GaN nanowires have been grown by molecular beam epitaxy either catalyst-free or catalyst-induced by means of Ni seeds.Under identical growth conditions of temperature andⅤ/Ⅲratio,both types of GaN nanowires are of w...GaN nanowires have been grown by molecular beam epitaxy either catalyst-free or catalyst-induced by means of Ni seeds.Under identical growth conditions of temperature andⅤ/Ⅲratio,both types of GaN nanowires are of wurtzite structure elongated in the Ga-polar direction and are constricted by M-plane facets.However,the catalyst-induced nanowires contain many more basal-plane stacking faults and their photoluminescence is weaker.These differences can be explained as effects of the catalyst Ni seeds.展开更多
Tapering of vapour-liquid-solid （VLS） grown nanowires （NWs） is a widespread phenomenon resulting from dynamics of the liquid droplet during growth and direct vapour-solid （VS） growth on the sidewall. To investig...Tapering of vapour-liquid-solid （VLS） grown nanowires （NWs） is a widespread phenomenon resulting from dynamics of the liquid droplet during growth and direct vapour-solid （VS） growth on the sidewall. To investigate both effects in a highly controlled wa35 we developed a novel two-step growth approach for the selective area growth （SAG） of GaAs nanowires （NWs） by molecular beam epitaxy. In this growth approach optimum growth parameters are provided for the nucleation of NWs in a first step and for the shape variation during elongation in a second step, allowing NWs with a thin diameter （45 nrn） and an untapered morphology to be realized with high vertical yield. We quantify the flux dependence of radial VS growth and build a model that takes into account diffusion on the NW sidewalls to explain the observed VS growth rates. As our model is consistent with axial VLS growth we can combine it with an existing model for the diameter variation due to the droplet dynamics at the NW top. Thereby, we achieve full understanding of the diameter of NWs over their entire length and the evolution of the diameter and tapering during growth. We conclude that only the combination of droplet dynamics and VS growth results in an untapered morphology. This result enables NW shape engineering and has important implications for doping of NWs.展开更多
Single,free-standing GaN nanowires grown by plasma-assisted molecular-beam epitaxy have been investigated with low temperature micro-photoluminescence.The quantitative analysis of the luminescence spectra of around 10...Single,free-standing GaN nanowires grown by plasma-assisted molecular-beam epitaxy have been investigated with low temperature micro-photoluminescence.The quantitative analysis of the luminescence spectra of around 100 nanowires revealed that each nanowire exhibits its own individual spectrum.A significant fraction of nanowires exclusively emits at energies corresponding to either surface-donor-bound or free excitons,demonstrating that optical properties of individual nanowires are determined by a few impurity atoms alone.The number of impurities per nanowire and their location within the nanowires varies according to Poissonian statistics.展开更多
基金This work has been supported by the EU through the IST project NODE(No.015783)the Marie Curie RTN PARSEM(MRTN-CT-2004-005583).
文摘GaN nanowires have been grown by molecular beam epitaxy either catalyst-free or catalyst-induced by means of Ni seeds.Under identical growth conditions of temperature andⅤ/Ⅲratio,both types of GaN nanowires are of wurtzite structure elongated in the Ga-polar direction and are constricted by M-plane facets.However,the catalyst-induced nanowires contain many more basal-plane stacking faults and their photoluminescence is weaker.These differences can be explained as effects of the catalyst Ni seeds.
文摘Tapering of vapour-liquid-solid （VLS） grown nanowires （NWs） is a widespread phenomenon resulting from dynamics of the liquid droplet during growth and direct vapour-solid （VS） growth on the sidewall. To investigate both effects in a highly controlled wa35 we developed a novel two-step growth approach for the selective area growth （SAG） of GaAs nanowires （NWs） by molecular beam epitaxy. In this growth approach optimum growth parameters are provided for the nucleation of NWs in a first step and for the shape variation during elongation in a second step, allowing NWs with a thin diameter （45 nrn） and an untapered morphology to be realized with high vertical yield. We quantify the flux dependence of radial VS growth and build a model that takes into account diffusion on the NW sidewalls to explain the observed VS growth rates. As our model is consistent with axial VLS growth we can combine it with an existing model for the diameter variation due to the droplet dynamics at the NW top. Thereby, we achieve full understanding of the diameter of NWs over their entire length and the evolution of the diameter and tapering during growth. We conclude that only the combination of droplet dynamics and VS growth results in an untapered morphology. This result enables NW shape engineering and has important implications for doping of NWs.
基金This work was partially supported by the EU Marie Curie RTN contract MRTN-CT-2004-005583(PARSEM)and by the IST project NODE 015783.
文摘Single,free-standing GaN nanowires grown by plasma-assisted molecular-beam epitaxy have been investigated with low temperature micro-photoluminescence.The quantitative analysis of the luminescence spectra of around 100 nanowires revealed that each nanowire exhibits its own individual spectrum.A significant fraction of nanowires exclusively emits at energies corresponding to either surface-donor-bound or free excitons,demonstrating that optical properties of individual nanowires are determined by a few impurity atoms alone.The number of impurities per nanowire and their location within the nanowires varies according to Poissonian statistics.
