TEM study of defects versus growth orientations in heavily boron-doped diamond

International audienceHeavy boron-doping layer in diamond can be responsible for the generation of extended defects during the growth processes (Blank et al., Diam. Relat. Mater. 17, 1840 (2008) [1]). As claimed recently (Alegre et al., Appl. Phys. Lett. 105, 173103 (2014) [2]), boron pair interactions rather than strain-related misfit seems to be responsible for such dislocation generation. In the present work, electron microscopy observations are used to study the defects induced by heavy boron doping in different growth plane orientations. Facets of pyramidal Hillocks (PHs) and pits provide access to non-conventional growth orientations where boron atoms incorporation is different during growth. TEM analysis on FIB prepared lamellas confirm that also for those growth orientations, the generation of dislocations occurs within the heavily boron-doped diamond layers. Stacking faults (SFs) have been also observed by high resolution transmission electron microscopy (HREM). From the invisibility criteria, using weak beam (WB) observation, ½ [1-10] and 1/6 [11-2], Burger vectors have been identified. Their generation behavior confirms the mechanism reported by Alegre et al. where local in-plane strain effects induced at the growing surface of the diamond lattice by the neighboring of several boron atoms cause the generation of such extended defects

Stratigraphy of a diamond epitaxial three-dimensional overgrowth using doping superlattices

International audienceThe selective doped overgrowth of 3D mesa patterns and trenches has become an essential fabrication step of advanced monolithic diamond-based power devices. A novel methodology is proposed here, combining the overgrowth of plasma-etched cylindrical mesa structures with the sequential growth of doping superlattices. The latter involve thin heavily boron doped epilayers separating thicker undoped epilayers in a periodic fashion. Beside the classical shape analysis under the scanning electron microscope relying on the appearance of facets corresponding to the main crystallographic directions and their evolution toward slow growing facets, the doping superlattices were used as markers in oriented cross-sectional lamellas prepared by Focused Ion Beam and observed by Transmission Electron Microscopy. This stratigraphic approach is shown here to be applicable to overgrown structures where faceting was not detectable. Intermediate growth directions were detected at different times of the growth process and the periodicity of the superlattice allowed to calculate the growth rates and parameters, providing an original insight into the planarization mechanism. Different configurations of the growth front were obtained for different sample orientations, illustrating the anisotropy of the 3D growth. Dislocations were also observed along the lateral growth fronts with two types of Burger vector: bsub01-1 = 1/2 [01-1] and bsub112 = 1/6 [112]. Moreover, the clustering of these extended defects in specific regions of the overgrowth prompted a proposal of two different dislocation generation mechanisms

Potential barrier heights at metal on oxygen-terminated diamond interfaces

International audienceElectrical properties of metal-semiconductor (M/SC) and metal/oxide/SC structures built with Zr or ZrO_2 deposited on oxygen-terminated surfaces of (001)-oriented diamond films, comprising a stack of lightly p-doped diamond on a heavily doped layer itself homoepitaxially grown on a Ib substrate, are investigated experimentally and compared to different models. In Schottky barrier diodes, the interfacial oxide layer evidenced by high resolution transmission electron microscopy and electron energy losses spectroscopy before and after annealing, and barrier height inhomogeneities accounts for the measured electrical characteristics until flat bands are reached, in accordance with a model which generalizes that of R.T. Tung [Phys. Rev. B 45, 13509 (1992)] and permits to extract physically meaningful parameters of the three kinds of interface: (a) unannealed ones; (b) annealed at 350°C; (c) annealed at 450°C, with characteristic barrier heights of 2.2-2.5 V in case (a) while as low as 0.96 V in case (c). Possible models of potential barriers for several metals deposited on well defined oxygen-terminated diamond surfaces are discussed and compared to experimental data. It is concluded that interface dipoles of several kinds present at these compound interfaces and their chemical evolution due to annealing are the suitable ingredients able to account for the Mott-Schottky behavior when the effect of the metal work function is ignored, and to justify the reverted slope observed regarding metal work function, in contrast to the trend always reported for all other metal-semiconductor interfaces.Les propriétés électriques et structurales d'interfaces métal/diamant et métal/oxyde/diamant où le métal est le Zirconium et le semi-conducteur comporte un empilement de couches faiblement et fortement dopées au bore sur substrat Ib, sont étudiées expérimentalement et comparées à différents modèles. Dans le barrière de Schottky, une inter-couche d'oxyde d'environ 2 couches atomiques, mise en évidence par diverses techniques de microscopie électronique à transmission, est présente et ajoutée à la présence d'inhomogénéités de barrière de potentiel, est corrélée aux propriétés électriques simulées par un modèle qui généralise celui de R. T. Tung [Phys. Rev. B 45, 13509 (1992)] . Les paramètres physiquement caractéristiques des interfaces (a) non recuites, (b) recuite à 350°C et (c) recuite à 450°C peuvent ainsi être extraits, en particulier des hauteurs de barrière de 2.2-2.5 V dans le cas (a) et aussi basses que 0.96 V dans le cas (c). Les modèles possibles de fixation du niveau de Fermi aux interfaces métal/diamant sont examinés et confrontés aux données récemment publiées pour différents métaux sur la surface oxygénée du diamant. On conclue que les quantités physiques judicieuses sont l'affinité électronique du diamant, fonction de son état de surface, pour justifier l'allure générale conforme au modèle de Mott-Schottky et la force du dipole d'interface, dépendante des liaisons chimiques à l'interface, pour expliquer la pente de la variation de la barrière en fonction du travail de sortie du métal, qui est inversée par rapport à tous les autres semi-conducteurs

