Hafnium Silicate dielectrics fabricated by RF magnetron sputtering.

International audienceStructural and composition properties of hafnium silicate layers fabricated by RF magnetron sputtering were studied by means of spectroscopic ellipsometry, X-ray diffraction, transmission electron microscopy and attenuated total reflection infrared spectroscopy with respect to the deposition parameters and postdeposition annealing treatment. The variation of the deposition conditions allows the temperature of amorphous-crystalline phase transformation of pure hafnium oxide layers to be controlled. It is shown that the silicon incorporation in oxide matrix prevents the formation of interfacial silicon oxide layer and plays a major role in the stability of the structure of hafnium based layers remaining an amorphous state upon annealing at 900-950 °C

Controlled Synthesis of β-SiC Nanopowders with Variable Stoichiometry Using Inductively Coupled Plasma

In the growing field of nanomaterials, SiC nanoparticles arouse interest for numerous applications. The inductively coupled plasma (ICP) technique allows obtaining large amount of SiC nanopowders from cheap coarse SiC powders. In this paper, the effects on the SiC structure of the process pressure, the plasma gas composition, and the precursor nature are addressed. The powders were characterized by X-ray diffraction (XRD), Raman and fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and high resolution electron microscopy (HREM), chemical analyses, BET and photon correlation spectroscopy (PCS) measurements. Whatever the precursor (α- or β-SiC), the nanoparticles were crystallised in the cubic β-SiC phase, with average sizes in the 20-40nm range. Few residual grains of precursor were observed, and the decarburization due to the reductive Ar-H2 plasma lead to the appearance of Si nanograins. The stoichiometry of the final product was found to be controllable by the process pressure and the addition of methan

On the relevance of large scale pulsed-laser deposition: Evidence of structural heterogeneities in ZnO thin films

Pulsed-laser deposition is known as a well-suited method for growing thin films of oxide compounds presenting a wide range of functional properties. A limitation of this method for industrial process is the very anisotropic expansion dynamics of the plasma plume, which induces difficulties to grow on large scale films with homogeneous thickness and composition. The specific aspect of the crystalline or orientation uniformity has not been investigated, despite its important role on oxide films properties. In this work, the crystalline parameters and the texture of zinc oxide films are studied as a function of position with respect to the central axis of the plasma plume. We demonstrate the existence of large non-uniformities in the films. The stoichiometry, the lattice parameter, and the distribution of crystallites orientations drastically depend on the position with respect to the plume axis, i.e., on the oblique incidence of the ablated species. The origin of these non-uniformities, in particular, the unexpected tilted orientation of the ZnO c-axis may be attributed to the combined effects of the oblique incidence and of the ratio between oxygen and zinc fluxes reaching the surface of the growing film

Atomic scale observation of phase separation and formation of silicon clusters in Hf higk-κ silicates

International audienceHafnium silicate films were fabricated by RF reactive magnetron sputtering technique. Fine microstructural analyses of the films were performed by means of high-resolution transmission electron microscopy and atom probe tomography. A thermal treatment of as-grown homogeneous films leads to a phase separation process. The formation of SiO2 and HfO2 phases as well as pure Si one was revealed. This latter was found to be amorphous Si nanoclusters, distributed uniformly in the film volume. Their mean diameter and density were estimated to be about 2.8 nm and (2.960.4) 1017 Si-ncs/cm3, respectively. The mechanism of the decomposition process was proposed. The obtained results pave the way for future microelectronic and photonic applications of Hf-based high-j dielectrics with embedded Si nanocluster

The synthesis of TiO2 thin film by Chemical Bath Deposition (CBD) method

Titanium oxide (TiO2) films have several advantages for applications in solar cells and very commonly used as a photo-catalyst for degradation of environmental pollutants. In this study, TiO2 films were synthesized using, a simple, less expensive, low temperature and convenient for large area deposition method, a chemical bath deposition (CBD) and their structural and optical properties were examined at various calcinations temperatures. The X-ray diffraction (XRD) technique shows the presence of the picks characteristic of anatase phase after annealing our films at 500°C, 600°C and rutile phase appears after heat treatment at 700°C. The surface morphology of the deposited films was characterized by the FEG scanning electronic microscopy (FEGSEM) and atomic force microscopy (AFM). Energy dispersive X-ray spectroscopy (EDS) analysis was used to determine the chemical composition of the prepared films. The UV-Vis-NIR spectroscopy shows that the film exhibits a transmission around 60%. The indirect band gap of the deposited films was between 2.88 and 3.22 eV

