Marie-Laure David

Electrically active defects in irradiated 4H-SiC

4H-SiC epilayers were irradiated with either protons or electrons and electrically active defects were studied by means of deep level transient spectroscopy. Motion of defects has been found to occur at temperature as low as 350–400 K. Indeed, the application of an electric field has been found to enhance modifications in defect concentrations that can also occur during long time annealing at elevated temperature. Two levels have been revealed and labeled B and M. Two other levels, referred to as S1 and S2 and located at 0.40 and 0.71 eV below the conduction band edge have been studied in detail (capture cross sections, profiling, formation energy, activation energy during annealing). The S1 and S2 levels have been found to exhibit a one to one relation and are proposed to be two charge states of the same acceptor center, labeled the S center.

Effect of implant temperature on defects created using high fluence of helium in silicon

Extended defects formed by high-fluence helium implantation in silicon have been studied as a function of the implantation temperature, from room temperature up to 800u200a°C. Transmission electron microscopy results show that the formation of cavities created by a 50 keV He implantation with a fluence of 5×1016u2009cm−2 can be divided into three stages. For implantation temperature up to about 300u200a°C the bubble size is relatively constant but the bubble density decreases due to the increase in dynamic annealing. Above 300u200a°C, where divacancies are no longer stable and when the helium is mobile, both the density and size of the cavities stay relatively constant. In this stage, helium starts to diffuse out and the cavities become more and more faceted as the temperature increases. Concurrently interstitial-type defects appear: small elongated rod-like defects at relatively low temperatures and large ribbon-like defects at 600u200a°C. Finally, for implantation at 800u200a°C, no cavities are formed and only dislocation loops and {113}’s (ribbon-like defects and rod-like defects), are observed depending on the deposited energy profile. At this temperature the defect annealing during implantation becomes efficient to convert ribbon-like defects into dislocation loops.Extended defects formed by high-fluence helium implantation in silicon have been studied as a function of the implantation temperature, from room temperature up to 800u200a°C. Transmission electron microscopy results show that the formation of cavities created by a 50 keV He implantation with a fluence of 5×1016u2009cm−2 can be divided into three stages. For implantation temperature up to about 300u200a°C the bubble size is relatively constant but the bubble density decreases due to the increase in dynamic annealing. Above 300u200a°C, where divacancies are no longer stable and when the helium is mobile, both the density and size of the cavities stay relatively constant. In this stage, helium starts to diffuse out and the cavities become more and more faceted as the temperature increases. Concurrently interstitial-type defects appear: small elongated rod-like defects at relatively low temperatures and large ribbon-like defects at 600u200a°C. Finally, for implantation at 800u200a°C, no cavities are formed and only dislocation loop...

Formation of bubbles by high dose He implantation in 4H–SiC

1.6 MeV He+ ions were implanted at room temperature into (0001)Si n-type 4H–SiC at a dose of 1×1017u2009cm−2. Cross-section transmission electron microscopy (TEM) and x-ray diffraction (XRD) were used to characterize the induced defects and the strain-induced effects before and after annealing. Infrared reflectivity was also used to localize changes in the microstructure. In the as-implanted samples, the TEM observations show a three layer damaged region consisting of a continuous amorphous layer surrounded with two buried crystalline zones. Bubbles of small diameter are readily formed in the as-implanted state. Only a few changes are observed after a 800u200a°C-30 min annealing. Voids formation and recrystallization of the amorphous state in different polytypes are observed for a 1500u200a°C-30 min annealing. Moreover, XRD shows that the dilatation of the c axis of the lattice observed after implantation completely disappears after the high temperature annealing implying the structural recovery of all the crystallin...

In situ probing of helium desorption from individual nanobubbles under electron irradiation

The understanding of the mechanisms of helium bubble formation and evolution in materials requires the quantitative determination of several key quantities such as the helium density in the bubbles. Helium nanobubbles of about 16 nm in diameter were created in silicon by helium implantation at high fluence and subsequent annealing. Individual nanobubbles were analyzed by spatially resolved Electron Energy-loss Spectroscopy (EELS). We report on the in situ probing of helium desorption from the nanobubbles under electron irradiation. This opens new perspectives for a more accurate determination of the helium density through spatially resolved EELS.

