Ultrafast Time Dynamics Of The Optical Absorption Of Cdte Quantum Dots In A Glass Matrix

We study the femtosecond dynamics of the optical absorption of CdTe Quantum Dots (QDs) in glass. The samples do not show broad band photoluminescence (PL) at the infrared region (emission from deep traps). The time evolution of the absorption shows an initial decay with time constants between 1.2 to 2.2 ps. They are four to seven times greater than previously measured values in samples with prominent infrared PL band. We conclude that the presence of deep traps have a fundamental influence on the dynamics of these QDs and relate the decay times to the conditions of sample fabrication. We also find evidence that the electron stays longer than the hole in the quantum confined state (QCS) to which they were excited.274286289Gaponenko, S.V., (1996) Semic., 30, p. 315Fragnito, H.L., (1993) J. Phys., 5, pp. A179Klimov, V., (1996) Phys. Rev. B, 53, p. 1463Norris, D.J., (1994) Phys. Rev. Lett., 72, p. 2612Liu, Y., (1995) J. Mat. Sci. Lett., 14, p. 635Liu, Y., (1996) J. Mat. Sci. Lett., 15, p. 892Medeiros Neto, J.A., (1991) Appl. Phys. Lett., 59, p. 2715De Oliveira, C.R.M., (1996) Appl. Phys. Lett., 66, p. 439Hache, F., (1991) JOSA B, 8, p. 1802Tomita, M., (1989) JOSA B, 6, p. 165Liu, L.C., Risbud, S.H., (1990) J. Appl. Phys., 68, p. 28Arellano, W.A., (1996), MSc. dissertation, UNICAMPRios, J.M.M., PhD thesis, UNICAMP (199)Misawa, K., (1991) Chem. Phys. Lett., 183, p. 113Hoffman, D.K., (1992) Phys. Rev. B, 45, p. 6247Meyer, B.K., (1992) Phys. Rev. B, 46, p. 15135Biernacki, S., (1993) Phys. Rev. B, 48, p. 11726Emanuelsson, P., (1993) Phys. Rev. B, 47, p. 15578Meyer, B.K., Hofmann, D.M., (1995) Appl. Phys. A, 61, p. 213Richard, T., (1996) Phys. Rev. B, 53, p. 7287Nirmal, M., (1995) Phys. Rev. Lett., 75, p. 3728Chamarro, M., (1996) Phys. Rev. B, 53, p. 1336Lewandowski, A.C., (1990) J. Appl. Phys., 68, p. 2196Khattack, G.M., Scott, C.G., (1991) J. Phys. Condensed Matter, 3, p. 8619Davis, C.B., (1993) Phys. Rev. B, 47, p. 13363Szatkowski, J., (1994) J. Phys. Cond. Matt., 6, p. 7935Marotti, R.E., (1996) Braz. J. of Phys., 26, p. 19

Intraband Ultrafast Relaxation In Cdte Quantum Dots Dispersed In A Glass Matrix

We present a study of the relaxation process between the discrete carrier levels of CdTe quantum dots, and its influence on the optical absorption spectrum. The evolution of the state populations is modeled by means of the rate equations for the system. Including homogeneous and inhomogeneous broadenings, we calculate the dynamic spectral hole-burning when some quantum dots are excited to states other than those involved in the lowest lying discrete transition. We compare it with experimental data of time-resolved differential transmission spectroscopy in a femtosecond scale, obtained through the pump and probe method. The samples were CdTe quantum dots doped glasses. Alterations of the absorption in all the probe spectrum (∼ 200 meV) are seen. During the first moments after the excitation reaches the sample, a shift to the infrared in the bleaching is also observed. We believe this is due to a relaxation process described here.261193197Wu, W.Y., Schulman, J.N., Hsu, T.Y., Efron, U., (1987) Appl. Phys. Lett., 51 (10), p. 710Medeiros Neto, J.A., Barbosa, L.C., Cesar, C.L., Alves, O.L., Galembeck, F., (1991) Appl. Phys. Lett., 59 (21), p. 2715De Paula, A.M., Private CommunicationDe Oliveira, C.R.M., De Paula, A.M., Plentz Filho, F.O., Medeiros Neto, J.A., Barbosa, L.C., Alves, O.L., Menezes, E.A., Cesar, C.L., (1995) Appl. Phys. Lett., 66 (4), p. 439Sercel, P.C., Vahala, K.J., (1990) Phys. Rev. B, 42 (6), p. 3690Peyghambarian, N., Fluegel, B., Hulin, D., Migus, A., Joffre, M., Antonetti, A., Koch, S.W., Linberg, M., (1989) IEEE J. Quantum Electron., QE-25 (12), p. 2516R. E. Marotti, S. Tsuda and C. H. Brito Cruz, XVIII ENFMC, Caxambu, 1995Éfros, Al.L., Kharchenko, V.A., Rosen, M., (1995) Solid State Comm., 93 (4), p. 281Puls, J., Jungnickel, V., Henneberger, F., Schlsgen, A., (1994) J. Cryst. Growth, 138, p. 100