NUMERICAL SIMULATION OF PHOTOCURRENT IN A SOLAR CELL BASED AMORPHOUS SILICON

We propose in this work, a method of simulation based on the resolution of the equations of continuities for homostructures of silicon-based solar, and used a method of calculation the photocurrent delivered by the silicon solar cell applying the equations of continuities and the currents by analogy to the phenomena of loads transport according to the model of an homojunction n-a-Si:H/p-a-Si:H. We used Matlab software to simulate and optimize the layers thicknesses to achieve the maximum photocurrent generated under AM1.5 solar spectrum. The optimization of donor layer thickness shows clearly that the best results are obtained with the finest structures.  We worked out a numerical model based on the resolution of the equations of continuities who gave the results in good agreement with literature and which allowed, moreover a better control of the performances of the cells based on silicon, for their improvement

Study of Cu/In/Se/Se thin films prepared by the Stacked Elemental Layer (SEL) technique

CuInSe2 thin films have been grown on Corning glass and Si (100) substrates using stacked elemental layers (SEL) processing. The influence of substrate’s nature and substrate’s temperature were studied. X-ray diffraction and SEM measurements have shown that the films exhibit an excellent crystallinity and crystallize in a tetragonal structure. Scanning electron microscopy investigations have shown that the films consist in a structure with large grains in the range 80 – 200 nm. Increasing the deposition temperature from room temperature to 300 °C has lead to a change in the composition and morphology of the films. Characteristic peaks of the chalcopyrite structure such as (101), (211) and (311) were clearly observed for both layers upon annealing at 450°C as evidenced by X-ray diffraction study. The determined lattice parameters were a = 0.57725 (6) nm, b = 1.1621 (2) nm for sample prepared at room temperature and a = 0.57770 (4) nm, b = 1.1602 (1) nm for Ts = 300°C. The crystallographic structure of the CuInSe2 sample was analyzed by Rietveld analysis using X-ray powder diffraction data. UV-Vis-NIR Spectrophotometry was used to investigate the optical characteristics of different Cu/In/Se/Se thin layers in the spectral range between 300 – 2000 nm. The optical band-gap of our materials increases from 0.98 to 1.01 eV

