A. Gicquel | Université Sorbonne Paris Nord / Sorbonne Paris Nord University (original) (raw)
Papers by A. Gicquel
Diamond and Related Materials, 2007
Brillouin light scattering has been used to investigate the elastic properties of high quality ho... more Brillouin light scattering has been used to investigate the elastic properties of high quality homoepitaxial diamond layers about 1 mm thick that have been elaborated by microwave plasma assisted chemical vapour deposition. Taking advantage of the detection of different acoustic modes, a complete elastic characterization of the crystal has been achieved. Three single crystal elastic constants, namely, c 11 , (c 11 − c 12 ) / 2 and c 44 have been selectively determined, respectively, from the frequency of the longitudinal and of the shear horizontal bulk modes travelling parallel to the film surface. These determinations are in agreement with the frequency of the observed surface modes and of the bulk waves propagating at different angles from a normal single crystal film plane and consistent with the properties of natural diamond. By adding a low amount of nitrogen ranging from 2 to 50 ppm in the gas phase, the growth rates were increased from 6 to 33 μm/h whereas the mechanical properties of the resulting layers remained close to those of natural diamond.
Plasma Sources Science and Technology, 2001
We present a modelling study of pulsed H 2 /CH 4 microwave plasmas obtained under moderate pressu... more We present a modelling study of pulsed H 2 /CH 4 microwave plasmas obtained under moderate pressure discharge conditions in a tubular quartz reactor. The transport in the reactor was described using a Nusselt model for a radially quasi-homogeneous plasma. The thermal behaviour of the plasma was modelled by distinguishing a single heavy species energy mode and the electron translation mode. The chemistry was described using a 30 species-130 reaction model. The time variations of the electron energy distribution function, the species concentrations and the gas temperature were determined by solving the coupled set of the electron Boltzmann equation, species kinetics equations and a total energy equation. Some of the results obtained from the present model were compared to measurements previously carried out on the plasmas considered. Good agreement was obtained for the time variations of the gas temperature, the relative concentration of the H-atom and the intensities of the H α and the argon 750 nm emission lines. The effect of the duty cycle on the time-averaged composition and temperatures of the discharge was also studied. Results showed that moderate pressure H 2 /CH 4 pulsed discharges obtained at duty cycles of less than 20% show different behaviour than those obtained at higher duty cycles. In particular, while the plasma reaches the permanent periodic regime in less than 2 pulse-periods, i.e. 60 ms, for duty cycle values of less than 20%, long-time-scale density variations of hydrocarbon species, ions and electrons are obtained when this parameter is greater than 20%. The model was also used to determine if the use of a pulsed regime may bring some improvements in plasma-assisted diamond deposition processes. For this purpose we analysed the variation with duty cycle of the time-averaged populations of the H-atom and CH 3 that represent the key species for diamond deposition. Results showed that pulsed discharges with small duty cycle, of typically less than 20%, lead to a substantial enhancement of the time-averaged dissociation yield. On the other hand, the CH 3 concentration exhibits a strong decrease with the duty cycle. The methyl concentration in the investigated pulsed discharge is generally smaller than in continuous wave discharges obtained in the same reactor. These results indicate that short-pulse discharges would favour the formation of films with higher Raman quality, while long duty cycle pulsed discharges would enable deposition at higher growth rates.
physica status solidi (a), 2007
The use of pulsed discharges for diamond deposition has been demonstrated to ensure a better cont... more The use of pulsed discharges for diamond deposition has been demonstrated to ensure a better control of heat transfer from the plasma to the walls in microwave plasma reactors. It also favours the production of CH 3 species while keeping constant or higher the H-atom density. Higher growth rates can then be obtained. In this paper is reported an increase of the growth rate by 25% while decreasing the input microwave mean power by 15%. These results are discussed in terms of atomic hydrogen and methyl radicals densities calculated with a unstationary 1-D axial plasma model. The results show in particular that the gas temperature, which directly controls atomic hydrogen production, needs a t on of around 8ms to reach the steady state, and that 50% of atomic hydrogen is lost by recombination after a t off of 2ms.
