R Bartlome

Technische Universiteit Eindhoven, Eindhoven, North Brabant, Netherlands

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Publications (29)30.69 Total impact

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    ABSTRACT: Low-temperature (≤200 °C) epitaxial growth yields precise thickness, doping, and thermal-budget control, which enables advanced-design semiconductor devices. In this paper, we use plasma-enhanced chemical vapor deposition to grow homo-epitaxial layers and study the different growth modes on crystalline silicon substrates. In particular, we determine the conditions leading to epitaxial growth in light of a model that depends only on the silane concentration in the plasma and the mean free path length of surface adatoms. For such growth, we show that the presence of a persistent defective interface layer between the crystalline silicon substrate and the epitaxial layer stems not only from the growth conditions but also from unintentional contamination of the reactor. Based on our findings, we determine the plasma conditions to grow high-quality bulk epitaxial films and propose a two-step growth process to obtain device-grade material.
    Journal of Applied Physics 01/2014; 116(5):053519-053519-9. · 2.21 Impact Factor
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    ABSTRACT: Hydrogenated microcrystalline silicon (μc-Si:H) growth by very high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) is studied in an industrial-type parallel plate KAI reactor. Combined plasma and material characterization techniques allow to assess critical deposition parameters for the fabrication of high quality material. A relation between low intrinsic stress of the deposited i-layer and better performing solar cell devices is identified. Significant solar cell device improvements were achieved based on these findings: high open circuit voltages above 520 mV and fill factors above 74% were obtained for 1 μm thick μc-Si:H single junction cells and a 1.2 cm2 micromorph device with 12.3% initial (Voc=1.33 V, FF=72.4%, Jsc=12.8 mA cm−2) and above 10.0% stabilized efficiencies.
    Solar Energy Materials and Solar Cells. 01/2011;
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    ABSTRACT: Hydrogenated microcrystalline silicon (μc-Si:H) has become a material of increasing interest these last years mainly for its use in cost-effective production of tandem and triple junction thin film silicon based solar cells. Lately, the use of novel doped silicon oxide (SiOx) layers were shown to be very promising for increasing the solar cells efficiency [1,2]. We present in this study a detailed analysis on the possible reasons behind this significant increase of electrical performances. Complete solar cells were developed in an industrial type reactor with their intrinsic layer (i-layer) deposited at a high growth rate of 1 nm/s by VHF-PECVD. Different i-layer material quality and substrate roughness were systematically evaluated during this investigation. We demonstrate conversion efficiency increase of up to 29% when both these p-type and n-type doped SiOx layers are used instead of the regular microcrystalline ones, while keeping the bulk of intrinsic material unchanged and efficiencies over 8% are achieved for a wider range of plasma parameters and substrate roughness. Extensive material analysis is presented hereafter to understand the physical origins for the improvements observed. XRD, Raman and FTIR spectroscopy, intrinsic stress, FTPS and SIMS measurements were done along with SEM images of the solar cells. It is found that devices with very different efficiencies can lead to similar FTIR and FTPS spectrum. We show that the integration of doped SiOx layers reduces to some extent the influence of porous regions, i.e. microcracks, on the electrical properties of the solar cells, and the possible physical reasons for this improvement are discussed. The development of these extrinsic defects, not detected by FTPS and FTIR, is becoming especially detrimental on highly textured substrates, required for increased light trapping. This highlights the fundamental nature difference of intrinsic and extrinsic defects which can both drive the cells performances.
    Conference Record of the IEEE Photovoltaic Specialists Conference 01/2011;
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    ABSTRACT: Silicon heterojunction technology (Si-HJT) consists of thin amorphous silicon layers on monocrystalline silicon wafers and allows for photovoltaic solar cells with energy-conversion efficiencies above 20%, also at industrial-production level. This article reports how this may be achieved. First, we focus on the surface-passivation mechanism of intrinsic and doped amorphous silicon films in such solar cells, enabling record-high values for the open-circuit voltage. Next, the industrial upscaling in large-area reactors of such film deposition is discussed, including the fabrication of solar cells with energy-conversion efficiencies as high as 21%.
    Solid-State and Integrated Circuit Technology (ICSICT), 2010 10th IEEE International Conference on; 12/2010
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    M W Sigrist, R Bartlome, M Gianella