Resistive switching and charge transport mechanisms in ITO/ZnO/p-Si devices

[EN] The resistive switching properties of ITO/ZnO/p-Si devices have been studied, which present well-defined resistance states with more than five orders of magnitude difference in current. Both the high resistance state (HRS) and the low resistance state (LRS) were induced by either sweeping or pulsing the voltage, observing some differences in the HRS. Finally, the charge transport mechanisms dominating the pristine, HRS, and LRS states have been analyzed in depth, and the obtained structural parameters suggest a partial re-oxidation of the conductive nanofilaments and a reduction of the effective conductive area.This work was financially supported by the Spanish Ministry of Economy and Competitiveness (Project Nos. TEC2012-38540-C02-01 and TEC2016-76849-C2-1-R). O.B. also acknowledges the subprogram "Ayudas para Contratos Predoctorales para la Formacion de Doctores" of the Spanish Ministry of Economy and Competitiveness for economical support. X.P., C.L., and C.G. are grateful to C. Frilay for his expertise in the maintenance of the sputtering kit used for the growth of the ZnO films.Blázquez, O.; Frieiro, J.; López-Vidrier, J.; Guillaume, C.; Portier, X.; Labbé, C.; Sanchis Kilders, P.... (2018). Resistive switching and charge transport mechanisms in ITO/ZnO/p-Si devices. Applied Physics Letters. 113(18):1-6. https://doi.org/10.1063/1.50469111611318I. G. Baek , M. S. Lee , S. Sco , M. J. Lee , D. H. Seo , D.S. Suh , J. C. Park , S. O. Park , H. S. Kim , I. K. Yoo , U.I. Chung , and J. T. Moon , in IEDM Technical Digest. IEEE International Electron Devices Meeting, 2004 ( IEEE, 2004), pp. 587–590.Waser, R., & Aono, M. (2007). Nanoionics-based resistive switching memories. Nature Materials, 6(11), 833-840. doi:10.1038/nmat2023Kaeriyama, S., Sakamoto, T., Sunamura, H., Mizuno, M., Kawaura, H., Hasegawa, T., … Aono, M. (2005). A nonvolatile programmable solid-electrolyte nanometer switch. IEEE Journal of Solid-State Circuits, 40(1), 168-176. doi:10.1109/jssc.2004.837244Strukov, D. B., & Likharev, K. K. (2005). CMOL FPGA: a reconfigurable architecture for hybrid digital circuits with two-terminal nanodevices. Nanotechnology, 16(6), 888-900. doi:10.1088/0957-4484/16/6/045Mehonic, A., Cueff, S., Wojdak, M., Hudziak, S., Jambois, O., Labbé, C., … Kenyon, A. J. (2012). Resistive switching in silicon suboxide films. Journal of Applied Physics, 111(7), 074507. doi:10.1063/1.3701581Mehonic, A., Vrajitoarea, A., Cueff, S., Hudziak, S., Howe, H., Labbé, C., … Kenyon, A. J. (2013). Quantum Conductance in Silicon Oxide Resistive Memory Devices. Scientific Reports, 3(1). doi:10.1038/srep02708Pickett, M. D., Medeiros-Ribeiro, G., & Williams, R. S. (2012). A scalable neuristor built with Mott memristors. Nature Materials, 12(2), 114-117. doi:10.1038/nmat3510Jo, S. H., Chang, T., Ebong, I., Bhadviya, B. B., Mazumder, P., & Lu, W. (2010). Nanoscale Memristor Device as Synapse in Neuromorphic Systems. Nano Letters, 10(4), 1297-1301. doi:10.1021/nl904092hVescio, G., Crespo-Yepes, A., Alonso, D., Claramunt, S., Porti, M., Rodriguez, R., … Aymerich, X. (2017). Inkjet Printed HfO2-Based ReRAMs: First Demonstration and Performance Characterization. IEEE Electron Device Letters, 38(4), 457-460. doi:10.1109/led.2017.2668599Valov, I. (2013). Redox-Based Resistive Switching Memories (ReRAMs): Electrochemical Systems at the Atomic Scale. ChemElectroChem, 1(1), 26-36. doi:10.1002/celc.201300165Martín, G., González, M. B., Campabadal, F., Peiró, F., Cornet, A., & Estradé, S. (2017). Transmission electron microscopy assessment of conductive-filament formation in Ni–HfO2–Si resistive-switching operational devices. Applied Physics Express, 11(1), 014101. doi:10.7567/apex.11.014101Simanjuntak, F. M., Panda, D., Wei, K.-H., & Tseng, T.-Y. (2016). Status and Prospects of ZnO-Based Resistive Switching Memory Devices. Nanoscale Research Letters, 11(1). doi:10.1186/s11671-016-1570-yKim, J., & Yong, K. (2011). Mechanism Study of ZnO Nanorod-Bundle Sensors for H2S Gas Sensing. The Journal of Physical Chemistry C, 115(15), 7218-7224. doi:10.1021/jp110129fYuan, Q., Zhao, Y.-P., Li, L., & Wang, T. (2009). Ab Initio Study of ZnO-Based Gas-Sensing Mechanisms: Surface Reconstruction and Charge Transfer. The Journal of Physical Chemistry C, 113(15), 6107-6113. doi:10.1021/jp810161jSeo, J. W., Park, J.-W., Lim, K. S., Yang, J.-H., & Kang, S. J. (2008). Transparent resistive random access memory and its characteristics for nonvolatile resistive switching. Applied Physics Letters, 93(22), 223505. doi:10.1063/1.3041643Rahaman, S. Z., Maikap, S., Chiu, H.-C., Lin, C.-H., Wu, T.-Y., Chen, Y.-S., … Tsai, M.-J. (2010). Bipolar Resistive Switching Memory Using Cu Metallic Filament in Ge[sub 0.4]Se[sub 0.6] Solid Electrolyte. Electrochemical and Solid-State Letters, 13(5), H159. doi:10.1149/1.3339449Simanjuntak, F. M., Panda, D., Tsai, T.-L., Lin, C.-A., Wei, K.-H., & Tseng, T.-Y. (2015). Enhancing the memory window of AZO/ZnO/ITO transparent resistive switching devices by modulating the oxygen vacancy concentration of the top electrode. Journal of Materials Science, 50(21), 6961-6969. doi:10.1007/s10853-015-9247-ySimanjuntak, F. M., Prasad, O. K., Panda, D., Lin, C.-A., Tsai, T.-L., Wei, K.-H., & Tseng, T.