Jean-Marie Bluet

Application of 3C-SiC quantum dots for living cell imaging

Highly luminescent, stable, and biocompatible 3C-SiC quantum dots (QDs) with no protective shells have been applied for fluorescence imaging of biological living cells. Structural and luminescent properties of the 3C-SiC QDs are described. Marking of the living cells with such QDs highlights the penetration, accumulation, and heterogeneous distribution of the QDs inside the intracellular space.

Current deep level transient spectroscopy analysis of AlInN/GaN high electron mobility transistors: Mechanism of gate leakage

In order to assess possible mechanisms of gate reverse-bias leakage current in AlInN/GaN high electron mobility transistors (HEMTs) grown by metalorganic chemical-vapor deposition on SiC substrates, temperature-dependent current-voltage measurements combined with Fourier transform current deep level transient spectroscopy (FT-CDLTS) are performed in the temperature range of 200–400 K. In this range of temperature reverse-bias leakage current flow is found to be dominated by Poole–Frenkel emission. Based on CDLTS measurements, a model of leakage current transport via a trap state located at the AlInN/metal interface with an activation energy of 0.37 eV is suggested. The trap nature is shown to be an extended trap, most probably associated with dislocations in the AlInN barrier layer.

Influence of the interfacial chemical environment on the luminescence of 3CSiC nanoparticles

Surface chemistry of as-prepared 3CSiC nanoparticles obtained by electrochemical etching of bulk 3CSiC substrates was studied. Chemical environment was found to influence strongly the photoinduced electronic transitions in the 3CSiC nanoparticles. The influence of different interfacial chemical environments of the 3CSiC nanoparticles, such as surface chemistry, solvent nature, and surface charges on the photoinduced absorption and luminescence of the nanoparticles at room temperature, is described and discussed in detail. For example, oxidation induced passivation of the radiative band gap states allows visualization of the transitions between energy levels in the nanoparticles in which photogenerated charge carriers are quantumly confined. Electrostatic screening of the radiative band gap states by highly polar solvent media leads to a blueshift and a decrease in the width at half maximum of the photoluminescence spectra of the nanoparticles. As for the surface charges, they govern band bending slope...

Activation of aluminum implanted at high doses in 4H–SiC

We report an investigation of the electrical activation of aluminum implanted at high dose in 4H–SiC. We show that at reasonably high temperature implantation and annealing conditions, one activates about 37.5% of the implanted species. Of course, the final (concentration-dependent) activation ratio differs slightly from this average value but varies only between 0.5 and 0.25 when the targeted concentration increases from 3.33×1018 to 1021 cm−3. Provided a standard mobility can be maintained, this results in fairly low sheet resistance. The best (lowest) value obtained in this work is 15 mΩ cm at 700 K (95 mΩ cm at room temperature) for a 190-nm-thick layer implanted with 1021 atoms cm−3. In MESA-etched p–n junctions with a 100 μm diameter, this resulted in a typical on-resistance of 1.5 mΩ cm2, mainly limited by the substrate and n− epitaxial layer.

Photoluminescence of 6H–SiC nanostructures fabricated by electrochemical etching

Photoluminescence (PL) spectra of 6H–SiC nanostructures (nanoporous layers and nanopowder) fabricated by electrochemical etching of bulk wafers consist of broad subgap emission bands as well as above-gap tails. These features are explained, respectively, in terms of radiative recombinations via N–Al donor-acceptor electronic levels and surface states as well as quantum confinement phenomenon in small nanocrystallites. An excitation power dependent PL study allowed differentiation of the radiative channels mentioned above. The particular role of surface states on the room temperature PL of the SiC nanopowder is highlighted. A concentration dependent PL study on aqueous suspensions of the nanopowder points out the quenching of PL emission coming from recombination of quantum-confined excitons in small SiC nanoparticles interacting with the larger ones.