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    ABSTRACT: Laser-spectroscopic applications in medicine increase in importance. We present two medical applications of laser-based analyses of trace gases. The analysis of exhaled breath concerns the determination of the D/H isotope ratio after intake of a small amount of heavy water. The D/H isotope ratio can be used to deduce the total body water weight and lays the foundation for many other laser-based clinical applications. An elevated D/H ratio could be monitored in breath samples up to 30 days after ingestion of only 5 ml of D/sub 2/O. A second example concerns the analysis of surgical smoke produced in minimally invasive laparoscopic surgery with electroknives. The quantitative determination of harmless and hazardous compounds down to the ppm level is demonstrated. A specific example is the presence of sevoflurane at concentrations of 80 to 300 ppm, an anesthetic, which to our knowledge is measured for the first time in an abdominal cavity.
    Proc SPIE 01/2010; 7608:760808-1 - 760808-9.
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    ABSTRACT: In silicon heterojunction solar cells, thin amorphous silicon layers passivate the crystalline silicon wafer surfaces. By using in situ diagnostics during plasma-enhanced chemical vapor deposition (PECVD), the authors report how the passivation quality of such layers directly relate to the plasma conditions. Good interface passivation is obtained from highly depleted silane plasmas. Based upon this finding, layers deposited in a large-area very high frequency (40.68 MHz) PECVD reactor were optimized for heterojunction solar cells, yielding aperture efficiencies up to 20.3% on 4 cm2
    Applied Physics Letters 01/2010; · 3.52 Impact Factor
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    ABSTRACT: We review laser applications in thin-film photovoltaics (thin-film Si, CdTe, and Cu(In,Ga)Se2 solar cells). Lasers are applied in this growing field to manufacture modules, to monitor Si deposition processes, and to characterize opto-electrical properties of thin films. Unlike traditional panels based on crystalline silicon wafers, the individual cells of a thin-film photovoltaic module can be serially interconnected by laser scribing during fabrication. Laser scribing applications are described in detail, while other laserbased fabrication processes, such as laser-induced crystallization and pulsed laser deposition, are briefly reviewed. Lasers are also integrated into various diagnostic tools to analyze the composition of chemical vapors during deposition of Si thin films. Silane (SiH4), silane radicals (SiH3, SiH2, SiH, Si), and Si nanoparticles have all been monitored inside chemical vapor deposition systems. Finally, we review various thin-film characterization methods, in which lasers are implemented.
    Applied Physics B 01/2010; · 1.78 Impact Factor
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    ABSTRACT: The role of secondary gas-phase reactions during plasma-enhanced chemical vapor deposition of microcrystalline silicon is a controversial subject. In this paper, we show that the enhancement of such reactions is associated with the improvement of material properties of absorber layers deposited at high constant rate. We detect powder, a product of secondary gas-phase reactions, via infrared laser absorption spectroscopy, laser light scattering, and optical emission spectroscopy. As the powder formation is increased, we measure a systematic improvement of device performance. This demonstrates that secondary gas-phase reactions are not detrimental to the material quality of microcrystalline silicon deposited at high rate. © 2010 American Institute of Physics.
    Applied Physics Letters 01/2010; · 3.52 Impact Factor
  • R. Bartlome, B. Strahm, A. Feltrin, C. Ballif
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    ABSTRACT: We present two laser systems to monitor plasma conditions in a plasma-enhanced chemical vapor deposition chamber. The first optical system is a high-resolution quantum cascade laser-based infrared absorption spectrometer designed to measure the input silane depletion fraction (dissociation efficiency) and to determine the amorphous-to-microcrystalline silicon transition regime. The second optical system is a compact and low-cost laser light scattering device designed to detect the formation of powder particles. In the absence of such particles, the silane depletion fraction provides an in situ measurement of the film growth rate.
    Photovoltaic Specialists Conference (PVSC), 2009 34th IEEE; 07/2009
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    Richard Bartlome, Markus W Sigrist
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    ABSTRACT: Following the ingestion of only 5.1 mL of D2O, a mid-infrared laser spectrometer determines the D/H isotope ratio increase in exhaled water vapor for the first time, to the best of our knowledge. This increase is still detectable several weeks after the heavy water intake. Collected breath samples are directly transferred into a high-temperature multipass cell operated at 373 K. No breath sample preparation is required. Aside from the capability to hinder unwanted condensation, measurements at elevated temperatures offer other advantages such as a lower temperature dependence of the delta value or the possibility to vary the intensity of absorption lines. We lay the foundation for many laser-based clinical applications. As an example, we measure a total body water weight of 55.2%+/-1.8% with respect to the total body weight, in agreement with the normal value of the male population.
    Optics Letters 05/2009; 34(7):866-8. · 3.39 Impact Factor
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    R. Bartlome, M. Kaučikas, M. W. Sigrist
