of the optical property. The influence of growth temperature, V/III ratio, and growth rate on PL characteristic are investigated. It is found that the growth temperature and V/III ratio have strong effects on the peak wavelength and PL intensity. The full-width at half-maximum （FWHM） of PL peak increases with higher growth rate of InGaAs layer. The FWHM of the PL peak located at 1039 nm is 20.1 meV, which grows at 600 ℃ with V/ III ratio of 42.7 and growth rate of 0.96 μm/h.     

Isolation spectra for InGaAs/GaAs strained single quantum well laser diode optical switches

The spectral dependence of gain and loss for an InGaAs/GaAs strained single quantum well laser diode were measured. High gain and high isolation at the second quantized transition wavelength can be obtained with a low injection current. A strained single quantum well structure is suitable for construction of an integrated optical matrix switch with low power consumption.     

Photoluminescence studies of GaAs/GaAlAs multiple quantum well heterostructures

The photoluminescence excited by He:Ne and Nd:YAG lasers of GaAs/Ga_0.75Al_0.25As multiple quantum well heterostructures grown by MBE was measured as a function of temperature from 4.2 K up to room temperature and for different pumping powers at constant temperature. The excitonic transitions associated with carriers confined in the quantum wells as well as other transitions associated with impurities either already present in the substrates or introduced into the samples during growth are identified in the spectra and fully characterized. From Arrhenius plots of the photoluminescence peak integrated intensities versus inverse temperature, activation energies are estimated for acceptor defects in the samples as well as for quantum well related excitonic transitions. Photoluminescence polarization experiments demonstrate a dramatic manifestation of the selection rules governing heavy hole and light hole optical transitions in quantum wells.     

Nonlocal optical properties in AlGaAs/GaAs coupled quantum well nanostructures

Nonlocal intersubband optical absorption properties in AlGaAs/GaAs coupled quantum well (CQW) nanostructures are investigated for a p-polarized light in the case of taking spatial nonlocality of optical response into account. The numerical results show that the spatial nonlocality of optical response can lead optical spectrum lines to have a radiation shift due to the nonlocal effects, and the spatial nonlocality is associated closely with the coupling effects between the potential wells of the CQW system. The dependence of the radiation shift on structure parameters of the CQW is clarified. It is also demonstrated that the maximal radiation shift and the least optical absorbance can be obtained by optimizing structure parameters of the CQW. These results may be constructive in designing nanomaterials with various nonlocality and observing the spatial nonlocal effects in experiment.     

Post-growth tailoring of the optical properties of GaAs/AlGaAs quantum well structures

In this paper we describe a method for performing post-growth bandgap engineering in the GaAs/AlGaAs quantum well system. The method used is impurity-free vacancy diffusion. Using both single and multiple quantum well data we show that this allows blue shifts in the optical properties, while retaining both their distinctive excitonic and electrical characteristics. The electrical response is modelled and no comparative degradation of the quantum confined Stark effect is predicted, and this is confirmed experimentally. Possible applications of this technique are mentioned.     

Excitation intensity dependence of lateral photocurrent in InGaAs/GaAs dot-chain structures

Optical properties of multi-layer In_xGa_1 − xAs/GaAs dot-chain heterostructures are studied by means of lateral photoconductivity (PC). Effects of carrier generation and recombination on the photoresponsivity of deep defects and quantum dot arrays are considered. It is shown that the radiative recombination significantly affects the lateral PC spectra thus leading to a nonlinear dependence of photocurrent on excitation intensity. For ground state excitation of the quantum dots the photocurrent nonlinearities are determined by a competition of both generation and recombination processes which include thermal activation.     

InGaAs/GaAs photorefractive multiple quantum well device in quantum confined Stark geometry

We have demonstrated photorefractive InGaAs/GaAs multiple-quantum-well devices in the quantum confined Stark geometry. A four-wave-mixing diffraction efficiency up to 0.3% is obtained at a wavelength of 949 nm. Proton implantation strongly reduces the maximum diffraction efficiency although it saturates the diffraction efficiency at smaller grating period comparing to as-grown device. We have also observed higher order diffractions. It is found that the space-charge field changes its pattern temporally from a sinusoidal pattern to a rectangular one with decreasing its modulation depth. Received: 7 December 2000 / Published online: 27 April 2001     

Investigation of Mn incorporation in fifteen-period InGaAs/GaAs quantum well system

A ferromagnetic ordering with a Curie temperature of 50 K of fifteen layer of InGaMnAs/GaAs multi quantum wells (MQWs) structure grown on high resistivity (100) p-type GaAs substrates by molecular beam epitaxy (MBE) was found. It is likely that the ferromagnetic exchange coupling of sample with Curie temperature of 50 K is hole-mediated resulting in Mn substituting In or Ga sites. Temperature and excitation power dependent PL emission spectra of InGaMnAs MQWs sample grown at temperature of 170 °C show that an activation energy of Mn ion on the first quantum confinement level in InGaAs quantum well is 36 meV and impurity Mn is partly ionized. It is found that the activation energy of 36 meV of Mn ion in the QW is lower than the activation energy of 110 meV for a substitutional Mn impurity in GaAs. These measurements provide strong evidence that an impurity band existing in the bandgap due to substitutional Mn ions and it is the location of the Fermi level within the impurity band that determines Curie temperature.     