Infrared study of the eta Chamaeleontis cluster and the longevity of circumstellar discs

We have analyzed JHKL observations of the stellar population of the ~9 Myr-old eta Chamaeleontis cluster. Using infrared (IR) colour-colour and colour-excess diagrams, we find the fraction of stellar systems with near-IR excess emission is 0.60 pm 0.13 (2_sigma). This results implies considerably longer disc lifetimes than found in some recent studies of other young stellar clusters. For the classical T Tauri (CTT) and weak-lined T Tauri (WTT) star population, we also find a strong correlation between the IR excess and H_alpha emission. The IR excesses of these stars indicate a wide range of star-disc activity; from a CTT star showing high levels of accretion, to CTT - WTT transition objects with evidence for some on-going accretion, and WTT stars with weak or absent IR excesses. Of the 15 known cluster members, 4 stars with IR excesses delta(K-L) > 0.4 mag are likely experiencing on-going accretion owing to strong or variable optical emission. The resulting accretion fraction (0.27 pm 0.13; 2_sigma) shows that the accretion phase, in addition to the discs themselves, can endure for at least ~10 Myr.Comment: 7 pages, 4 figures, accepted for MNRA

UBVI Surface Photometry of the Spiral Galaxy NGC 300 in the Sculptor Group

We present UBVI surface photometry for 20.'5 X 20.'5 area of a late-type spiral galaxy NGC 300. In order to understand the morphological properties and luminosity distribution characteristics of NGC 300, we have derived isophotal maps, surface brightness profiles, ellipticity profiles, position angle profiles, and color profiles. By merging the I-band data of our surface brightness measurements with those of Boeker et al. (2002) based on Hubble Space Telescope observations, we have made combined I-band surface brightness profiles for the region of 0."02 < r < 500" and decomposed the profiles into three components: a nucleus, a bulge, and an exponential disk.Comment: 16 pages(cjaa209.sty), Accepted by the Chinese J. Astron. Astrophys., Fig 2 and 8 are degraded to reduce spac

A Comparison of the Intrinsic Shapes of Two Different Types of Dwarf Galaxies: Blues Compact Dwarfs and Dwarf Ellipticals