Journal of Applied Physics, 2005
Microwave discharges of H2 admixed with CH4 in a moderate-pressure quartz bell jar reactor used f... more Microwave discharges of H2 admixed with CH4 in a moderate-pressure quartz bell jar reactor used for diamond deposition are studied numerically. Special attention was devoted to high-power densities which provide the most effective way for producing high-quality diamond films. First, a one-dimensional radial model describing the coupled phenomena of chemistry, energy transfer, as well as species and energy transport along the reactor's radial coordinate was developed. Species densities predicted with the model were compared with measurements with infrared tunable diode laser spectroscopy, resulting in validation of the model. Second, a one-dimensional axial model was used to describe the plasma flow along the reactor axis in a region between the reactor end wall and the substrate surface. This model was particularly useful for studying the plasma behavior in the vicinity of the substrate surface, where thermal and composition gradients are large. Both the radial and axial transport models are based on the same discharge model in which the plasma is described as a thermochemically nonequilibrium flow with different energy distributions for heavy species and electrons. The chemistry was described with a model containing 28 species and 131 reactions. The electron temperature, the gas temperature, and the species concentration were determined by solving a coupled set of equations. A wide range of experimental conditions used for diamond deposition was simulated, from low microwave power density (9 W cm-3, i.e., 600 W, 2500 Pa, and Tg~2200 K) to high-power density (30 W cm-3, i.e., 2 kW, 12 000 Pa, and Tg~3200 K). The main chemical paths were identified, and the major species, transport effects, and reaction pathways that govern diamond deposition plasmas are discussed.
Le Journal de Physique IV, 1991
Journal de Physique III, 1996
Diamond and Related Materials, 1998
Photoconductivity measurements on undoped diamond material can be strongly affected by the nature... more Photoconductivity measurements on undoped diamond material can be strongly affected by the nature of the electrical contacts, due to the wide band gap and high resistivity. We have used a contactless technique based on high frequency electrical measurements in order to probe the photoconductivity s HF-photo of CVD diamond films grown by a microwave assisted technique. Resonant methods, at 9.192 GHz are carried out in a microwave cavity by a reflection spectrometer. Samples are irradiated by modulated UV light. The photoconductivity s HF-photo is deduced from the variation of the quality factor and from the frequency shift. The samples studied were deposited under various growth conditions (temperature, gas mixture, etc.). The measured high frequency photoconductivity values were compared with the physical and electrical properties measured from conventional techniques (Raman spectroscopy, current-voltage and charged particle induced conductivity characterisation). The potential of this contactless high frequency measurement technique for CVD diamond characterisation is discussed.
Diamond and Related Materials, 2007
We report on electromagnetic simulations of an industrial thin film deposition process for hydrog... more We report on electromagnetic simulations of an industrial thin film deposition process for hydrogenated amorphous carbon using microwave plasmas.
Diamond and Related Materials, 1993
... regions as a function of the CH4 content of the feed gas and the deposition temperature (25 m... more ... regions as a function of the CH4 content of the feed gas and the deposition temperature (25 mbar, 600 W, 300 sccm, 4h). difference in Rz between alumina and SiC was less than 25%. The fact that diamond nucleated on the substrate when SiC was used for pretreatment of the ...
Journal of Physics: Condensed Matter, 2009
The unique properties of CVD diamond make it a compelling choice for high power electronics. In o... more The unique properties of CVD diamond make it a compelling choice for high power electronics. In order to achieve industrial use of CVD diamond, one must simultaneously obtain an excellent control of the film purity, very low defect content and a sufficiently rapid growth rate. Currently, only microwave plasma-assisted chemical vapour deposition (MPACVD) processes making use of resonant cavity systems provide enough atomic hydrogen to satisfy these requirements.