Optical, electrical and structural characterization of chloridedoped ZnO nanopillars obtained by electrodeposition

As-grown and chloride-doped ZnO nanopillars were electrodeposited onto bareFTO/glass and ZnO-compact layer/FTO/glass substrates. To analyse the effect of the presence of chloride ions in the electrolytic bath, NH4Cl was progressively added up to 0.02 mol L-1. As preliminary examination, the morphology of ZnO nanostructures was analysed by SEM micrographs and chlorine incorporation was detected by EDS. Then, a detailed analysis comprising structural, electrical, optical and defect properties was constructed using XRD, electrical resistance measurements and UV-Vis-IR spectroscopy. As the chlorine concentration in the film increases, XRD reveals a displacement of diffracted planes due to macrostrain of the ZnO lattice and the electrical resistance diminishes. Also, the UV optical absorption edge shifts to higher energies due to Moss-Burstein effect which corresponds to electron densities in the order of 1 to 6 x 1019 cm-3, and the infrared spectra reveal the presence of free electrons, allowing a moreprecise determination of the free electron densities.Fil: Berruet, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Gau, D. L. Universidad de la Republica. Facultad de Ingeniería. Departamento de Física; UruguayFil: Dalchiele, E.A. Universidad de la Republica. Facultad de Ingeniería. Departamento de Física; UruguayFil: Vazquez, Marcela Vivian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Marotti, R.E. Universidad de la Republica. Facultad de Ingeniería. Departamento de Física; Urugua

Cu2ZnSnS4 thin films prepared by sulfurization of co-electrodeposited metallic precursors

Cu2ZnSnS4 (CZTS) thin films were prepared by thermal sulfurization of co-electrodeposited CuZnSn (CZT) metal precursors. Electrodeposition times between 10 and 40 min were used to study the influence of this parameter on the composition, structure, thickness, and morphology of the sulfurized films. CZT precursors and CZTS films were characterized by X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), and Raman spectroscopy. The morphologies were evaluated by electronic microscopy. The electrodeposition time was found to influence the chemical composition of the metal precursor, especially the Cu and Sn content. Furthermore, XRD results showed the formation of Cu5Zn8, while Sn seemed to be present in an amorphous state. A cauliflower-like morphology was observed in the precursors, especially at long deposition times, which can be related to an electrodeposition mechanism controlled by mass transfer. A significant increase of the film thickness was observed after sulfurization. The morphology changed to round particles and presented a bi-layered structure with an internal compact layer of nanometer size particles and an external layer formed by micrometer-size particles. Raman spectroscopy, XRD, and EDS measurements confirmed the formation of crystalline CZTS after sulfurization. In addition, a disperse Cu2S secondary phase co-existed in the film. Increasing the precursor deposition time increased the amount of secondary phases in the film after sulfurization. Direct energy gap values close to 1.5 eV were estimated for CZTS films using transmittance spectra in the infrared region. CZTS films obtained with short electrodeposition times are promising as absorbers in kesterite thin films solar cells.Fil: Valdes, Matias Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Di Iorio, Yesica Dolores. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Castañeda, K.. Universidad del Quindio; ColombiaFil: Marotti, R.E.. Universidad de la República; UruguayFil: Vazquez, Marcela Vivian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin

Optical and structural properties of nanostructured ZnO thin films deposited onto FTO/glass substrate by a solution-based technique

Nanostructured zinc oxide thin films were spin coated on conductive glass substrates via a sol-gel based technique using zinc acetate dihydrate as precursor. The pH of the alkalis used as catalytic agents in the hydrolysis step is shown to have a strong effect on the structural and morphological properties of the deposited ZnO. The size of the particles was observed by Transmission Electron Microscopy (TEM), while Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) and Atomic Force Microscopy (AFM), were used to analyze the morphology of the films. X-ray iffraction (XRD) and Raman spectra provided evidence of crystal growth together with an increase in the crystalline degree of the hexagonal wurtzite structure after annealing. The bandgap energy was estimated by Tauc´s method and found to decrease after annealing, which is attributed to an increase in the crystallite size and to the presence of less defect sites. A good correlation between crystallite size and absorption edges was found. The photoluminescence spectra of as-deposited samples depend on the nature and pH values of catalytic agent used, and reveal the presence of a broad visible emission attributed to a variety of intrinsic defects.Fil: Berruet, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina;Fil: Pereyra, C.J.. Universidad de la República. Facultad de Ingenieria. Instituto de Física. Centro Interdisciplinario de Nanotecnología, Química y Física de Materiales; Uruguay;Fil: Mhlongo, G.H.. Council for Scientific and Industrial Research. National Centre for Nano-Structured Materials; Sudafrica;Fil: Dhlamini, M.S.. Council for Scientific and Industrial Research. National Centre for Nano-Structured Materials; Sudafrica; University of South Africa. Department of Physics; Sudafrica;Fil: Hillie, K.T.. Council for Scientific and Industrial Research. National Centre for Nano-Structured Materials; Sudafrica; University of the Free State. Department of Physics; Sudafrica;Fil: Vazquez, Marcela Vivian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina;Fil: Marotti, R.E.. Universidad de la Republica. Facultad de Ingenieria. Instituto de Fisica y CINQUIFIMA; Uruguay