We measure the apparent shapes for a sample of 62 blue compact dwarf galaxies (BCDs), and compare them with the apparent shapes for a sample of 80 dwarf elliptical galaxies (dEs). The BCDs are flatter, on average, than the dEs, but the difference is only marginally significant. We then use both non-parametric and parametric techniques to determine possible distributions of intrinsic shapes for the BCDs. The hypothesis that BCDs are oblate spheroids can be ruled out with a high confidence level ($> 99$), but the hypothesis that they are prolate spheroids cannot be excluded. The apparent shapes of BCDs are totally consistent with the hypothesis that they are triaxial ellipsoids. If the intrinsic axis ratios, $\beta$ and $\gamma$, are distributed according to a Gaussian with means $\beta_0$ and $\gamma_0$ and standard deviation $\sigma$, we find the best-fitting distribution for BCDs has $(\beta_0,\gamma_0,\sigma)= (0.66,0.55,0.16)$, while that for dEs has $(\beta_0,\gamma_0,\sigma)= (0.85,0.64,0.24)$. Our results are consistent with the hypothesis that BCDs have a close evolutionary relation with dEs.Comment: total 23 pages, 9 figures, and 1 Table, submitted to ApJ on Sep 19 1997. Email addresses: [email protected], [email protected], [email protected], [email protected], [email protected]

Electronic and physico-chemical properties of nanmetric boron delta-doped diamond structures

Heavily boron doped diamond epilayers with thicknesses ranging from 40 to less than 2 nm and buried between nominally undoped thicker layers have been grown in two different reactors. Two types of [100]-oriented single crystal diamond substrates were used after being characterized by X-ray white beam topography. The chemical composition and thickness of these so-called deltadoped structures have been studied by secondary ion mass spectrometry, transmission electron microscopy, and spectroscopic ellipsometry. Temperature-dependent Hall effect and four probe resistivity measurements have been performed on mesa-patterned Hall bars. The temperature dependence of the hole sheet carrier density and mobility has been investigated over a broad temperature range (6K<T<450 K). Depending on the sample, metallic or non-metallic behavior was observed. A hopping conduction mechanism with an anomalous hopping exponent was detected in the non-metallic samples. All metallic delta-doped layers exhibited the same mobility value, around 3.660.8 cm2/Vs, independently of the layer thickness and the substrate type. Comparison with previously published data and theoretical calculations showed that scattering by ionized impurities explained only partially this low common value. None of the delta-layers showed any sign of confinement-induced mobility enhancement, even for thicknesses lower than 2 nm.14 page

Suppression of stored-beam oscillation and observation of flux improvement during top-up injection

This paper describes a start-to-end study of the suppression of stored-beam oscillation during top-up injection at the Pohang Light Source (PLS-II) beam line. The fast counterkicker implemented in PLS-II suppresses stored-beam oscillations in the vertical plane. During top-up injection in the magnetic spectroscopy beam line of PLS-II, flux improvement due to the suppression of stored-beam oscillation was clearly observed.11Ysciescopu

Evidence for the decay B0->eta pi^0

We report a search for the charmless hadronic decay $B^0\to\eta \pi^0$ with a data sample corresponding to an integrated luminosity of 694 $\rm fb^{-1}$ containing $753\times10^6$ $B\bar{B}$ pairs. The data were collected by the Belle experiment running on the $\Upsilon(4S)$ resonance at the KEKB $e^+e^-$ collider. We measure a branching fraction $\mathcal{B}(B^0\to\eta\pi^0)=(4.1^{+1.7+0.5}_{-1.5-0.7})\times 10^{-7}$, where the first uncertainty is statistical and the second is systematic. Our measurement gives an upper limit of $\mathcal{B}(B^0\to\eta\pi^0)<6.5\times 10^{-7}$ at 90\% confidence level. The signal has a significance of $3.0$ standard deviations and constitutes the first evidence for this decay mode.Comment: 11 pages, 3 figures, 2 tables, submitted to Physical Review D(R

Selectively boron doped homoepitaxial diamond growth for power device applications

Diamond lateral growth is a powerful technique for the design and fabrication of diamond-based power electronic devices. Growth orientation affects the diamond deposition in terms of growth rate, surface roughness, and impurity incorporation. It has been shown that the finally grown surface of a patterned substrate can be predesigned based on the growth conditions. Thus, simultaneous growth along different surface orientations yields regions with different properties. In line with this, the incorporation of boron in a microwave plasma enhanced chemical vapor deposition laterally deposited epilayer over a mesa patterned {100}-oriented diamond substrate was studied by cathodoluminescence. It was observed that laterally oriented facets were highly boron doped in contrast to the {100}-oriented surfaces, which did not show any bound exciton emission, related to the doping. This study shows that, by designing the initial pattern and tuning the conditions, it is possible to drive a selective incorporation of boron into the grown layer