Diamond and Related Materials, 2007
Brillouin light scattering has been used to investigate the elastic properties of high quality ho... more Brillouin light scattering has been used to investigate the elastic properties of high quality homoepitaxial diamond layers about 1 mm thick that have been elaborated by microwave plasma assisted chemical vapour deposition. Taking advantage of the detection of different acoustic modes, a complete elastic characterization of the crystal has been achieved. Three single crystal elastic constants, namely, c 11 , (c 11 − c 12 ) / 2 and c 44 have been selectively determined, respectively, from the frequency of the longitudinal and of the shear horizontal bulk modes travelling parallel to the film surface. These determinations are in agreement with the frequency of the observed surface modes and of the bulk waves propagating at different angles from a normal single crystal film plane and consistent with the properties of natural diamond. By adding a low amount of nitrogen ranging from 2 to 50 ppm in the gas phase, the growth rates were increased from 6 to 33 μm/h whereas the mechanical properties of the resulting layers remained close to those of natural diamond.
Plasma Sources Science and Technology, 2001
We present a modelling study of pulsed H 2 /CH 4 microwave plasmas obtained under moderate pressu... more We present a modelling study of pulsed H 2 /CH 4 microwave plasmas obtained under moderate pressure discharge conditions in a tubular quartz reactor. The transport in the reactor was described using a Nusselt model for a radially quasi-homogeneous plasma. The thermal behaviour of the plasma was modelled by distinguishing a single heavy species energy mode and the electron translation mode. The chemistry was described using a 30 species-130 reaction model. The time variations of the electron energy distribution function, the species concentrations and the gas temperature were determined by solving the coupled set of the electron Boltzmann equation, species kinetics equations and a total energy equation. Some of the results obtained from the present model were compared to measurements previously carried out on the plasmas considered. Good agreement was obtained for the time variations of the gas temperature, the relative concentration of the H-atom and the intensities of the H α and the argon 750 nm emission lines. The effect of the duty cycle on the time-averaged composition and temperatures of the discharge was also studied. Results showed that moderate pressure H 2 /CH 4 pulsed discharges obtained at duty cycles of less than 20% show different behaviour than those obtained at higher duty cycles. In particular, while the plasma reaches the permanent periodic regime in less than 2 pulse-periods, i.e. 60 ms, for duty cycle values of less than 20%, long-time-scale density variations of hydrocarbon species, ions and electrons are obtained when this parameter is greater than 20%. The model was also used to determine if the use of a pulsed regime may bring some improvements in plasma-assisted diamond deposition processes. For this purpose we analysed the variation with duty cycle of the time-averaged populations of the H-atom and CH 3 that represent the key species for diamond deposition. Results showed that pulsed discharges with small duty cycle, of typically less than 20%, lead to a substantial enhancement of the time-averaged dissociation yield. On the other hand, the CH 3 concentration exhibits a strong decrease with the duty cycle. The methyl concentration in the investigated pulsed discharge is generally smaller than in continuous wave discharges obtained in the same reactor. These results indicate that short-pulse discharges would favour the formation of films with higher Raman quality, while long duty cycle pulsed discharges would enable deposition at higher growth rates.
physica status solidi (a), 2007
The use of pulsed discharges for diamond deposition has been demonstrated to ensure a better cont... more The use of pulsed discharges for diamond deposition has been demonstrated to ensure a better control of heat transfer from the plasma to the walls in microwave plasma reactors. It also favours the production of CH 3 species while keeping constant or higher the H-atom density. Higher growth rates can then be obtained. In this paper is reported an increase of the growth rate by 25% while decreasing the input microwave mean power by 15%. These results are discussed in terms of atomic hydrogen and methyl radicals densities calculated with a unstationary 1-D axial plasma model. The results show in particular that the gas temperature, which directly controls atomic hydrogen production, needs a t on of around 8ms to reach the steady state, and that 50% of atomic hydrogen is lost by recombination after a t off of 2ms.
