Changes in the electrical transport of ZnO under visible light

Complex impedance spectroscopy data in the frequency range 16Hz < f < 3 MHz at room temperature were acquired on pure ZnO single crystal and thin film. The measured impedance of the ZnO samples shows large changes with time after exposure to or covering them from visible light. At fixed times Cole-Cole-diagrams indicate the presence of a single relaxation process. A simple analysis of the impedance data allows us to obtain two main relaxation times. The behavior for both, ZnO crystal and thin film, is similar but the thin film shows shorter relaxation times. The analysis indicates the existence of two different photo-active defects with activation energies between ~0.8 eV and ~1.1 eV.Comment: 11 pages, 9 figures. Solid state communications, in pres

Influence of the band bending on the photoconductivity of Li-doped ZnO microwires

Combining photoconductivity and photoluminescence measurements we have studied the band bending behavior with the Li-doping content in ZnO microwires. Our results reveal the presence of in-gap acceptor levels with energies ranging from 100 meV to 600 meV above valence band maximum. We have found that the band bending plays an important role in the photoconductivity modifying the life time of the photocarriers and enhancing the near band edge peak of photoluminescence in Li-doped samples. Using a simple model we have evaluated the influence of the band-bending on the relaxation time for the photoconductivity.Fil: Ferreyra, Jorge Mario. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; ArgentinaFil: Bridoux, German. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; ArgentinaFil: Villafuerte, Manuel Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; ArgentinaFil: Straube, Benjamin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; ArgentinaFil: Zamora, J.. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; ArgentinaFil: Figueroa, C. A.. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; ArgentinaFil: Heluani, S.P.. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; Argentin

Defect Spectroscopy Of Single Zno Microwires

The point defects of single ZnO microwires grown by carbothermal reduction were studied by microphotoluminescence, photoresistance excitation spectra, and resistance as a function of the temperature. We found the deep level defect density profile along the microwire showing that the concentration of defects decreases from the base to the tip of the microwires and this effect correlates with a band gap narrowing. The results show a characteristic deep defect levels inside the gap at 0.88 eV from the top of the VB. The resistance as a function of the temperature shows defect levels next to the bottom of the CB at 110 meV and a mean defect concentration of 4 × 1018 cm-3. This combination of techniques allows us to study the band gap values and defects states inside the gap in single ZnO microwires and opens the possibility to be used as a defect spectroscopy method. © 2014 AIP Publishing LLC.11513Look, D.C., Hemsky, J.W., Sizelove, J., (1999) Phys. Rev. Lett, 82, p. 2552. , 10.1103/PhysRevLett.82.2552Xu, X.L., Lau, S.P., Chen, J.S., Chen, G.Y., Tay, B.K., (2001) J. Cryst. Growth, 223, p. 201. , 10.1016/S0022-0248(01)00611-XCarrasco, J., Lopez, N., Illas, F., (2004) Phys. Rev. Lett., 93, p. 225502. , 10.1103/PhysRevLett.93.225502Morkoc, H., Ozgur, U., (2009) Zinc Oxide, Fundamentals, Materials, and Device Technology, , 1st ed. (Wiley-VCH Verlag GmbH & Co. KGaA, Federal Republic of Germany)Der Walle, C.G.V., (2000) Phys. Rev. Lett., 85, p. 1012. , 10.1103/PhysRevLett.85.1012Wong, K.M., Alay-E-Abbas, S.M., Fang, Y., Shaukat, A., Lei, Y., (2013) J. Appl. Phys., 114, p. 034901. , 10.1063/1.4813517Brenner, S.S., (1956) J. Appl. Phys., 27, p. 1484. , 10.1063/1.1722294Shalish, I., Temkin, H., Narayanamurti, V., (2004) Phys. Rev. B, 69, p. 245401. , 10.1103/PhysRevB.69.245401Leiter, F., Alves, H., Hofstaetter, A., Hofmann, D., Meyer, B., (2001) Phys. Status Solidi B, 226, pp. R4. , 10.1002/1521-3951(200107)226:13.0.CO;2-FVanheusden, K., Warren, W.L., Seager, C.H., Tallant, D.R., Voigt, J.A., Gnade, B.E., (1996) J. Appl. Phys., 79, p. 7983. , 10.1063/1.362349Kohan, A.F., Ceder, G., Morgan, D., Van De Walle, C.G., (2000) Phys. Rev. B, 61, p. 15019. , 10.1103/PhysRevB.61.15019Janotti, A., Van De Walle, C.G., (2007) Phys. Rev. B, 76, p. 165202. , 10.1103/PhysRevB.76.165202Lin, B., Fu, Z., Jia, Y., (2001) Appl. Phys. Lett., 79, p. 943. , 10.1063/1.1394173Liu, M., Kitai, A., Mascher, P., (1992) J. Lumin., 54, p. 35. , 10.1016/0022-2313(92)90047-DVidya, R., Ravindran, P., Fjellvåg, H., Svensson, B.G., Monakhov, E., Ganchenkova, M., Nieminen, R.M., (2011) Phys. Rev. B, 83, p. 045206. , 10.1103/PhysRevB.83.045206Dingle, R., (1969) Phys. Rev. Lett., 23, p. 579. , 10.1103/PhysRevLett.23.579Alivov, Y., Chukichev, M., Nikitenko, V., (2004) J. Semicond., 38, p. 31. , 10.1134/1.1641129Simmons, J.G., Foreman, J.V., Liu, J., Everitt, H.O., (2013) Appl. Phys. Lett., 103, p. 201110. , 10.1063/1.4829745Cao, B.Q., Lorenz, M., Brandt, M., Von Wenckstern, H., Lenzner, J., Biehne, G., Grundmann, M., (2008) Phys. Status Solidi RRL, 2, p. 37. , 10.1002/pssr.200701268Qin, W., Nagase, T., Umakoshi, Y., Szpunar, J.A., (2007) J. Phys.: Condens. Matter, 19, p. 236217. , 10.1088/0953-8984/19/23/236217Dietrich, C.P., Lange, M., Klpfel, F.J., Von Wenckstern, H., Schmidt-Grund, R., Grundmann, M., (2011) Appl. Phys. Lett., 98, p. 031105. , 10.1063/1.3544939Wang, J., Wang, Z., Huang, B., Ma, Y., Liu, Y., Qin, X., Zhang, X., Dai, Y., (2012) ACS Appl. Mater. Interfaces, 4, p. 4024. , 10.1021/am300835pMott, N., Davis, E., (1979) Electronic Processes in Non-Crystalline Materials, , 2nd ed. (University Press, Oxford)Shklovskii, B., Efros, A., (1984) Electronic Properties of Doped Semiconductors, , Solid-State Science Vol. 45 (Springer-Verlag)Schmidt-Mende, L., Macmanus-Driscoll, J., (2007) Mater. Today, 10, p. 40. , 10.1016/S1369-7021(07)70078-0Börseth, T.M., Svensson, B.G., Kuznetsov, A.Y., Klason, P., Zhao, Q.X., Willander, M., (2006) Appl. Phys. Lett., 89, p. 262112. , 10.1063/1.2424641Tuomisto, F., Ranki, V., Saarinen, K., (2003) Phys. Rev. Lett., 91, p. 205502. , 10.1103/PhysRevLett.91.20550