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    ABSTRACT: Modulated resonant photoacoustics is a sensitive technique widely used for trace gas sensing. Generally, a continuous-wave laser is modulated at a frequency corresponding to an acoustic resonance of a photoacoustic cell. Another mode of operation—which we propose to call the pulsed resonant mode—consists in matching the frequency repetition rate of a pulsed laser to an acoustic resonance of the cell. We present a theoretical model to compare the performance of these two configurations. For a given average power of the incoming light inside the cell, the pulsed resonant mode of operation (nanosecond pulses or shorter) produces π/2 times higher photoacoustic signals than the modulated resonant scheme (the latter is optimized for a 50% duty cycle). This result agrees with experiments during which both cases were investigated at 532nm using the same photoacoustic cell containing trace concentrations of NO2.
    Applied Physics B 01/2009; 96(2):561-566. · 1.78 Impact Factor
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    B. Strahm, A Feltrin, R Bartlome, C. Ballif
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    ABSTRACT: Silane and hydrogen discharges are widely used for the deposition of silicon thin film solar cells in large area plasmaenhanced chemical vapor deposition reactors. In the case of microcrystalline silicon thin film solar cells, it is of crucial importance to increase the deposition rate in order to reduce the manufacturing costs. This can be performed by using high silane concentration, and usually high RF power and high pressure, all favorable to powder formation in the discharge that generally reduces the deposition rate as well as the deposited material quality. This work presents a study of powder formation using time-resolved optical emission spectroscopy. It is shown that this technique is suitable to detect different regimes in powder formation ranging from powder free discharge to discharge producing large dust particles. Intermediate powder formation regimes include the formation of small silicon clusters at plasma ignition as well as cycle of powder growth and ejection out of the discharge, and both are observable by this low-cost and experimentally simple technique.
    Proc SPIE 01/2009;
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    ABSTRACT: Several aspects of the science and technology of thin film silicon for photovoltaic applications will be presented. The potential advantages of this technology over crystalline wafer technology will be discussed. A basic understanding of the material properties of thin film silicon layers enables to assess their potential and limitations when used in photovoltaic devices. A brief review of the production technology for thin films will be given with particular emphasis on amorphous and microcrystalline silicon. As for other photovoltaic technologies, the push for higher efficiency of thin film silicon devices is strong. An appealing feature of these materials is that they can be easily integrated in multi-junction tandem devices. For instance, stacking amorphous and microcrystalline silicon thin films in one tandem cell, the micromorph cell, increases the efficiency well above the characteristic values of single junction cells. The Institute of Microengineering (IMT) has been a pioneer in the research and development of thin film silicon photovoltaics over the last 20 years and several latest developments on are reviewed.
    01/2009;
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    R Bartlome, A Feltrin, C. Ballif
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    ABSTRACT: The silane dissociation efficiency, or depletion fraction, is an important plasma parameter by means of which the film growth rate and the amorphous-to-microcrystalline silicon transition regime can be monitored in situ. In this letter we implement a homebuilt quantum cascade laser-based absorption spectrometer to measure the silane dissociation efficiency in an industrial plasma-enhanced chemical vapor deposition system. This infrared laser-based diagnostic technique is compact, sensitive, and nonintrusive. Its resolution is good enough to resolve Doppler-broadened rotovibrational absorption lines of silane. The latter feature various absorption strengths, thereby enabling depletion measurements over a wide range of process conditions. © 2009 American Institute of Physics.
    Applied Physics Letters 01/2009; · 3.52 Impact Factor
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    Richard Bartlome, Julien M Rey, Markus W Sigrist
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    ABSTRACT: Numerous gas-sensing devices are based on infrared laser spectroscopy. In this paper, the technique is further developed and, for the first time, applied to forensic urinalysis. For this purpose, a difference frequency generation laser was coupled to an in-house-built, high-temperature multipass cell (HTMC). The continuous tuning range of the laser was extended to 329 cm(-1) in the fingerprint C-H stretching region between 3 and 4 microm. The HTMC is a long-path absorption cell designed to withstand organic samples in the vapor phase (Bartlome, R.; Baer, M.; Sigrist, M. W. Rev. Sci. Instrum. 2007, 78, 013110). Quantitative measurements were taken on pure ephedrine and pseudoephedrine vapors. Despite featuring similarities, the vapor-phase infrared spectra of these diastereoisomers are clearly distinguishable with respect to a vibrational band centered at 2970.5 and 2980.1 cm(-1), respectively. Ephedrine-positive and pseudoephedrine-positive urine samples were prepared by means of liquid-liquid extraction and directly evaporated in the HTMC without any preliminary chromatographic separation. When 10 or 20 mL of ephedrine-positive human urine is prepared, the detection limit of ephedrine, prohibited in sports as of 10 microg/mL, is 50 or 25 microg/mL, respectively. The laser spectrometer has room for much improvement; its potential is discussed with respect to doping agents detection.