Journal of Applied Physics, 2005
Microwave discharges of H2 admixed with CH4 in a moderate-pressure quartz bell jar reactor used f... more Microwave discharges of H2 admixed with CH4 in a moderate-pressure quartz bell jar reactor used for diamond deposition are studied numerically. Special attention was devoted to high-power densities which provide the most effective way for producing high-quality diamond films. First, a one-dimensional radial model describing the coupled phenomena of chemistry, energy transfer, as well as species and energy transport along the reactor's radial coordinate was developed. Species densities predicted with the model were compared with measurements with infrared tunable diode laser spectroscopy, resulting in validation of the model. Second, a one-dimensional axial model was used to describe the plasma flow along the reactor axis in a region between the reactor end wall and the substrate surface. This model was particularly useful for studying the plasma behavior in the vicinity of the substrate surface, where thermal and composition gradients are large. Both the radial and axial transport models are based on the same discharge model in which the plasma is described as a thermochemically nonequilibrium flow with different energy distributions for heavy species and electrons. The chemistry was described with a model containing 28 species and 131 reactions. The electron temperature, the gas temperature, and the species concentration were determined by solving a coupled set of equations. A wide range of experimental conditions used for diamond deposition was simulated, from low microwave power density (9 W cm-3, i.e., 600 W, 2500 Pa, and Tg~2200 K) to high-power density (30 W cm-3, i.e., 2 kW, 12 000 Pa, and Tg~3200 K). The main chemical paths were identified, and the major species, transport effects, and reaction pathways that govern diamond deposition plasmas are discussed.
Le Journal de Physique IV, 1991
Journal de Physique III, 1996
Diamond and Related Materials, 1998
Photoconductivity measurements on undoped diamond material can be strongly affected by the nature... more Photoconductivity measurements on undoped diamond material can be strongly affected by the nature of the electrical contacts, due to the wide band gap and high resistivity. We have used a contactless technique based on high frequency electrical measurements in order to probe the photoconductivity s HF-photo of CVD diamond films grown by a microwave assisted technique. Resonant methods, at 9.192 GHz are carried out in a microwave cavity by a reflection spectrometer. Samples are irradiated by modulated UV light. The photoconductivity s HF-photo is deduced from the variation of the quality factor and from the frequency shift. The samples studied were deposited under various growth conditions (temperature, gas mixture, etc.). The measured high frequency photoconductivity values were compared with the physical and electrical properties measured from conventional techniques (Raman spectroscopy, current-voltage and charged particle induced conductivity characterisation). The potential of this contactless high frequency measurement technique for CVD diamond characterisation is discussed.
Diamond and Related Materials, 2007
We report on electromagnetic simulations of an industrial thin film deposition process for hydrog... more We report on electromagnetic simulations of an industrial thin film deposition process for hydrogenated amorphous carbon using microwave plasmas.
Diamond and Related Materials, 1993
... regions as a function of the CH4 content of the feed gas and the deposition temperature (25 m... more ... regions as a function of the CH4 content of the feed gas and the deposition temperature (25 mbar, 600 W, 300 sccm, 4h). difference in Rz between alumina and SiC was less than 25%. The fact that diamond nucleated on the substrate when SiC was used for pretreatment of the ...
Journal of Physics: Condensed Matter, 2009
The unique properties of CVD diamond make it a compelling choice for high power electronics. In o... more The unique properties of CVD diamond make it a compelling choice for high power electronics. In order to achieve industrial use of CVD diamond, one must simultaneously obtain an excellent control of the film purity, very low defect content and a sufficiently rapid growth rate. Currently, only microwave plasma-assisted chemical vapour deposition (MPACVD) processes making use of resonant cavity systems provide enough atomic hydrogen to satisfy these requirements.