D. Ballutaud

The origin of visible photoluminescence from silicon oxide thin films prepared by dual-plasma chemical vapor deposition

In order to understand the radiative recombination mechanisms in silicon oxides, photoluminescence properties (PL) of H-rich amorphous silicon oxide thin films grown in a dual-plasma chemical vapor deposition reactor have been related to a number of stoichiometry and structure characterizations (x-ray photoelectron spectroscopy, vibrational spectroscopy, and gas evolution studies). The visible photoluminescence at room temperature from a-SiOx:H matrixes with different compositions, including different bonding environments for H atoms, has been studied in the as-deposited and annealed states up to 900 °C. Three commonly reported PL bands centered around 1.7, 2.1, and 2.9 eV have been detected from the same type of a-SiOx:H material, only by varying the oxygen content (x = 1.35, 1.65, and 2). Temperature quenching experiments are crucial to distinguish the 1.7 eV band, fully consistent with bandtail-to-bandtail recombination, from the radiative defect luminescence mechanisms attributed either to defects rel...

Hydrogen-acceptor interactions in diamond

Abstract Hydrogen-acceptor interactions are investigated in boron-doped diamond through deuterium diffusion experiments followed by SIMS measurements and through infrared absorption spectroscopy. From deuterium diffusion, we show that BD interactions can be properly demonstrated in low compensation B-doped homoepitaxial layers. However, the presence of defects in such layers strongly affects this interaction. The degree of passivation of boron acceptors by deuterium depends on the diffusion temperature. At 550°C or below, the B and D concentrations exactly match giving rise to a complete disappearance of the absorption bands related to the electronic transitions of neutral boron acceptors. Under thermal annealing above 500°C, (B,D) pairs dissociate and neutral boron acceptors recover. At deuterium diffusion temperatures of 700°C, the B passivation is absent.

Hydrogen in Monocrystalline CVD Boron Doped Diamond

The diffusion properties of hydrogen have been investigated in homoepitaxial layers of CVD boron doped diamond as a function of the diffusion temperature, the boron dopant concentration and the nature of the hydrogen source (rf or microwave plasma). Preliminary hydrogen effusion experiments on these hydrogenated samples are also reported. For both kinds of plasma we show that, below diffusion temperatures of 500 °C, the hydrogen diffusion is limited by trapping on boron acceptors. The onset of dissociation of B, H pairs occurs at 550 °C which implies a significantly higher stability of these pairs in diamond compared to silicon. However, a higher hydrogen diffusion activation energy is found in the microwave plasma exposed samples compared with the rf plasma exposed samples together with the absence of the subsurface hydrogen accumulation layer which is observed after rf plasma. Hydrogen effusion experiments show that in the rf plasma exposed samples the main effusion peak at 720 °C is attributed to the subsurface hydrogen accumulation layer. Another effusion peak at 850 °C is ascribed to the desorption of hydrogen adsorbed at the surface.

Semiconducting and magnetic properties of Zn1−xMnxO films grown by metalorganic chemical vapor deposition

Zn1−xMnxO diluted magnetic semiconductor single phase thin films have been grown by the MOCVD technique. Depositions have been done on fused silica and (0001)-sapphire substrates. Layers on silica are polycrystalline with [001] preferential orientation, while Zn1−xMnxO films on c-sapphire are highly (0001) textured. Manganese content (x) in the samples varies in 0.00–0.44 range. Change of c lattice parameter follows Vegard’s law. Hall effect measurements show a decrease of mobility with Mn increase and no change of carrier concentration. Optical transmission results present the increase of band gap with manganese incorporation. Superconducting quantum interference device magnetometry shows Curie–Weiss behaviors of the susceptibility with antiferromagnetic coupling with an effective exchange constant of J1∕kB=−16K.

Stoichiometry and infrared absorption of amorphous a-C1-xNx : H carbon nitride films

Stoichiometry, bonding configurations and structural properties of plasma-deposited hydrogen-rich amorphous carbon nitride a-C1−xNx:H (0<x<0.20) films have been investigated using infrared and Raman vibrational spectroscopies, along with x-ray photoemission spectroscopy at the C and N K-edges. With increasing N incorporation in a-C1−xNx:H, the total H content decreases slightly and C–H vibrations are progressively replaced by N–H vibrations. The dominant bonding configuration is C=N throughout the composition range, although C=N and C–N saturate above 10 N at. %, and C≡N configurations steadily increase throughout the stoichiometry range. A strong conjugation of imine (C=N) and nitrile (C≡N) groups with aromatic rings is evidenced while the Raman signature of the sp2 C phase indicates an increase in the D to G peak intensity ratio, related to some ordering of the sp2 clustered phase.