    Analytical Chemistry 08/2008; 80(14):5334-41. · 5.82 Impact Factor
  • Richard Bartlome, Markus W. Sigrist
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    ABSTRACT: Following the ingestion of only 5 mL D2O, an infrared laser spectrometer determines the D/H isotope ratio increase in exhaled water vapor for the first time. No preliminary breath sample preparation is required.
    05/2008;
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    ABSTRACT: The success of laser-based trace gas sensing techniques crucially depends on the availability and performance of tunable laser sources combined with appropriate detection schemes. Besides near-infrared diode lasers, continuously tunable midinfrared quantum cascade lasers and nonlinear optical laser sources are preferentially employed today. Detection schemes are based on sensitive absorption measurements and comprise direct absorption in multi-pass cells as well as photoacoustic and cavity ringdown techniques in various configurations. We illustrate the performance of several systems implemented in our laboratory. These include time-resolved multicomponent traffic emission measurements with a mobile CO2-laser photoacoustic system, a diode-laser based cavity ringdown device for measurements of impurities in industrial process control, isotope ratio measurements with a difference frequency (DFG) laser source combined with balanced path length detection, detection of methylamines for breath analysis with both a near-IR diode laser and a DFG source, and finally, acetone measurements with a heatable multipass cell intended for vapor phase studies on doping agents in urine samples
    Applied Physics B 02/2008; 90(2). · 1.78 Impact Factor
  • R. Bartlome, M.W. Sigrist
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    ABSTRACT: Following the ingestion of only 5 mL D2O, an infrared laser spectrometer determines the D/H isotope ratio increase in exhaled water vapor for the first time. No preliminary breath sample preparation is required.
    Lasers and Electro-Optics, 2008 and 2008 Conference on Quantum Electronics and Laser Science. CLEO/QELS 2008. Conference on; 01/2008
  • R. Bartlome, M.W. Sigrist
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    ABSTRACT: Infrared spectroscopy and mass spectrometry have long been reported as the most selective analytical techniques. Sensitive laser-based detection schemes for infrared spectroscopy such as photoacoustic, cavity ring-down or multipass transmission can be found in a countless number of gas sensing devices. These methods are however not suitable for recording vapors, particularly when high temperatures are involved. This issue has brought us to design and implement a high-temperature multipass cell (HTMC). This novel type of long path absorption cell is heatable up to 723 K and has a variable optical pathlength of up to 35 m. In addition to gases, a condensed sample can be introduced into the cell and analyzed in the vapor phase. The mirrors are separately heated in order to avoid condensation on their optical surface. Furthermore, a compensation mechanism for thermal expansion has been developed to prevent fatal optical misalignments.
    Lasers and Electro-Optics, 2007 and the International Quantum Electronics Conference. CLEOE-IQEC 2007. European Conference on; 07/2007
  • R Bartlome, M Baer, M W Sigrist
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    ABSTRACT: In absorption spectroscopy, infrared spectra of heated gases or condensed samples in the vapor phase are usually recorded with a single pass heated gas cell. This device exhibits two orders of magnitude lower sensitivity than the high-temperature multipass cell presented in this article. Our device is a novel type of compact long path absorption cell that can withstand aggressive chemicals in addition to temperatures up to 723 K. The construction of the cell and its technical features are described in detail, paying special attention to the mechanisms that compensate for thermal expansion and that allow the user to vary the optical path length under any thermal or vacuum condition. The cell may be used with a laser source or implemented within a Fourier transform infrared spectrometer. Its design is compatible with optical arrangements using astigmatic mirrors or spherical mirrors in a Herriott configuration. Here we implement a homebuilt Herriott-type cell with a total optical path length of up to 35 m. In order to demonstrate the feasibility of the cell, methane and water vapor absorption lines showing dissimilar temperature effects on line intensity were recorded with the help of a mid-infrared laser source tunable between 3 and 4 microm. Emphasis is put on lines that are too weak to be recorded with a single pass cell.
    Review of Scientific Instruments 02/2007; 78(1):013110. · 1.60 Impact Factor

Publication Stats

128 Citations
30.69 Total Impact Points

Institutions

  • 2011
    • Technische Universiteit Eindhoven
      Eindhoven, North Brabant, Netherlands
  • 2009–2011
    • École Polytechnique Fédérale de Lausanne
      • Photovoltaics and Thin Film Electronics Laboratory
      Lausanne, Vaud, Switzerland
  • 2006–2009
    • ETH Zurich
      • Institute of Quantum Electronics
      Zürich, ZH, Switzerland