An IR-reflectivity and X-ray diffraction study of high energy He-ion implantation-induced damage in 4H-SiC

Abstract Due to recent progress in silicon carbide (SiC) technology, understanding the behaviour of defects in SiC is a crucial challenge for the industrial development of SiC-based devices. High energy helium ion implantation at high fluence in SiC creates a few microns deep damaged layers with nanocavities which are expected to play an important role in gettering of unwanted impurities. Post-implantation evolution of the ion implantation-induced damage is then controlled by thermal annealing. Results of an infrared reflectivity (IRR) and X-ray diffraction (XRD) study of ion implantation-induced damage in crystalline (0xa00xa00xa01) n-type 4H–SiC implanted at room temperature with 1.6 MeV He + ions at the fluence of 10 17 cm −2 show the formation of two layers above the unperturbed crystal: a 3.4 μm deep defective strained surface layer on a 0.4 μm thick strongly perturbed interface layer. Thermal annealing at 1500 °C for 30 min under high vacuum was shown to induce structural recovery of the surface layer.

On the effects of implantation temperature in helium implanted silicon

He+ ions were implanted into silicon with a fluence of 5×10 16?cm?2 at different temperatures ranging from 473 to 1073 K. Samples were analyzed by thermal helium desorption spectroscopy and by transmission electron microscopy. As far as cavity formation is concerned, the behavior can be divided into three stages depending on the implantation temperature. However, it is found that helium release from cavities is governed by a single mechanism regardless of the implantation temperature.

Evidence for Two Charge States of the S-Center in Ion-Implanted 4H-SiC

Proton-implanted 4H-SiC samples of n-type, have been investigated using Deep Level Transient Spectroscopy (DLTS). Two levels, referred to as S 1 and S2 have been studied in detail. S 1 and S2 are located, respectively, at 0.41 eV and 0.71 eV below the conduction band edg e. Their extrapolated capture cross-sections are both ∼5x10cm. Furthermore, isochronal annealing performed between 350 and 625K have shown a close one-to-one correlation betwee n the concentration of the two levels. Our results suggest strongly that these levels represent two charge states of the S-center, and the absence of a Pool-Frenkel effect indicates a cent r of acceptor type.

The effect of the substrate temperature on extended defects created by hydrogen implantation in germanium

H implantation in Ge was carried out at two substrate temperatures, room temperature (RT) and 150u2009°C. The microstructure of the as-implanted Ge samples was studied by transmission electron microscopy and grazing incidence small-angle x-ray scattering. Small (001) and {111} platelets and {113} defects are nucleated at RT. For higher substrate temperature, microcracks, cavities, and platelike cavity clusters are created as well. The formation of these types of defects is ascribed to the interplay between dynamic and kinetic effects occurring during the implantation.

In situ controlled modification of the helium density in single helium-filled nanobubbles

We demonstrate that the helium density and corresponding pressure can be modified in single nano-scale bubbles embedded in semiconductors by using the electron beam of a scanning transmission electron microscope as a multifunctional probe: the measurement probe for imaging and chemical analysis and the irradiation source to modify concomitantly the pressure in a controllable way by fine tuning of the electron beam parameters. The control of the detrapping rate is achieved by varying the experimental conditions. The underlying physical mechanisms are discussed; our experimental observations suggest that the helium detrapping from bubbles could be interpreted in terms of direct ballistic collisions, leading to the ejection of the helium atoms from the bubble.

Effect of pressure and stress on blistering induced by hydrogen implantation in silicon

Silicon wafers have been implanted with hydrogen at high fluence and buckling structures have been observed after thermal treatments. The effects of both internal pressure and residual stresses on the blistering have been then investigated in the framework of the Foppl-von Karman theory of thin plates and the buckle profiles have been determined. The internal pressure inside the cavities resulting from the implantation conditions is finally derived with the help of the experimental profiles of the buckles.