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In this work, we have characterized by transmission electron microscopy techniques the structural properties of InAlAsSb/InGaAs/InP heterostructures, with target applications in high efficiency solar cells. Previous photoluminescence (PL) 1 analysis suggested the existence of compositional fluctuations in the active layer of these heterostructures. 220 bright field (BF) 2 diffraction contrast micrographs have revealed strong strain contrast in the InGaAs buffer layer, related to the existence of these compositional fluctuations. The effect of a decomposed buffer on the growth of the InAlAsSb layer has been analyzed through the simulation of the strain fields in the heterostructure using the finite elements method (FEM). 3 These simulations have shown that the strain in the buffer layer due to the compositional fluctuations only affects the first few nm of the InAlAsSb layer. The analysis by aberration corrected high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) 4 and electron energy loss spectroscopy (EELS) 5 of the composition of the InAlAsSb layer reveals that any compositional fluctuation is only observed as an average effect, rather than in the form of clustering or atomically sharp transitions. The limitations of these techniques for the detection of small 3D compositional fluctuations are discussed.

The effect of a post-growth thermal treatment in two different heterostructures with InAlAsSb as the top layer grown by molecular beam epitaxy lattice-matched to InP, have been studied by diffraction contrast transmission electron microscopy (TEM). 1 This novel top cell layer material with application in ultra-high efficiency solar cells were grown on (001) InP substrate with or without an InGaAs buffer layer. Initial photoluminescence (PL) 2 measurements revealed deviations from their predicted bandgap, suggesting non-random atomic distribution of the quaternary layer. Then, a thermal annealing was performed at different temperatures and times. The effect on the structure of the InAlAsSb active layer caused by the new arrangement of layers and the post-growth annealing treatments has been reported. Our results show that the small compositional fluctuations of the as-grown heterostructures disappear after being annealed, and the bandgap energy correspondingly increases towards the predicted value.

5 páginas, 3 fiugras, 1 tabla.-- PACS: 81.70.Jb; 61.16.Bg, A phenomenological method is developed to determine the composition of materials, with atomic column resolution, by analysis of integrated intensities of aberration-corrected Z-contrast scanning transmission electron microscopy images. The method is exemplified for InAsxP1−x alloys using epitaxial thin films with calibrated compositions as standards. Using this approach we have determined the composition of the two-dimensional wetting layer formed between self-assembled InAs quantum wires on InP(0 0 1) substrates., This work was supported by the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, US DOE (MVandSJP),the SANDiE European Network of Excellence (Contract No NMP4-CT-2004-500101),the Spanish MEC (TEC2005-05781-C03-01y02,NAN2004-09109-C04-01,Consoli- der-Ingenio2010CSD2006-00019),the CAM(S0505ESP0200) and the Junta de Andalucia(PAI research groups TEP-120 and TIC- 145;project No PAI05-TEP-00383).

The influence of post-growth annealing on the microstructure and photoluminescence (PL) of GaAsBi alloys grown on (3 1 1)B GaAs is analyzed. Conventional transmission electron microscopy (TEM) performed on as-grown samples evidence the presence of structural defects and a mosaic structure in the GaAsBi layer. A sequence of stacking faults at regions close to the GaAs/GaAsBi interface are observed in high resolution TEM images. After annealing at 473 K during 3 h the mosaic structure disappears, the presence of defects is reduced and the PL peak intensely enhances. © 2010 Elsevier B.V. All rights reserved.

3 páginas, 3 figuras.-- Progress in Applied Surface, Interface and Thin Film Science - SURFINT SREN II.-- PACS codes: 68.37.Lp; 81.05.Ea; 81.15.Hi, The compositional distribution of InAs quantum dots grown by molecular beam epitaxy on GaAs capped InAs quantum dots has been studied in this work. Upper quantum dots are nucleated preferentially on top of the quantum dots underneath, which have been nucleated by droplet epitaxy. The growth process of these nanostructures, which are usually called as quantum dots molecules, has been explained. In order to understand this growth process, the analysis of the strain has been carried out from a 3D model of the nanostructure built from transmission electron microscopy images sensitive to the composition., This work was supported by the Spanish MCI (TEC2008-06756-C03-02/TEC), CONSOLIDER CSD2009-00013, and the Junta de Andalucia (PAI research groups TEP-120 and TIC-145, project P08-TEP-03516).

In this work, photomodulated transmittance (PT) has been applied to investigate the energy gap of GaBiAs layers grown on (001) and (311)B GaAs substrates. In PT spectra, a clear resonance has been observed below the GaAs edge. This resonance has been attributed to the energy gap-related absorption in GaBiAs. The energy and broadening of PT resonances have been determined using a standard approach in electromodulation spectroscopy. It has been found that the crystallographic orientation of GaAs substrate influences on the incorporation of Bi atoms into GaAs and quality of GaBiAs layers. The Bi-related energy gap reduction has been determined to be ~90meV per percent of Bi. In addition to PT spectra, common transmittance spectra have been measured and the energy gap of GaBiAs has been determined from the square of the absorption coefficient α2 around the band-gap edge. It has been found that the tail of density of states is significant for GaBiAs and influences the accuracy of energy gap determination from the α2 plot. In the case of PT spectra, the energy gap is determined unambiguously since this technique is directly sensitive to singularities in the density of states.

Erratum to: ‘‘Column-by-column compositional mapping by Z-contrast imaging’’ [Ultramicroscopy 109(2) (2009) 172–176] S.I. Molina a, , D.L. Sales , P.L. Galindo , D. Fuster , Y. Gonz alez , B. Al en , L. Gonz alez , M. Varela , S.J. Pennycook d a Departamento de Ciencia de los Materiales e I.M. y Q.I., Facultad de Ciencias, Universidad de C adiz, Campus Ŕio San Pedro, s/n, 11510 Puerto Real, C adiz, Spain b Departamento de Lenguajes y Sistemas Inform aticos, CASEM, Universidad de C adiz, Campus Ŕio San Pedro, s/n, 11510 Puerto Real, C adiz, Spain c Instituto de Microelectronica de Madrid (CNM, CSIC), Isaac Newton 8, 28760 Tres Cantos, Madrid, Spain d Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA