Capacitance-transient-spectroscopy Model For Defects With Two Charge States

We formulate the set of coupled differential equations that govern the charge capture and emission process of deep levels that present two possible charge states. This solution is obtained considering the steady-state conditions imposed by DLTS (deep level transient spectroscopy) technique procedure. We distinguish three types of defects according to the predominance of one of the three different emission processes. Using our model, we reproduce DLTS spectra of doubly charged defects observed in different semiconductors such as p-type CdTe, electron and proton irradiated n-type GaAs, and sulfur-doped GaSb. Thermal barriers for carrier capture are easily introduced in our equations permitting one to reproduce experimental data even in the case of large lattice relaxation. We show that without a further analysis within the framework of our model, some DLTS spectra of defects with two states of charge might be misinterpreted as is the case for the DX center in GaSb:S.551595909597Lang, D.V., (1974) J. Appl. Phys., 45, p. 3023Harris, R.D., Newton, J.L., Watkins, G.D., (1982) Phys. Rev. Lett., 48, p. 1271Watkins, G.D., (1984) Festkörperprobleme: Advances in Solid State Physics, 24, p. 163. , edited by P. Grosse Vieweg-Verlag, BraunschweigLevinson, M., Benton, J.L., Kimerling, L.C., (1983) Phys. Rev. B, 27, p. 6216Levinson, M., Stavola, M., Benton, J.L., Kimerling, L.C., (1983) Phys. Rev. B, 28, p. 5848Levinson, M., Stavola, M., Besoni, P., Bonner, W.A., (1984) Phys. Rev. B, 30, p. 5817Zoth, G., Schröter, W., (1988) Philos. Mag., 58, p. 623Barbot, J.F., Girault, P., Blanchard, C., Hümmelgen, I.A., (1995) J. Mater. Sci., 30, p. 3471Koehler, M., Ferrari, E.F., Barbot, J.F., Hümmelgen, I.A., (1996) Phys. Rev. B, 53, p. 7805Semaltianos, N.G., Karczewsky, G., Hu, B., Wojtowicz, T., Furdyna, J.K., (1995) Phys. Rev. B, 51, p. 17499Svensson, B.G., Willander, M., (1987) J. Appl. Phys., 62, p. 2758Lalita, J., Jagadish, C., Svensson, B.G., (1995) Nucl. Instrum. Methods Phys. Res. Sect. B, 106, p. 234Pons, D., Bourgoin, J.C., (1985) J. Phys. C, 18, p. 3839Goodman, S.A., Auret, F.D., Meyer, W.E., (1990) Nucl. Instrum. Methods Phys. Res. Sect. B, 90, p. 349Ziebro, B., Hemsky, J.H., Look, D.C., (1992) J. Appl. Phys., 72, p. 78Lai, S.T., Alexiev, D., Nener, B.D., (1995) J. Appl. Phys., 78, p. 3686Dobaczewski, L., Kaczor, P., Karczewsky, G., Poole, I., (1991) Acta Phys. Pol. A, 79, p. 133Dutta, P.S., Koteswara Rao, K.S.R., Sangunni, K.S., Bhat, H.L., Kumar, V., (1994) Appl. Phys. Lett., 65, p. 1412Hubík, P., Smíd, V., Kristofik, J., Stepanek, B., Sestakova, V., (1993) Solid State Commun., 86, p. 19Poole, I., Lee, M.E., Cleverley, I.R., Peaker, A.R., Singer, K.E., (1990) Appl. Phys. Lett., 57, p. 1645Dobaczewski, L., Kaczor, P., (1991) Semicond. Sci. Technol., 6, pp. B51Lang, D.V., Logan, R.A., Jaros, M., (1979) Phys. Rev. B, 19, p. 1015Dobaczewsky, L., Kaczor, P., (1991) Semicond. Sci. Technol., 6, pp. B51(1992) Mod. Phys. Lett. B, 6, p. 15Li, M.F., Luo, Y.Y., Yu, P.Y., Weber, E.R., Fujioka, H., Du, A.Y., Chua, S.J., Lim, Y.T., (1994) Phys. Rev. B, 50, p. 7996Khachaturyan, K., Kaminska, M., Weber, E.R., Becla, P., Street, R.A., (1989) Phys. Rev. B, 40, p. 6304Schröter, W., Kronewitz, J., Gnauert, U., Riedel, F., Seibt, M., (1995) Phys. Rev. B, 52, p. 13726Pons, D., (1984) J. Appl. Phys., 55, p. 3644Barbot, J.F., Blanchard, C., Ntsoenzok, E., Vernois, J., (1996) Mat. Sci. Eng. B, 36, p. 81Tachikawa, M., Mizuta, M., Kukimoto, H., Minomura, S., (1985) Jpn. J. Appl. Phys., 24, pp. L821Maude, D.K., Portal, J.C., Mowski, I.D., Foster, T., Eaves, L., Nathan, M., Heilbum, M., Beal, R.B., (1988) Phys. Rev. Lett., 59, p. 815Theis, T.N., Mooney, P.M., Wright, S.L., (1988) Phys. Rev. Lett., 60, p. 361Chadi, D.J., Chang, K.J., (1989) Phys. Rev. B, 39, p. 10063Soares, D.A.W., Ribeiro, G.M., Sampaio, J.F., Chaves, A.S., Oliveira, A.G., (1994) Brazilian J. Phys., 24, p. 370Baj, M., Dmowski, L.H., Slupiński, T., (1993) Phys. Rev. Lett., 71, p. 352

Composites of polyvinyl alcohol and carbon (coils, undoped and nitrogen doped multiwalled carbon nanotubes) as ethanol, methanol and toluene vapor sensors

We investigate the chemical sensing behavior of composites prepared with polyvinyl alcohol and carbon materials (undoped multiwalled carbon nanotubes, nitrogen-doped multiwalled carbon nanotubes and carbon nanocoils). We determine the sensitivity of thin films of these composites for ethanol, methanol and toluene vapor, comparing their conductance and capacitance responses. The composite that exhibits highest sensitivity depends on specific vapor, vapor concentration and measured electrical response, showing that the interactivity of the carbon structure with chemical species depend on structural specificities of the carbon structure and doping. © 2011 American Scientific Publishers. All rights reserved