Epitaxial pulsed laser crystallization of amorphous germanium on GaAs

We have investigated the crystallization of amorphous germanium films on GaAs crystals using nanosecond laser pulses. The structure and composition of the crystallized layers is dominated by nonequilibrium effects induced by the fast cooling process following laser irradiation. Perfect epitaxial films are obtained for fluencies that completely melt the Ge film, but not the substrate. For higher fluencies, partial melting of the substrate leads to the formation of a (GaAs)(1-x)Ge-2x epitaxial alloy with a graded composition profile at the interface with the substrate. Since Ge and GaAs are thermodynamically immiscible in the solid phase, the formation of the alloy is attributed to the suppression of phase separation during the fast cooling process. Lower laser fluencies lead to polycrystalline layers with a patterned surface structure. The latter is attributed to the freeze-in of instabilities in the melt during the fast solidification process. (C) 2001 American Institute of Physics.9052575258

Compact Hydrogenated Amorphous Germanium Films By Ion-beam Sputtering Deposition

We explore reactive ion-beam sputtering deposition (IBSD) for the growth of a-Ge:H films. It is shown that compact a-Ge:H films can be obtained by IBSD at substrate temperatures between 180°C and 220°C by minimizing the ion bombardment of the growth surface. The infrared (IR) spectra of the best materials, as far as device applications are concerned, so-far obtained show no poly-hydride nor surface-like contributions to the Ge-H dipole vibration bands. Positron annihilation (PA) spectroscopy studies of these samples reveal smaller valence (S) parameters and larger core (W) parameters as compared with the films grown under less-favorable conditions, which indicate a relatively smaller concentration of the largest voids, the annihilation process being controlled mainly by trapping at small vacancy clusters or monovacancies. Similar IR and PA measurements on in situ ion-bombarded IBSD and RF-sputtered samples indicate that ion irradiation is a main factor in large void formation. © 2000 Elsevier Science B. V. All rights reserved.266-269 B713716Karg, F.H., Böhm, H., Pierz, K., (1989) J. Non-Cryst. Solids, 114, p. 477Turner, W.A., Jones, S.J., Pang, D., Bateman, B.E., Chen, J.H., Li, Y.M., Marques, F.C., Theye, M.L., (1990) J. Appl. Phys., 67, p. 7430Marques, F.C., Chambouleyron, I., (1989) Proceedings of the Nineth ec Solar Energy Conference, p. 1042. , W. Palz, G.T. Wrixon, P. Helm (Eds.), Kluwer, DordrechtDrüsedau, T., Schröder, B., (1994) J. Appl. Phys., 75, p. 2864Peng, Z.L., Comedi, D., Dondeo, F., Chambouleyron, I., Simpson, P.J., Mascher, P., (1999) Physica B, 274, p. 579Biersack, J.P., Haggmark, L.G., (1980) Nucl. Instrum, and Meth., 174, p. 257Yehoda, J.E., Yang, B., Vedam, K., Messier, R., (1988) J. Vac. Sci. Technol. A, 6, p. 1631Origo, F., Hammer, P., Comedi, D., Chambouleyron, I., (1998) Mater. Res. Soc. Symp. Proc., 507, p. 477Bhan, M.K., Malhotra, L.K., Kashyap, S.C., (1989) J. Appl. Phys., 65, p. 241Schultz, P.J., Lynn, K.G., (1988) Rev. Mod. Phys., 60, p. 701Saarinen, K., Laine, T., Skog, K., Mäkinen, J., Hautojärvi, P., Rakennus, K., Uusimaa, P., Pessa, M., (1996) Phys. Rev. Lett., 77, p. 340

Sixge1-x Films And Heterojunctions Produced By Epitaxial Crystallization Of A-sixge1-x Alloys On Gaas