Efficiency improvements in solution-based CuInS 2 solar cells incorporating a Cl-doped ZnO nanopillars array

Solar cells are prepared combining ZnO as n-type window In2S3 as buffer layer and CuInS2 as p-type absorbing layer. Superstrate configuration is chosen so that all the materials could be prepared using inexpensive and eco-friendly techniques, based on solution processed deposition methods and non-toxic materials, avoiding vacuum high temperature Cd-containing layers and KCN purification stages. Also, no further sulfurization treatment is involved in the preparation. To improve the collection efficiency, the cells are built using two different ZnO nanostructures (with and without Cl-doping) and compared to the response of a cell prepared with just one dense ZnO layer. The photoresponse of the three different solar cells is analysed by J–V curves under illumination and intensity-modulated photovoltage/photocurrent spectroscopy. A systematic characterization of the morphology and composition is carried out using X-ray diffraction Raman confocal and electronic microscopy. The introduction of a nanostructured layer is not enough to produce a marked improvement in any of the electrical parameters. Instead, the presence of Cl-doped nanopillars is shown to increase the efficiency of the solar cells up to a maximum value of 2.8%. A better series resistance together with a higher value for the charge collection efficiency contributes to explain the corresponding improvement in cell efficiency.Fil: Di Iorio, Yesica Dolores. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Berruet, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Gau, D. L.. Universidad de la República; UruguayFil: Spera, E. L.. Universidad de la República; UruguayFil: Pereyra, C. J.. Universidad de la República; UruguayFil: Marotti, R.E.. Universidad de la República; UruguayFil: Vazquez, Marcela Vivian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin

Cdte Quantum Dots By Melt Heat Treatment In Borosilicate Glasses

CdTe quantum dots in borosilicate glasses were produced and their growth kinetics, the effects of quantum confinement for electrons and phonons and the time resolved optical transmission were studied. Quantum dots in the range of 10 to 25 Å with a 5% size dispersion were grown. The growth kinetics were studied by small angle X-ray scattering using synchrotron light. A spherical k · p model for the electron confinement explains absorption data and selection rules, and a dielectric continuum model for the phonon confinement could explain the resonant longitudinal and surface optical phonons, as well as their overtone combinations. The time response of absorption was studied by a pump-probe measurement on the femtosecond time scale. For samples showing a large amount of surface traps the recovery time can be as fast as 300 fs, while for an almost surface trap free sample it remains on the 1-3 ps time scale. © 1997 Elsevier Science B.V.219205211Efros, A.L., Efros, A.L., (1982) Sov. Phys. Semicond., 16, p. 772Ekimov, A.I., Onushchenko, A.A., (1982) Sov. Phys. Semicond., 16, p. 775Warnock, J., Awschalom, D.D., (1985) Phys. Rev., B32, p. 5529Potter, B.G., Simmons, J.H., (1988) Phys. Rev., B37, p. 10838Borrelli, N.F., Hall, D.W., Holland, H.J., Smith, D.W., (1987) J. Appl. Phys., 61, p. 5399Banyai, L., Hu, Y.Z., Lindberg, M., Koch, S.W., (1988) Phys. Rev., B38, p. 8142Peyghambarian, N., Fluegel, B., Hulin, D., Migus, A., Joffre, M., Antonetti, A., Koch, S.W., Lindberg, M., (1989) IEEE J. Quant. Elect., 25, p. 2516Alivisatos, A.P., Colvin, V.L., Goldstein, A.N., Olshavsky, M.A., Shiang, J.J., (1990) Physical Phenomena in Granular Materials, p. 870. , ed. T.H. Geballe, G.C. Cody and P. Sheng Materials Research Society, Pittsburg, PARighini, G.C., (1996) Proc. SPIE, Optics for Science and New Technology, 2778Mackenzie, J.D., Ulrich, D.R., (1990) SPIE Proc. Sol-Gel Optics, 1328, p. 2Nasu, H., Tsunetomo, K., Tokumitsu, Y., Osaka, Y., (1989) Jap. J. Appl. Phys., 25, pp. L862Ekimov, A.I., Onushchenko, A.A., (1982) Sov. Phys. Semicond., 16, p. 775Neto, J.A.M., Barbosa, L.C., Alves, O.L., Garrido, F.M.S., (1991) Proc. 2nd Int. Ceram. Sci. Tech., Ceram. Trans., 20, p. 161Reynoso, V.C.S., De Paula, A.M., Cuevas, R.F., Medeiros Neto, J.A., Alves, O.L., Cesar, C.L., Barbosa, L.C., (1995) Electr. Lett., 31, p. 1013Tsunetomo, K., Ohtsuka, S., Koyama, T., Tanaka, S., Sasaki, F., Kobayashi, S., (1995) Nonlinear Opt., 13, p. 109Medeiros Neto, J.A., Barbosa, L.C., Cesar, C.L., Alves, O.L., Galembeck, F., (1991) Appl. Phys. Lett., 59, p. 2715Esch, V., Fluegel, B., Khitrova, G., Gibbs, H.M., Jiang, Xu., Kang, K., Koch, S.W., Peyghanbarian, N., (1990) Phys. Rev., B42, p. 7450Liu, Y., Reynoso, V.C.S., Barbosa, L.C., Brito Cruz, C.H., Cesar, C.L., Fragnito, H.L., Alves, O.L., (1996) J. Mater. Sci. Lett., 15, p. 142Craievich, A.F., Alves, O.L., Barbosa, L.C., (1993) J. Phys. (Paris) Colloq., C8, p. 373Craievich, A.F., Alves, O.L., Barbosa, L.C., (1995) Rev. Sci. Instrum., 66, p. 1338Reynoso, V.C.S., Liu, Y., Rojas, R.F.C., Aranha, N., Cesar, C.L., Barbosa, L.C., Alves, O.L., (1996) J. Mater. Sci. Lett., 15, p. 1037Liu, Y., Reynoso, V.C.S., Barbosa, L.C., Rojas, R.F.C., Fragnito, H.L., Cesar, C.L., Alves, O.L., (1995) J. Mater. Sci. Lett., 14, p. 635Liu, Y., Reynoso, V.C.S., Rojas, R.F.C., Brito Cruz, C.H., Cesar, C.L., Fragnito, H.L., Alves, O.L., Barbosa, L.C., (1996) J. Mater. Sci. Lett., 15, p. 892De Paula, A.M., Barbosa, L.C., Brito Cruz, C.H., Alves, O.L., Sajurjo, J.A., Cesar, C.L., (1996) Appl. Phys. Lett., 69, p. 357De Oliveira, C.R.M., De Paula, A.M., Plentz Filho, F.O., Medeiros Neto, J.A., Barbosa, L.C., Alves, O.L., Menezes, E.A., Cesar, C.L., (1995) Appl. Phys. Lett., 66, p. 439Fragnito, H.L., Rios, J.M.M., Duarte, A.S., Palange, E., Medeiros Neto, J.A., Cesar, C.L., Barbosa, L.C., Brito Cruz, C.H., (1993) J. Phys.: Condensed Mater., 5, pp. A179Paul, A., (1982) Chemistry of Glasses, p. 148. , Chapman and Hall, LondonDuffy, J.A., Ingram, M.D., (1976) J. Non-Cryst. Solids, 21, p. 373Yükselici, H., Persan, P.D., Hayes, T.M., (1995) Phys. Rev., B52, p. 11763Landau, L.D., Lifshitz, E.M., (1993) Physical Kinetics, p. 427. , Pergamon, OxfordTurnbull, D., (1956) Solid State Physics, p. 225. , ed. F. Seitz and D. Turnbull Academic Press, New YorkKoch, S.W., (1984) Lectures Notes in Physics, 207, p. 18. , Springer, BerlinChristian, J.W., (1981) The Theory of Transformations in Metals and Alloys, 2nd Ed., (PART I), p. 418. , Pergamon, OxfordBanyai, L., Koch, S.W., (1993) Semiconductor Quantum Dots, Series on Atomic, Molecular and Optical Physics, 2. , World Scientific, SingaporeLiu, L.C., Risbud, S.H., (1990) J. Appl. Phys., 68, p. 28Lifshitz, I.M., Slyozov, V.V., (1959) Sov. Phys. JETP, 35, p. 331Lifshitz, I.M., Slyozov, V.V., (1961) J. Phys. Chem. Solids, 19, p. 3