Photoluminescence of InGaAs/GaAs strained-layer quantum well structures under high pressure

Abstract

Measurements of the photoluminescence (PL) of strained In_0.2Ga_0.8As/GaAs and In_0.15Ga_0.85As/GaAs quantum well structures together with the PL from bulk GaAs, in a diamond anvil cell show that the pressure coefficient of the ground confined state in the wells depends upon well width (L_Z). In the thinnest wells, the coefficient is closer to that of the bulk GaAs (10.7 meV/kbar), as expected. However, in the widest wells the coefficients tend to values (9.5meV/kbar for the 15% alloy and 9.1meV/kbar for the 20% alloy) that are significantly lower than the pressure coefficient of unstrained In_0.53Ga_0.47As (10.9meV/kbar). It is found that the low pressure coefficients can not be explained by the change in uniaxial stress with pressure due to a difference in bulk moduli between the barrier and well.     

Excitonic energy shell structure of self-assembled InGaAs/GaAs quantum dots

Performing optical spectroscopy of highly homogeneous quantum dot arrays in ultrahigh magnetic fields, an unprecedently well resolved Fock-Darwin spectrum is observed. The existence of up to four degenerate electronic shells is demonstrated where the magnetic field lifts the initial degeneracies, which reappear when levels with different angular momenta come into resonance. The resulting level shifting and crossing pattern also show evidence of many-body effects such as the mixing of configurations and exciton condensation at the resonances.     

Pressure dependence of the band-gap energy and the conduction-band mass for an n-type InGaAs/GaAs strained single-quantum well

We report the measurement of the pressure dependence for the band-gap energy and conduction-band mass for an 80 Å-wide n-type strained-single-quantum well at 4.2 K for pressures between 0 and 35 kbar and fields up to 30 T. The band-gap energy , at each pressure, was determined by extrapolating the magnetoluminescence “fan-diagram” to zero magnetic field. The pressure dependence of the band-gap energy was found to be quadratic with a linear term of about 10.3 meV/kbar and a small, , quadratic contribution. Analyses of the pressure-dependent 4.2 K magnetoluminescence data yield a conduction-band mass logarithmic pressure derivative

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Enhancement of GaAs/InGaAs quantum well emission by disordered gold nanoparticle arrays

Coupling effect of surface plasmon (SP) with InGaAs/GaAs QW emission is demonstrated experimentally. The SP resonance is generated by disordered arrays of Au nanodisks on the InGaAs/GaAs QW surface. More than twofold enhancement in QW PL is observed. Theoretical simulations also indicated that the disordered arrays of Au structures enlarged the cone angle for which light can be radiated out. The larger angle enhances the PL intensity.     

Effect of deposition period on structural and optical properties of InGaAs/GaAs quantum dots formed by InAs/GaAs short-period superlattices

Structural and optical properties of In_0.5Ga_0.5As/GaAs quantum dots (QDs) grown at 510 °C by atomic layer molecular beam epitaxy technique are studied as a function of n repeated deposition of 1-ML-thick InAs and 1-ML-thick GaAs. Cross-sectional images reveal that the QDs are formed by single large QDs rather than closely stacked InAs QDs and their shape is trapezoidal. In the image, existence of wetting layers is not clear. In 300 K-photoluminescence (PL) spectra of InGaAs QDs (n=5), 4 peaks are resolved. Origin of each peak transition is discussed. Finally, it was found that the PL linewidths of atomic layer epitaxy (ALE) QDs were weakly sensitive to cryostat temperatures (16–300 K). This is attributed to the nature of ALE QDs; higher uniformity and weaker wetting effect compared to SK QDs.     

The beam properties of high-power InGaAs/AlGaAs quantum well lasers

The vertical beam quality factor of the fundamental TE propagating mode for InGaAs/AlGaAs SCH DQW lasers emitting at 940 nm is investigated by using the transfer matrix method and the non-paraxial vectorial moment theory for non-paraxial beams. An experimental approach is given for the measurement of the equivalent vertical beam quality factor of an InGaAs/AlGaAs SCH DQW laser. It has been shown that the vertical beam quality factor M_x² is always larger than unity, whether the thickness of the active region of LDs is much smaller than the emission wavelength or not.     

Thermal,transport, and magnetotransport properties of free charge carriers in Mn-doped structures with a GaAs/InGaAs/GaAs quantum well

The results of investigation of the magnetic and transport properties of a GaAs/InGaAs/GaAs quantum well delta-doped with carbon and manganese from different sides and containing a ferromagnetic phase are analyzed. A thermodynamic model is formulated and the composition of a system consisting of neutral Mn atoms, Mn ions, and holes in the quantum well is calculated for determining the concentration of free charge carriers. The contributions to the resistance from different mechanisms of hole scattering are calculated, and good agreement with the experimental temperature dependences of the resistance is attained. The calculated and experimental values of the negative magnetoresistance associated with variation in the contribution of scattering from magnetic ions of the spin-polarized system of charge carriers are found to be in quantitative agreement.     

Simulation of the indium profile in InGaAs/GaAs quantum-size heterostructures

A new approach to describe phenomena attendant on the growth of thin InGaAs epitaxial layers by hydride MOCVD in terms of which the boundary gas layer is considered as quasi-liquid is suggested. A numerical model for simulating the concentration profiles of the components in quantum-well heterostructures is developed. It is based on the assumption that a state close to thermodynamic equilibrium exists near the interface. The concentration profiles are simulated by jointly solving equations that describe heterogeneous equilibria and material balance at the interface. The indium profiles in InGaAs/GaAs quantum-size heterostructures are simulated at various parameters of the epitaxy process, such as temperature, initial component ratio in the gas phase, and boundary layer thickness. The results obtained agree well with the available experimental data.     

The photomagnetic effect in Mn delta-doped heteronanostructures with an InGaAs/GaAs quantum well

The influence of embedding a Mn delta layer into heteronunostructures with an InGaAs/GaAs quantum well on the photomagnetic spectra was investigated. The recombination parameters of a number of model structures were determined by the photomagnetic effect and planar photoconduction at high illumination.