RESUMO
Bottom-up fabrication of nanowire-based devices is highly attractive for oxide photonic devices because of high light extraction efficiency; however, unsatisfactory electrical injection into ZnO and poor carrier transport properties of nanowires severely limit their practical applications. Here, we demonstrate that ZnO nanorods doped with Ga donors by in situ dopant incorporation during vapour-solid growth exhibit superior optoelectronic properties that exceed those currently synthesised by chemical vapour deposition, and accordingly can be electrically integrated into Si-based photonic devices. Significantly, the doping method was found to improve the nanorod quality by decreasing the concentration of point defects. Light-emitting diodes (LEDs) fabricated from the Ga-doped ZnO nanorod/p-Si heterojunction display bright and colour-tunable electroluminescence (EL). These nanorod LEDs possess a dramatically enhanced performance and an order of magnitude higher EL compared with equivalent devices fabricated with undoped nanorods. These results point to an effective route for large-scale fabrication of conductive, single-crystalline ZnO nanorods for photonic and optoelectronic applications.
RESUMO
TaRh2B2 and NbRh2B2 compounds exhibit noncentrosymmetric superconductivity with a chiral structure. Density functional theory-based ab-initio calculations have been executed to analyze the structural properties, mechanical stability, ductility/brittleness behaviors, Debye temperature, melting temperature, optical response to incident photon energy, electronic characteristics, and superconducting transition temperature of chiral TaRh2B2 and NbRh2B2 compounds under pressure up to 16 GPa. Both the chiral phases are mechanically stable and exhibit ductile nature under the studied pressure. The maximum value of the Pugh ratio (an indicator of ductile/brittle behaviors) is observed to be 2.55 (for NbRh2B2) and 2.52 (for TaRh2B2) at 16 GPa. The lowest value of the Pugh ratio is noticed at 0 GPa for both these chiral compounds. The analysis of reflectivity spectra suggests that both the chiral compounds can be used as efficient reflecting materials in the visible energy region. At 0 GPa, the calculated densities of states (DOSs) at the Fermi level are found to be 1.59 and 2.13 states eV-1 per formula unit for TaRh2B2 and NbRh2B2, respectively. The DOS values of both the chiral phases do not alter significantly with applied pressure. The shape of the DOS curve of both compounds remains almost invariant with applied pressure. The pressure-induced variation of Debye temperatures of both compounds is observed, which may cause the alternation of the superconducting transition temperature, Tc, with applied pressure. The probable changing of Tc with pressure has been analyzed from the McMillan equation.
RESUMO
Undoped and Ga-doped ZnO films were grown on c-sapphire using pulsed laser deposition (PLD) at the substrate temperature of 600 °C. Positron annihilation spectroscopy study (PAS) shows that the dominant VZn-related defect in the as-grown undoped ZnO grown with relative low oxygen pressure P(O2) is a vacancy cluster (most likely a VZn-nVO complex with n = 2, 3) rather than the isolated VZn which has a lower formation energy. Annealing these samples at 900 °C induces out-diffusion of Zn from the ZnO film into the sapphire creating the VZn at the film/sapphire interface, which favors the formation of vacancy cluster containing relatively more VZn. Increasing the P(O2) during growth also lead to the formation of the vacancy cluster with relatively more VZn. For Ga-doped ZnO films, the oxygen pressure during growth has significant influence on the electron concentration and the microstructure of the VZn-related defect. Green luminescence (GL) and yellow luminescence (YL) were identified in the cathodoluminescence study (CL) study, and both emission bands were quenched after hydrogen plasma treatment. The origin of the GL is discussed.