-Y. (2016). Impacts of Co doping on ZnO transparent switching memory device characteristics. Applied Physics Letters, 108(18), 183506. doi:10.1063/1.4948598Simanjuntak, F. M., Panda, D., Tsai, T.-L., Lin, C.-A., Wei, K.-H., & Tseng, T.-Y. (2015). Enhanced switching uniformity in AZO/ZnO1−x/ITO transparent resistive memory devices by bipolar double forming. Applied Physics Letters, 107(3), 033505. doi:10.1063/1.4927284Liu, Q., Guan, W., Long, S., Jia, R., Liu, M., & Chen, J. (2008). Resistive switching memory effect of ZrO[sub 2] films with Zr[sup +] implanted. Applied Physics Letters, 92(1), 012117. doi:10.1063/1.2832660Shuai, Y., Zhou, S., Bürger, D., Helm, M., & Schmidt, H. (2011). Nonvolatile bipolar resistive switching in Au/BiFeO3/Pt. Journal of Applied Physics, 109(12), 124117. doi:10.1063/1.3601113Chen, J.-Y., Hsin, C.-L., Huang, C.-W., Chiu, C.-H., Huang, Y.-T., Lin, S.-J., … Chen, L.-J. (2013). Dynamic Evolution of Conducting Nanofilament in Resistive Switching Memories. Nano Letters, 13(8), 3671-3677. doi:10.1021/nl4015638Hubbard, W. A., Kerelsky, A., Jasmin, G., White, E. R., Lodico, J., Mecklenburg, M., & Regan, B. C. (2015). Nanofilament Formation and Regeneration During Cu/Al2O3 Resistive Memory Switching. Nano Letters, 15(6), 3983-3987. doi:10.1021/acs.nanolett.5b00901Liu, Q., Sun, J., Lv, H., Long, S., Yin, K., Wan, N., … Liu, M. (2012). Real-Time Observation on Dynamic Growth/Dissolution of Conductive Filaments in Oxide-Electrolyte-Based ReRAM. Advanced Materials, 24(14), 1844-1849. doi:10.1002/adma.201104104Zhu, X., Wu, H.-Z., Qiu, D.-J., Yuan, Z., Jin, G., Kong, J., & Shen, W. (2010). Photoluminescence and resonant Raman scattering in N-doped ZnO thin films. Optics Communications, 283(13), 2695-2699. doi:10.1016/j.optcom.2010.03.006Cerqueira, M. F., Vasilevskiy, M. I., Oliveira, F., Rolo, A. G., Viseu, T., Ayres de Campos, J., … Correia, R. (2011). Resonant Raman scattering in ZnO:Mn and ZnO:Mn:Al thin films grown by RF sputtering. Journal of Physics: Condensed Matter, 23(33), 334205. doi:10.1088/0953-8984/23/33/334205Marchewka, A., Roesgen, B., Skaja, K., Du, H., Jia, C.-L., Mayer, J., … Menzel, S. (2015). Nanoionic Resistive Switching Memories: On the Physical Nature of the Dynamic Reset Process. Advanced Electronic Materials, 2(1), 1500233. doi:10.1002/aelm.201500233Krzywiecki, M., Grządziel, L., Sarfraz, A., Iqbal, D., Szwajca, A., & Erbe, A. (2015). Zinc oxide as a defect-dominated material in thin films for photovoltaic applications – experimental determination of defect levels, quantification of composition, and construction of band diagram. Physical Chemistry Chemical Physics, 17(15), 10004-10013. doi:10.1039/c5cp00112aMurgatroyd, P. N. (1970). Theory of space-charge-limited current enhanced by Frenkel effect. Journal of Physics D: Applied Physics, 3(2), 151-156. doi:10.1088/0022-3727/3/2/308Electron emission in intense electric fields. (1928). Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character, 119(781), 173-181. doi:10.1098/rspa.1928.0091Özgür, Ü., Alivov, Y. I., Liu, C., Teke, A., Reshchikov, M. A., Doğan, S., … Morkoç, H. (2005). A comprehensive review of ZnO materials and devices. Journal of Applied Physics, 98(4), 041301. doi:10.1063/1.1992666Kaidashev, E. M., Lorenz, M., von Wenckstern, H., Rahm, A., Semmelhack, H.-C., Han, K.-H., … Grundmann, M. (2003). High electron mobility of epitaxial ZnO thin films on c-plane sapphire grown by multistep pulsed-laser deposition. Applied Physics Letters, 82(22), 3901-3903. doi:10.1063/1.1578694Gall, D. (2016). Electron mean free path in elemental metals. Journal of Applied Physics, 119(8), 085101. doi:10.1063/1.4942216Lee, W., Park, J., Kim, S., Woo, J., Shin, J., Choi, G., … Hwang, H. (2012). High Current Density and Nonlinearity Combination of Selection Device Based on TaOx/TiO2/TaOx Structure for One Selector–One Resistor Arrays. ACS Nano, 6(9), 8166-8172. doi:10.1021/nn3028776Kwon, D.-H., Kim, K. M., Jang, J. H., Jeon, J. M., Lee, M. H., Kim, G. H., … Hwang, C. S. (2010). Atomic structure of conducting nanofilaments in TiO2 resistive switching memory. Nature Nanotechnology, 5(2), 148-153. doi:10.1038/nnano.2009.456Choi, B. J., Torrezan, A. C., Strachan, J. P., Kotula, P. G., Lohn, A. J., Marinella, M. J., … Yang, J. J. (2016). High‐Speed and Low‐Energy Nitride Memristors. Advanced Functional Materials, 26(29), 5290-5296. doi:10.1002/adfm.201600680Sun, X. (2006). Designing efficient field emission into ZnO. SPIE Newsroom. doi:10.1117/2.1200602.0101Hu, C., Wang, Q., Bai, S., Xu, M., He, D., Lyu, D., & Qi, J. (2017). The effect of oxygen vacancy on switching mechanism of ZnO resistive switching memory. Applied Physics Letters, 110(7), 073501. doi:10.1063/1.4976512Gul, F., & Efeoglu, H. (2017). Bipolar resistive switching and conduction mechanism of an Al/ZnO/Al-based memristor. Superlattices and Microstructures, 101, 172-179. doi:10.1016/j.spmi.2016.11.043Blázquez, O., Martín, G., Camps, I., Mariscal, A., López-Vidrier, J., Ramírez, J. M., … Garrido, B. (2018). Memristive behaviour of Si-Al oxynitride thin films: the role of oxygen and nitrogen vacancies in the electroforming process. Nanotechnology, 29(23), 235702. doi:10.1088/1361-6528/aab744Bersuker, G., Gilmer, D. C., Veksler, D., Kirsch, P., Vandelli, L., Padovani, A., … Nafría, M. (2011). Metal oxide resistive memory switching mechanism based on conductive filament properties. Journal of Applied Physics, 110(12), 124518. doi:10.1063/1.367156

Light-activated electroforming in ITO/ZnO/p-Si resistive switching devices

We report on light-activated electroforming of ZnO/p-Si heterojunction memristors with transparent indium tin oxide as the top electrode. Light-generated electron-hole pairs in the p-type substrate are separated by the external electric field and electrons are injected into the active ZnO layer. The additional application of voltage pulses allows achieving different resistance states that end up in the realization of the low resistance state (LRS). This process requires much less voltage compared to dark conditions, thus avoiding undesired current overshoots and achieving a self-compliant device. The transport mechanisms governing each resistance state are studied and discussed. An evolution from an electrode-limited to a space charge-limited transport is observed along the electroforming process before reaching the LRS, which is ascribed to the progressive formation of conductive paths that consequently induce the growth of conductive nanofilaments through the ZnO layer. This work was financially supported by the Spanish Ministry of Economy and Competitiveness (Project Nos. TEC2012-38540-C02-01 and TEC2016-76849-C2-1-R). O.B. also acknowledges the subprogram "Ayudas para Contratos Predoctorales para la Formación de-Doctores" from the Spanish Ministry of Economy and Competitiveness for economical support. J.L.F. acknowledges the subprogram "Ayudas para la Formación de Profesorado Universitario" (No. FPU16/06257) from the Spanish Ministry of Education, Culture and Sports for economical support. X.P., C.L., and C.G. are grateful to C. Frilay for his expertise in the maintenance of the sputtering setup used for the growth of the ZnO films