Amorphization and reduction of thermal conductivity in porous silicon by irradiation with swift heavy ions

In this article, we demonstrate that the thermal conductivity of nanostructured porous silicon is reduced by amorphization and also that this amorphous phase in porous silicon can be created by swift (high-energy) heavy ion irradiation. Porous silicon samples with 41%-75% porosity are irradiated with 110 MeV uranium ions at six different fluences. Structural characterisation by micro-Raman spectroscopy and SEM imaging show that swift heavy ion irradiation causes the creation of an amorphous phase in porous Si but without suppressing its porous structure. We demonstrate that the amorphization of porous silicon is caused by electronic-regime interactions, which is the first time such an effect is obtained in crystalline silicon with single-ion species. Furthermore, the impact on the thermal conductivity of porous silicon is studied by micro-Raman spectroscopy and scanning thermal microscopy. The creation of an amorphous phase in porous silicon leads to a reduction of its thermal conductivity, up to a factor of 3 compared to the non-irradiated sample. Therefore, this technique could be used to enhance the thermal insulation properties of porous Si. Finally, we show that this treatment can be combined with pre-oxidation at 300 °C, which is known to lower the thermal conductivity of porous Si, in order to obtain an even greater reduction.

Traps centers and deep defects contribution in current instabilities for AlGaN/GaN HEMT's on silicon and sapphire substrates

Abstract AlGaN/GaN high electron mobility transistors (HEMTs) with Si and Al 2 O 3 substrates reveals anomalies on I ds – V ds – T and I gs – V gs – T characteristics (degradation in drain current, kink effect, barrier height fluctuations, etc.). Stress and random telegraph signal (RTS) measurements prove the presence of trap centers responsible for drain current degradation. An explanation of the trapping mechanism responsible for current instabilities is proposed. Deep defects analysis performed by capacitance transient spectroscopy ( C -DLTS), frequency dispersion of the output conductance ( G ds ( f )), respectively, on gate/source and drain/source contacts and RTS prove the presence of deep defects localized, respectively, in the gate and in the channel regions. Defects detected by C -DLTS and G ds ( f ) are strongly correlated, respectively, to barrier height inhomogeneities and kink anomalies. Gate current analysis confirms the presence of ( G – R ) centers acting like traps at the interface GaN/AlGaN. Finally, the localization of these traps defects is proposed.

Characterization of the thermal conductivity of insulating thin films by scanning thermal microscopy

This paper reports on the abilities of a Scanning Thermal Microscopy (SThM) method to characterize the thermal conductivity of insulating materials and thin films used in microelectronics and microsystems. It gives a review of the previous works on the subject and gives new results allowing showing the performance of a new method proposed for reducing the thermal conductivity of meso-porous silicon by swift heavy ion irradiation. Meso-porous silicon samples were prepared by anodisation of silicon wafers and underwent irradiation by 845MeV ^2^0^8Pb ions, with fluences of 4x10^1^1 and 7x10^1^1cm^-^2. Thermal measurements show that irradiation reduced thermal conductivity by a factor of up to 2.

Strain dependence of indirect band gap for strained silicon on insulator wafers

We have used low temperature photoluminescence measurements in order to quantify the impact of strain effect on the Si indirect band gap in 9 nm thick tensely strained silicon on insulator layers. A redshift of the transverse optical phonon excitonic recombination in the strained silicon layer was evidenced as the strain in the layer is increased. Band gap shrinkages in the Δ direction equal to 130±3 meV, 184±3 meV, and 239±3 meV were obtained for 0.87±0.03%, 1.22±0.05%, and 1.54±0.06% strain values. These measured indirect transitions are in good agreement with the calculated strained silicon indirect band gap values.

Photoluminescence of silicon nanoparticles chemically modified by alkyl groups and dispersed in low-polar liquids

A detailed comparative analysis of photoluminescence behavior of silicon nanoparticles in air and dispersed in low-polar liquids is reported. Efficient dispersion and excellent stability of the chemically modified nanoparticles in low-polar liquids are achieved. Influence of the chemical functionalization and of the low-polar liquids on steady-state and time-resolved photoluminescence of the silicon nanoparticles is investigated. Role of low-polar liquids on recombination mechanisms taking place in the nanoparticles is discussed in terms of Förster resonant energy transfer processes. Effect of exciting laser power on photoluminescence spectra of the silicon nanoparticles both in air and in low-polar liquids is investigated and the electronic mechanisms involved into the observed phenomena are discussed.