Indium segregation and reevaporation effects on the photoluminescence properties of highly strained InxGa1−xAs/GaAs quantum wells (original) (raw)
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Physical review. B, Condensed matter, 1988
Structure has been observed in the photoluminescence and photoconductivity spectra of In"Ga& "As/GaAs (x &1) strained quantum wells grown by molecular-beam epitaxy onto GaAs(001)-oriented substrates. Features in the spectra at energies larger than the energy gap of In"oa& "As are interpreted as the allowed excitonic transitions between electron and hole subbands (including the strain-split-off valence band) in In"Gal "As. The spectra were analyzed with the conduction-band onset and the energy gap of In"Gal "As as adjustable parameters. No strain relaxation in quantum wells with thickness smaller than the critical one was observed. The strainsplit-oft' valence subband in In"Gal "As is found to be below the valence band of unstrained GaAs. The ratio of the conduction-band omset to the energy-gap discontinuity was determined to be 0.83+0.06.
Structural and optical studies of InxGa1−xAs/GaAs multiple quantum wells
Journal of Applied Physics, 1996
Strained multiple quantum wells of In x Ga 1Ϫx As/GaAs were grown by low pressure metalorganic chemical vapor deposition ͑LP-MOCVD͒ and characterized by secondary ion mass spectrometry, x-ray diffraction, and optical spectroscopy. The structural analysis demonstrates the excellent control of the interface morphology and composition achieved by MOCVD growth. Temperature dependent optical absorption, photoluminescence, and magnetotransmission were used to evaluate the well-width dependence of the major excitonic properties. The samples show sharp excitonic resonances with distinct excited states evolving into Landau-type excited states in high magnetic field. The well-width dependence of the excitonic eigenstates and of the exciton binding energy as well reproduced by envelope function and variational calculations, also in the presence of external electric field. Finally, nonlinear electro-optic modulation induced by the quantum confined Stark effect is demonstrated in a Schottky diode with extremely low switching threshold.
Exciton properties and optical response in InxGa1-xAs/GaAs strained quantum wells
Physical review. B, Condensed matter, 1994
Exciton binding energies and optical response in quantum wells and in multiple quantum wells of GaAs/In Gay As/GaAs are computed by a variational envelope-function procedure using the four-band model and the simpler two-band model. The eKect of hydrostatic and uniaxial strain are considered from a virtual-crystal stress Hamiltonian. The physical parameters used for the alloy (In Gaz As) are obtained by interpolating the parameter values of pure materials (GaAs, InAs). We verify that band-oHset values in the range of 0.30-0.45 give exciton states and optical response in good agreement with experiments. The light-hole exciton energy is also well reproduced by theory and results are very close to the continuum states of the well, its binding energy being due to the attraction of the electron, localized inside the well.
Journal of Materials Science: Materials in Electronics, 2017
characterized by non-homogeneities of QD sizes, QD compositions, QD densities and emission intensities resulting in difficulties in predicting the optical and electrical device parameters [1-8]. It was shown that the InAs QD density has been enlarged if the InAs QDs were grown on the surface of the In x Ga 1−x As buffer layer within of In x Ga 1−x As/ GaAs QWs [14]. In these structures the PL intensity was enhanced owing to the better crystal quality of surrounding QD materials [15, 16], as well as more effective the exciton capture into QWs and QDs [17-21]. Recently it was revealed that the PL intensity and PL peak positions of InAs QD emissions versus InGaAs capping layer compositions vary no monotonically [14, 16]. One of the reasons of such effect can be related to the different levels of elastic strains in In x Ga 1−x As/GaAs QWs, which depend on In x Ga 1−x As compositions. To study the strain related effects in QD structures, HR-XRD scans for the symmetrical Bragg reflection have been used. XRD and HR-XRD studies, as well as fitting the obtained HR-XRD results, permit to estimate the thickness and composition of QW layers, the level of elastic strain and its impact on InAs QD parameters in the In x Ga 1−x As/GaAs QW structures with the different In compositions in capping In x Ga 1−x As layers. 2 Experimental conditions InAs QD structures were created using the molecular beam epitaxial (MBE) growth on the (001) oriented 2′'diameter semi-insulating GaAs substrates. Each structure included a 300 nm GaAs buffer layer and a 70 nm GaAs upper final capping layer grown at 600 °C (Fig. 1). Between GaAs layers three self-organized InAs QD arrays (formed by depositing 2.4 ML of InAs at 490 °C) Abstract GaAs/In 0.15 Ga 0.85 As/In x Ga 1−x As/GaAs quantum wells (QWs) with embedded InAs quantum dots (QDs) and with variable In compositions in capping In x Ga 1−x As layers (0.10 ≤ x ≤ 0.25) have been studied by means of photoluminescence, X ray diffraction (XRD) and high resolution XRD (HR-XRD) methods. In x Ga 1−x As composition varying is accompanied by changing no monotonically the PL spectrum parameters of InAs QDs and by decreasing the InAs QD sizes. XRD and HR-XRD studies permit to control the InGaAs layer compositions and elastic strains in QWs. The analysis of HR-XRD results has shown that the level of elastic strain varies no monotonically in studied QD structures as well. The physical reasons of mentioned optical and structural effects and their dependences on capping layer compositions have been discussed.