Hydrogen diffusion and stability in polycrystalline CVD undoped diamond

Abstract Diffusion profiles and effusion experiments performed on post-hydrogenated (deuterated) CVD diamond layers (grain size 2 and 0.2 μm) are reported in order to study the configurations and stability of hydrogen bonding in polycrystalline undoped CVD diamond. Deuterium is used as a tracer to improve the hydrogen detection limit. The diamond layers are first annealed at 1200°C in order to out-diffuse hydrogen present in the as-grown sample. Then the samples are exposed either to a radiofrequency plasma or a microwave plasma and the deuterium diffusion profiles are analyzed by secondary ion mass spectrometry. For r.f. and microwave plasma, the diffusion profiles are explained in term of trapping on plasma-induced defects near the surface and/or on inter- and intra-granular defects. The mean free paths of deuterium and capture radius of traps are calculated by fitting the deuterium diffusion profiles and depend on the grain sizes. Some CVD diamond layers are deposited using a gas mixture (CH 4 +D 2 ) and a deuterium concentration of 3×10 19 cm −3 , originating from the vector gas, is found in these as-grown samples. The stabilities of deuterium bonding in as-grown and post-deuterated samples are compared.

Electron energy loss spectroscopy determination of Ti oxidation state at the (001) LaAIO3/SrTiO3 interface as a function of LaAIO3 growth conditions

After the epitaxy of LaAlO3 on a TiO2-terminated {100} surface of SrTiO3, a high-mobility electron gas may appear, which has been the object of numerous works over the last four years. Its origin is a subject of debate between the interface polarity and unintended doping. Here we use electron energy loss spectrum images, recorded in cross-section in a scanning transmission electron microscope, to analyse the Ti3+ ratio, characteristic of extra electrons. We find an interface concentration of Ti3+ that depends on growth conditions.

Electron spin resonance study of hydrogenation effects in polycrystalline silicon

Electron spin resonance spectra obtained on polycrystalline silicon produced by annealing of chemical vapor deposition silicon are investigated before and after plasma hydrogenation of the material. Before hydrogenation, two paramagnetic defects are observed, one of them remaining unidentified (g=2.0084). Hydrogenation decreases the total spin density, but the two defects are affected differently; the defect with g=2.0084 is more efficiently passivated. The results are discussed in terms of the inter‐ and intragranular nature of the paramagnetic defects and of hydrogen diffusivity in the polycrystal.

Conversion of p-type to n-type diamond by exposure to a deuterium plasma

The lack of a shallow donor in diamond with reasonable room temperature conductivity has been a major obstacle, until now, for the realization of many diamond based electronic devices. Most recently it has been shown that exposure of p-type (B doped) homoepitaxial diamond layers to a deuterium plasma can result in the formation of n-type diamond with a shallow donor state (Ea=0.34eV) and high room temperature mobility (430cm2∕Vs) [Z. Teukam et al., Nat. Mater. 2, 482 (2003); C. Saguy et al., Diamond Relat. Mater. 13, 700 (2004)]. Experimental results, based on the comparison of secondary ion mass spectrometry profiles of B and D and Hall effect measurements at different temperatures are presented. They confirm the previous speculation that some deuterium related complex is responsible for the donor activity in diamond. These donors are shown to be formed in a two-step process. First, deuterium diffuses into the entire B containing layer rather slowly, being trapped by the boron acceptors and passivating t...

Hydrogen configurations and stability in amorphous sputtered silicon

The effects of the deposition parameters on configurations and stability of hydrogen (deuterium) in amorphous sputtered silicon a-Si:H have been analyzed using Fourier transformed infrared absorption spectroscopy, deuterium effusion experiments, and x-ray diffractometry. The ratio of monohydride bonds Si–H was calculated from the infrared absorption stretching mode spectrum. This ratio was increased when the substrate temperature was increased. The effusion results in a-Si:D, when deposited with a simple cathode, have shown the presence of clustered deuterium weak bonds in microvoids (400 °C deuterium effusion peak), beside isolated Si–D bonds embedded in the more compact tissue (650 °C deuterium effusion peak). The deconvolutions of the stretching mode infrared absorption spectrum of the as-grown sample and after isothermal annealing at 510 °C have allowed one to conclude that it is not possible to identify the low temperature and high temperature effusion peaks, respectively, with the decomposition of S...