Strain relaxation in InGaAs/GaAs quantum wells grown on GaAs (111)A substrates (original) (raw)
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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.
Microelectronics Journal, 1999
A series of InGaAs/GaAs Single Strained Quantum Wells (SSQWs) with indium content ranging from 25% to 35% and 100 Å well thickness were grown on two different (111)B GaAs off-axis substrates under optimized growth conditions for simultaneous growth. Optoelectronic properties were studied in terms of low temperature photoluminescence (PL). Results indicate a PL emission dependence with the substrate used, this dependence being stronger for highly strained systems. In order to determine the source of this dependence, samples were studied by Planar View Transmission Electron Microscopy (PVTEM). Relaxation mechanisms seem to act in a different way regarding the misoriented substrate used. Although previous theoretical results have already reported this dependence, this is the first direct evidence of this phenomenon for SSQWs. The results of these two different techniques will be compared and discussed.
Optical studies of strain effects in quantum wells grown on (311) and (100) GaAs substrates
Physical Review B, 2001
Pseudomorphic InGaAs/GaAs quantum wells ͑QW's͒ grown on vicinal substrates show a blueshift of the photoluminescence ͑PL͒ emissions with respect to ͑100͒ ͑nominal͒ ones. This effect has been discussed in the literature and it is associated with an inhomogeneous distribution of stresses in narrow quantum wells. In order to study the shift of the PL emissions at large substrate misorientation angles, we have made PL measurements on three InGaAs/GaAs QW's (30 Å wide͒, grown on (311)A, (311)B, and ͑100͒ substrates. We have done theoretical calculations considering the effect of strain on the conduction and valence bands of the QW's, where a single fitting parameter accounts for the inhomogeneous distribution of strain. Our model agrees with previously obtained results and reproduces the experimental PL blueshifts observed for the studied samples, showing that in relatively wider quantum wells the inhomogeneous distribution of strain and indium segregation play a less important role than in narrow ones. In ͑100͒ and (311)A GaAs/AlGaAs samples subjected to an external hydrostatic pressure, our model shows, for both samples, that the blueshift of the QW PL emissions increases with pressure, in good agreement with experimental results, emphasizing the strong relation between strain and blueshift regardless of the growth direction.
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).
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.
Optical study of strained and relaxed epitaxial InxGa1−xAs on GaAs
Journal of Applied Physics, 1995
Photoreflectance (PR) at different temperatures and spectroellipsometry (SE) at room temperature were used to study, in a systematic and complementary way, the optical response of a series of strained and relaxed In,Ga, -,As (x<O.15) epilayers. All the samples were grown by molecular-beam epitaxy on GaAs, both with and without a GaAs cap layer, which in the thinnest samples determines a single-quantum-well configuration. The effects of the strain on the optical structures En, El, and E,+A., observed in the 1.2-3.3 eV photon-energy range were analyzed by fitting standard critical points (CP) line shapes to the PR and SE spectra. The CP experimental energies versus x were compared with the relations obtained in the framework of the elastic strain theory and, in the quantum-well structures, of the envelope-function scheme. The excellent agreement between experiment and theory allowed us to determine, independently and only by optical techniques, the strain E and the composition x values, which compare well with those measured by x-ray diffraction. Additional information concerning the critical thickness for the pseudomorphic growth and the residual strain in quasirelaxed layers was achieved. 0 1995 American Institute of Physics.
HigHighly strained InGaAs/GaAs quantum wells emitting beyond 1.2 µm
Crystal Research and Technology, 2005
Highly strained In x Ga 1-x As quantum wells (QWs) with GaAs barriers emitting around 1.2 µm are grown on GaAs substrates by metal organic vapour phase epitaxy (MOVPE) at low growth temperatures using conventional precursors. The effects of growth temperature, V/III ratio and growth rate on QW composition and luminescence properties are studied. The variation of indium incorporation with V/III ratio at a growth temperature of 510°C is found to be opposite to the results reported for 700°C. By an appropriate choice of the growth parameters, we could extend the room temperature photoluminescence (PL) wavelength of InGaAs/GaAs QWs up to about 1.24 µm which corresponds to an average indium content of 41% in the QW. The results of the growth study were applied to broad area laser diodes emitting at 1193 nm with low threshold current densities.
Thermal Stability of Strained InGaAs/GaAs Single Quantum Wells
MRS Proceedings, 1989
We present a study of the structural stability of InGaAs/GaAs strained single quantum wells (SQW) grown with a variety of indium compositions and with well widths close to critical thickness values. The samples were grown by molecular beam epitaxy and were subjected to furnace annealing as well as ion implantation followed by rapid thermal annealing. Changes in low temperature photoluminescence linewidths were used to evaluate the stability of strained SQWs. We observed both strain relief, in wide SQWs and strain recovery, in higher indium composition narrow quantum wells which were partially relaxed (low dislocation density) as-grown.
New relaxation mechanisms in InGaAs/GaAs (111) multiple quantum well
Microelectronics Journal, 1999
A study by planar view transmission electron microscopy (PVTEM) of crystalline defect types in InGaAs/GaAs MQW grown on GaAs(111)B substrates is presented. The In-content of In x Ga 1Ϫx As layers was increased from x 0.1 to 0.3. The relaxation in structures with low In-content (x Ͻ 0.2) occurred mainly through the formation of a triangular network of misfit dislocations (MDs) along each one of the three ͗1