We studied the structural and electrical properties of crystallized a-SixGe1-x alloys with 0≤x≤1 on (100) GaAs substrates. Raman spectroscopy on laser crystallized films shows the Si-Si, Ge-Ge, and Si-Ge vibrations characteristic of crystalline SixGe 1-x alloys. The Raman polarization selection rules indicate that, while SixGe1-x films with x up to 25% are epitaxial, those with higher Si concentrations are polycrystalline with oriented grains. Heterojunctions formed by crystallizing a-Ge films on p-type GaAs exhibit Ohmic behavior. Ge/n-GaAs heterojunctions, in contrast, show rectification with current versus voltage characteristics compatible with the behavior of n-n structures. These heterojunctions are sensitive to light with wavelengths up to 1600 nm, thus demonstrating that they can be used as detectors in the spectral range for optical communications (1300-1550 nm). © 2004 Elsevier B.V. All rights reserved.338-3401 SPEC. ISS.197200Santos, P.V., Trampert, A., Dondeo, F., Comedi, D., Zhu, H.J., Ploog, K.H., Zanatta, A.R., Chambouleyron, I., (2001) J. Appl. Phys., 90, p. 2575Anderson, R.L., (1962) Solid State Electron., 5, p. 341Chang, L.L., (1965) Solid State Electron., 8, p. 721Aichmayr, G., Toet, D., Mulato, M., Santos, P.V., Spangenberg, A., Christiansen, S., Albrecht, M., Strunk, H.P., (1999) J. Appl. Phys., 85, p. 1040Cardona, M., (1982) Light Scattering in Solids II, p. 153. , M. Cardona, & G. Güntherodt. Berlin: SpringerDondeo, F., Santos, P.V., Ramsteiner, M., Comedi, D., Pudenzi, M.A.A., Chambouleyron, I., (2002) Braz. J. Phys., 32, p. 376Renucci, M.A., Renucci, J.B., Cardona, M., (1971) Light Scattering in Solids, p. 326. , M. Balkanski. Paris: FlammarionLeycuras, A., Lee, M.G., (1994) Appl. Phys. Lett., 65, p. 2296Barnett, S.A., Ray, M.A., Lastras, A., Kramer, B., Greene, J.E., Raccah, P.M., Abels, L.L., (1982) Electron. Lett., 18, p. 89

Investigation Of Ion-bombardment Effects On The Formation Of Voids During Deposition Of A-ge : H

In this work, positron annihilation (PA) and infra-red (IR) spectroscopies are combined to obtain information on the H bonding and the void size distribution as a function of deposition parameters (substrate temperature and ion-bombardment) during reactive ion-beam sputtering deposition (IBSD) for the growth of a-Ge : H films. For a-Ge : H films obtained at substrate temperatures between 180°C and 260°C without ion bombardment of the growth surface, PA studies reveal low-value valence (S) parameters and high core (W) parameters as compared with films grown under less-favorable conditions. These data indicate a relatively low concentration of large voids, the annihilation process being controlled mainly by trapping at vacancies. IR and PA measurements on IBSD samples subjected to in-situ ion-bombardment during growth indicate ion irradiation of the growth surface as a major factor responsible for large void formation. It can thus be concluded that rather compact a-Ge : H films can be obtained by IBSD at substrate temperatures between 180°C and 260°C, by minimizing the ion bombardment of the growth surface. © 1999 Elsevier Science B.V. All rights reserved.273-274579583Krause-Rehberg, R., Leipner, H.S., (1999) Positron Annihilation in Semiconductors, , Springer, BerlinAers, G.C., (1991) AIP Conference Proceeding, p. 218. , P.J. Schultz, G.R. Massoumi, P.J. Simpson (Eds.), Positron Beams for Solids and Surface, Proceedings of the Fourth International Workshop, AIP, New YorkOrigo, F., Hammer, P., Comedi, D., Chambouleyron, I., (1998) Mater. Res. Soc. Symp. Proc., 507, p. 477Drüsedau, T., Schröder, B., (1994) J. Appl. Phys., 75, p. 2864Liszkay, L., Corbel, C., Baroux, L., Hautojärvi, P., Bayhan, M., Brinkman, A.W., Tatarenko, S., (1994) Appl. Phys. Lett., 64, p. 1380Soininen, E., Mäkinen, J., Beyer, D., Hautojärvi, P., (1992) Phys. Rev. B, 46, p. 13104Schaefer, H.E., Würschum, R., (1986) Appl. Phys. A, 40, p. 14

Surface study of vitreous carbon obtained from glassy carbon powder

This work presents a surface study of monolithic vitreous (or glassy) carbon - MVC - obtained from vitreous carbon powder. Defective MVC pieces are crushed in a ball mill and size classified by sifting. The MVC powder is mixed with furfuryl-alcohol resin and compacted in a mould using a hydraulic press. Samples with different powder granulometries are produced in this way and carbonized in a furnace under nitrogen atmosphere. Complete carbonization of the powder is achieved in only one day and losses due to breakage of the pieces is less than 5%. These results compare very favorably with respect to traditional MVC production methods where full carbonization may require up to seven days and losses due to breakage can be as high as 70%. After carbonization, samples are sanded and polished. Surface roughness and microstructure are characterized by light microscopy. Porosity is quantified from micrographs using ImageJ software and nanometric height variations are measured by atomic force microscopy. © 2012 Materials Research Society