Exciton-Related Electroluminescence from ZnO Nanowire Light-Emitting Diodes

The authors study the microscopic origin of the electroluminescence from zinc oxide (ZnO) nanowire light-emitting diodes (LEDs) fabricated on a heavily doped p-type silicon (p-Si) substrate. By comparing the low-temperature photoluminescence and electroluminescence of a single nanowire LED, bound- and free-exciton related recombination processes, together with their longitudinal-optical phonon replicas, can be identified as the origin of both electroluminescence and photoluminescence.Engineering and Applied Science

A Combination of Ion Implantation and High-Temperature Annealing: The Origin of the 265 nm Absorption in AlN

The commonly observed absorption around 265 nm in AlN is hampering the outcoupling efficiency of light-emitting diodes (LEDs) emitting in the UV-C regime. Carbon impurities in the nitrogen sublattice (CN) of AlN are believed to be the origin of this absorption. A specially tailored experiment using a combination of ion implantation of boron, carbon, and neon with subsequent high-temperature annealing allows to separate the influence of intrinsic point defects and carbon impurities regarding this absorption. Herein, the presented results reveal the relevance of the intrinsic nitrogen-vacancy defect VN. This is in contradiction to the established explanation based on CN defects as the defect causing the 265 nm absorption and will be crucial for further UV-LED improvement. Finally, in this article, a new interpretation of the 265 nm absorption is introduced, which is corroborated by density functional theory (DFT) results from the past decade, which are reviewed and discussed based on the new findings

Defect induced changes on the excitation transfer dynamics in ZnS/Mn nanowires

Transients of Mn internal 3d5 luminescence in ZnS/Mn nanowires are strongly non-exponential. This non-exponential decay arises from an excitation transfer from the Mn ions to so-called killer centers, i.e., non-radiative defects in the nanostructures and is strongly related to the interplay of the characteristic length scales of the sample such as the spatial extensions, the distance between killer centers, and the distance between Mn ions. The transients of the Mn-related luminescence can be quantitatively described on the basis of a modified Förster model accounting for reduced dimensionality. Here, we confirm this modified Förster model by varying the number of killer centers systematically. Additional defects were introduced into the ZnS/Mn nanowire samples by irradiation with neon ions and by varying the Mn implantation or the annealing temperature. The temporal behavior of the internal Mn2+ (3d5) luminescence is recorded on a time scale covering almost four orders of magnitude. A correlation between defect concentration and decay behavior of the internal Mn2+ (3d5) luminescence is established and the energy transfer processes in the system of localized Mn ions and the killer centers within ZnS/Mn nanostructures is confirmed. If the excitation transfer between Mn ions and killer centers as well as migration effects between Mn ions are accounted for, and the correct effective dimensionality of the system is used in the model, one is able to describe the decay curves of ZnS/Mn nanostructures in the entire time window

Sputtering and redeposition of ion irradiated Au nanoparticle arrays : direct comparison of simulations to experiments

Ion beam processing of surfaces is well known to lead to sputtering, which conventionally is associated only with erosion of atoms from the material. We show here, by combination of experiments and a newly developed Monte Carlo algorithm, that in the case of nanoparticles in a regular two-dimensional array on surfaces, the redeposition of sputtered atoms may play a significant role on the system development. The simulations are directly compared to in situ experiments obtained using a dual focused Ga+ ion beam system and high resolution scanning electron microscopy, and explain the size evolution by a combination of sputtering and redeposition of sputtered material on neighboring particles. The effect is found to be dependent on the size of the nanoparticles: if the nanoparticle size is comparable to the ion range, the reposition is negligible. For larger nanoparticles the redeposition becomes significant and is able to compensate up to 20% of the sputtered material, effectively reducing the process of sputtering. The redeposition may even lead to significant growth: this was seen for the nanoparticles with the sizes much smaller than the ion range. Furthermore, the algorithm shows that significant redeposition is possible when the large size neighboring nanoparticles are present.Peer reviewe

Gate-controlled heat generation in ZnO nanowire FETs

Nanoscale heating production using nanowires has been shown to be particularly attractive for a number of applications including nanostructure growth, localized doping, transparent heating and sensing. However, all proof-of-concept devices proposed so far relied on the use of highly conductive nanomaterials, typically metals or highly doped semiconductors. In this article, we demonstrate a novel nanoheater architecture based on a single semiconductor nanowire field-effect transistor (NW-FET). Nominally undoped ZnO nanowires were incorporated into three-terminal devices whereby control of the nanowire temperature at a given source-drain bias was achieved by additional charge carriers capacitatively induced via the third gate electrode. Joule-heating selective ablation of poly(methyl methacrylate) deposited on ZnO nanowires was shown, demonstrating the ability of the proposed NW-FET configuration to enhance by more than one order of magnitude the temperature of a ZnO nanowire, compared to traditional two-terminal configurations. These findings demonstrate the potential of field-effect architectures to improve Joule heating power in nanowires, thus vastly expanding the range of suitable materials and applications for nanowire-based nanoheaters

Ion irradiation-induced sinking of Ag nanocubes into substrates

Ion irradiation can cause burrowing of nanoparticles in substrates, strongly depending on the material properties and irradiation parameters. In this study, we demonstrate that the sinking process can be accomplished with ion irradiation of cube-shaped Ag nanoparticles on top of silicon; how ion channeling affects the sinking rate; and underline the importance of the amorphous state of the substrate upon ion irradiation. Based on our experimental findings, the sinking process is described as being driven by capillary forces enabled by ion-induced plastic flow of the substrate.Comment: the manuscript has 25 pages and 6 figure