Composition evaluation of InxGa1−xAs Stranski-Krastanow-island structures by strain state analysis

Abstract

The compositional analyses of InxGa1−x/GaAs (001) island structures grown by molecular beam epitaxy at a substrate temperature of 560 °C with nominal In contents of x=60% and 100% are presented on the basis of high resolution transmission electron microscopy micrographs. The linear dependence of the lattice parameter on the In content (Vegard’s law) is exploited to quantitatively derive composition profiles on an atomic scale by measuring local lattice parameters and displacements. The relaxation of the thin transmission electron microscopy specimen is taken into account by the accurate thickness determination using the quantitative analysis of the information from transmission electron micrographs procedure. The final evaluation step consists of finite element modeling with the appropriate sample geometry, where the In distribution is chosen to obtain the best fit between experimental and simulated displacements. The observed In content is significantly smaller than the nominal In concentration which is due to segregation of In and diffusion of Ga from the GaAs buffer into the island during the growth. The measured mean In concentration of the islands with a nominal In content of 60% (100%) is 24% (45%).

Evidence for strain in and around InAs quantum dots in GaAs from ion-channeling experiments

“…In literature, strain fields in and around the InAs QD's have been suggested. 1,8,[18][19][20] It is interesting to note that the experimentally found width of the base of the pyramids ͑ϳ10 nm͒ is able to accommodate one unit cell more of GaAs than InAs. If the strain is relieved via misfit dislocations, this would result in two GaAs half-planes per QD.…”

Effect of post-growth annealing on the optical properties of InAs/GaAs quantum dots: A tight-binding study

“…In most growth processes, nonuniform Ga incorporation in nominally InAs QDs has been reported. 2,3,4,5,6,7,8,9,10,11,12,13,14,15,16 Photoluminescence studies of annealed QDs have shown a blue-shift of their emission line, 5,6,17,18,19 which was suggested to reflect diffusion of Ga atoms from the matrix material into the QD during annealing. However, it is not clear to which extent the blue-shift is a consequence of chemical substitution (bulk GaAs has a wider band gap than InAs), and to which extent it is due to reduced strain in the QD after Ga interdiffusion, which also causes a band-gap widening.…”

Compatible composition profiles and critical sizes of alloyed quantum dots

“…5,18,19 There is much experimental evidence in support of position-dependent compositions in various QDs. 7,15,16,18 Rosenauer et al 7 evaluated the composition of In x Ga 1−x As/ GaAs QD structure by measuring local lattice parameters and displacements assuming a linear dependence of the lattice parameter on the In content ͑Vegard's law͒. Chu and Wang 20 and Duan et al 21 analyzed the strain fields for QD structures with a nonuniform composition, and showed that the strain fields are not uniform in the QD.…”

“…5 Many theoretical and experimental investigations have been conducted to understand how different growth parameters influence the size, shape, and composition of alloyed QDs, in the hope that such understanding will allow better control of their electronic properties. [5][6][7][8][9][10][11][12][13][14][15][16] A recent literature review 17 suggests that no existing theory can predict the complicated interdependence of QD shape, strain, and composition. Moreover, if a QD island grows sufficiently large, it will eventually induce strain-relieving misfit dislocations.…”