Microelectronics Journal, 1999
Molecular Beam Epitaxy (MBE) growth of a series of Single Strained Quantum Wells (SSQWs) of InGaAs/GaAs with indium content ranging from 10% to 35% and 100 Å well thickness was performed on (001) and (111)B GaAs substrates under optimized growth conditions for simultaneous growth. The Critical Layer Thickness (CLT) of the heterostructures grown on both substrates was comparatively studied by low temperature Photoluminescence (PL). Relaxation is readily observed in the structures grown on (001) GaAs for 24% In-content. This value is in close agreement with both a calculation of the excess strain associated with the two Matthews and Blakeslee strain relieving dislocation mechanisms and the onset of three-dimensional growth. By contrast, heterostructures grown on (111)B GaAs remain pseudomorphic for In-contents above 25%. A maximum PL peak wavelength of 1.1 microns at room temperature has been reached under the growth conditions used. This would correspond to an In-content around 31%. The study shows that (111)B is a preferable choice of substrate orientation for the growth of InGaAs/GaAs heterostructures for optoelectronic applications at wavelengths beyond 1 mm.
Semiconductor Physics, Quantum Electronics and Optoelectronics
In x Ga 1-x As QW-layers embedded in GaAs matrix have been characterized by photoluminescence (PL). The relation between the PL parameters and mismatch of the lattice parameters of the layer and matrix was established. In highly strained layers several PL bands were observed instead one band. This is probably a result of alternating content of In raised only in highly strained layers.
Physical Review B, 1988
Sharp line structure associated with both the light-hole free exciton (LHFE) and heavy-hole free exciton (HHFE) in multiple-quantum-well structures of GaAs-AI"Ga& "As in photoluminescence and re6ection spectra has been deconvoluted by using photoluminescence excitation spectroscopy. A correlation is established between particular LHFE fine-structure components and specific HHFE fine-structure components. A model is developed to account for the LHFE and HHFE fine structure in these samples which exploits the nonrandom character of the observed spectra. The physical location of the excitons is demonstrated to be in regions of the well(s) with essentially identical interfacial microstructure. Evidence of difusion from effectively-narrow-well regions to wide-well regions is presented.
Le Journal de Physique Colloques
Undoped single and multiple quantum well heterostructures of InxGal-xAs-GaAs and InxGal-,As-A1 Gal-yAs are investigated by Y photoluminescence and photoconductivity spectra.The observed conduction-to-valence band offset ratio across the GaAs-strained (InGajAa intciface is AE,: AEv = 0. 8 : 0. 2 , and is iound to be reduced at the AlyGal-yAs-InxGal-xAs interface depending on the Al-and In-concentrations. The band edge offset in the (AIGa)As/GaAs system has been intensively studied for a number of years. Today several experiments1 indicate that AEcAE,, = 0.6-0.65. Recently the interest in band edge offsets has been extended to strained quantum wells (OW). The lattice mismatched (InGa)As/GaAs system is such an example. Applications of (1nGa)AslGaAs and (InGa)Asl(AIGa)As QW and superlattices extended the magnitude of the band offsets. The built-in elastic strain in these systems is due to the 7% lattice mismatch between GaAs and InAs. High quality strained single and multiple QW structures as well as superlattices can be epitaxially grown provided the thickness of the strained layers are kept small enough to avoid generation of misfit dislocation^^.^. The critical thickness LC for dislocation generation is nearly inversely proportional to the In content and being about 200A for an ln0~15Ga0.85A~ QW in GaAs. The substitution of Ga by Al is not expected to influence the critical thickness as the AIAs-GaAs lattice mismatch is only 0.1%. The conduction-to-valence band discontinuities (AEctlEv) across the interface determine the depth of the quantum wells. This ratio has been repced in a few papers4-but the obtained values are not very accurate. We have used photoluminescence (PL) and photoconduclivity (PC) to investigate undoped SOW and MOW heteros:mctures in the (1nGa)As-GaAs and (1nGa)As-(AIGa)As system. The structures were grown by molecular beam epitaxy (MBE).
Enhancement of compositional disordering in strained InxGa1-xAs/GaAs quantum wells by Zn diffusion
Superlattices and Microstructures, 1991
We report the enhancement of InGa interdiffusion in strained InxGa1- x{As}/{GaAs} (x=0.20-0.24) single quantum well (QW) structures by surface Zn diffusion. The epitaxial structures were grown by MOVPE and consist of a 1-2μm thick GaAs buffer layer, followed by the In xGa 1-xAs QW with 80-100Å thickness and a GaAs cap layer 500-1000Å thick. We have performed various shallow Zn diffusion depths for times and temperatures ranging from 1.3 to 3.5min. and 585-620°C, respectively, in order to vary the Zn concentration in the QWs. The samples were then annealed between 650-785°C under {AsH3}/{H2} to determine the enhanced InGa interdiffusion coefficient and its activation energy. A model is proposed to explain the enhancement of interdiffusion by Zn diffusion which involves an interstitial migration process.