Schottky Contacts on Polarity-Controlled Vertical ZnO Nanorods

Polarity-controlled growth of ZnO by chemical bath deposition provides a method for controlling the crystal orientation of vertical arrays of nanorods. The ability to define the morphology and structure of the nanorods is essential to maximising the performance of optical and electrical devices such as piezoelectric nanogenerators; however, well-defined Schottky contacts to the polar facets of the structures have yet to be explored. In this work, we demonstrate a process to fabricate metal-semiconductor-metal device structures from vertical arrays with Au contacts on the uppermost polar facets of the nanorods and show the O-polar nanorods (~0.44 eV) have a greater effective barrier height than the Zn-polar nanorods (~0.37 eV). Oxygen plasma treatment is shown by Cathodoluminescence (CL) spectroscopy to reduce mid-gap defects associated with radiative emissions that improves the Schottky contacts from weakly-rectifying to strongly-rectifying. Interestingly, the plasma treatment was shown to have a much greater effect in reducing the number of carriers in O-polar nanorods through quenching of the donor-type substitutional hydrogen on oxygen sites (HO) when compared to the zinc vacancy related hydrogen defect complexes (VZn, Hn) in Zn-polar nanorods that evolve to lower coordinated complexes. The effect on HO in the O-polar nanorods coincided with a large reduction in the visible range defects producing a lower conductivity and creating the larger effective barrier heights. This combination can allow radiative losses and charge leakage to be controlled enhancing devices such as dynamic photodetectors, strain sensors, and LEDs while showing the O-polar nanorods can outperform Zn-polar nanorods in such applications

High conductivity in Si-doped GaN wires

4 pagesInternational audienceTemperature-dependent resistivity measurements have been performed on single Si-doped GaN microwires grown by catalyst-free metal-organic vapour phase epitaxy. Metal-like conduction is observed from four-probe measurements without any temperature dependence between 10 K and 300 K. Radius-dependent resistivity measurements yield resistivity values as low as 0.37 mohm.cm. This is in agreement with the full width at half maximum (170 meV) of the near band edge luminescence obtained from low temperature cathodoluminescence study. Higher dopant incorporation during wire growth as compared to conventional epitaxial planar case is suggested to beresponsiblefortheuniqueconductivity

Thermoelectric and micro-Raman measurements of carrier density and mobility in heavily Si-doped GaN wires

International audienceCombined thermoelectric-resistivity measurements and micro-Raman experiments have been performed on single heavily Si-doped GaN wires. In both approaches, similar carrier concentration and mobility were determined taking into account the non-parabolicity of the conduction band. The unique high conductivity of Si-doped GaN wires is explained by a mobility µ=56 cm2 /V s at a carrier concentration n = 2.6 10^20 /cm 3. This is attributed to a more efficient dopant incorporation in Si-doped GaN microwires as compared to Si-doped GaN planar layers. (c) 2013 AIP Publishing LLC

Optical properties of single ZnTe nanowires grown at low temperature

Optically active gold-catalyzed ZnTe nanowires have been grown by molecular beam epitaxy, on a ZnTe(111) buffer layer, at low temperature 350\degree under Te rich conditions, and at ultra-low density (from 1 to 5 nanowires per micrometer^{2}. The crystalline structure is zinc blende as identified by transmission electron microscopy. All nanowires are tapered and the majority of them are oriented. Low temperature micro-photoluminescence and cathodoluminescence experiments have been performed on single nanowires. We observe a narrow emission line with a blue-shift of 2 or 3 meV with respect to the exciton energy in bulk ZnTe. This shift is attributed to the strain induced by a 5 nm-thick oxide layer covering the nanowires, and this assumption is supported by a quantitative estimation of the strain in the nanowires

Exciton diffusion coefficient measurement in ZnO nanowires under electron beam irradiation

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A single-step electron beam lithography of buried nanostructures using cathodoluminescence imaging and low temperature

International audienceWe report a new electron beam lithography process using the cathodoluminescence properties of semiconductors to visualize nanostructures buried underneath the resist and to subsequently write the pattern associated with these nanostructures. This single-step process could be used, for example, to make electrical contacts to nanowires (as illustrated in this work) or to design a photonic crystal resonator centered on a single quantum dot. Fabrication speed and positioning accuracy are significantly increased as compared to the standard process since no alignment marks and the mapping step of the nanostructures with respect to these marks are needed. We show also that low temperature (down to 5 K) could be used to improve the observation of the nanostructures through the resist while keeping very good spatial resolution

Procédé de lithographie électronique a imagerie de cathodoluminescence

Procédé de lithographie électronique pour la réalisation de dispositifs incluant des objets de dimensions micrométriques ou nanométriques déposés ou intégrés sur un substrat, comportant : a) le dépôt d'une couche de résine au-dessus d'une surface dudit substrat; b) l'insolation de la résine par balayage d'un faisceau d'électrons pour libérer sélectivement des régions prédéfinies de la résine; c) le développement de la résine insolée pour libérer sélectivement des régions prédéfinies de ladite surface; et d) la fabrication du dispositif par gravure et/ou dépôt de matière à travers le masque de résine ainsi obtenu; caractérisé en ce qu'il comporte également, après dépôt de la résine mais préalablement à son insolation, l'acquisition d'une image dudit objet obtenue par balayage de la surface du substrat par un faisceau d'électrons à une dose insuffisante pour insoler la résine, et par détection de la cathodoluminescence ainsi induite; ladite image étant utilisée pour le pilotage du faisceau d'électrons lors de ladite étape d'insolation

Heteroepitaxy of Scandium Delafossite on ZnO

International audienceThe trigonal polytypes of the delafossites ScCuO 2+δ and Sc 1−x Mg x CuO 2+δ , which are p-type semiconductors, are elaborated by pulse laser deposition and epitaxially grown on the oxygen terminated (001) ZnO surface along their same basal plane with an absolute mismatch less than 0.5 %. Depending on the Mg content x and excess intercalated oxygen δ, the relative mismatch can be either positive or negative, but very close to zero in any cases. Optically excited transitions between valence band and conduction band states detected from spectroscopic ellipsometry and cathodoluminescence spectrum confirm the band structure calculated theoretically by several authors. The deviation between fundamental optical absorption and exciton radiative recombination yields an exciton binding energy of 0.2 eV