Zn2GeO4 is a novel transparent conductive oxide material, with an ultra-wide band gap of 4.5 eV, and rather good electrical conductivity. Zn2GeO4 nano- and microwires grown by a thermal technique show two intense emission bands centered in the UV and VIS region, respectively. In this work, we have studied the correlation between luminescence and structural properties in undoped and Mg doped samples. The waveguiding behavior of the microrods has been assessed by the excitation with a 325 nm laser and analysis of the transmitted light along the structure. The intense white luminescence of Zn2GeO4 nanomaterials makes them of interest as efficient phosphors for field emission displays.
On one hand, interest on the tunability of the optical microcavities has increased in the last few years due to the need for selective nano- and microscale light sources to be used as photonic building blocks in several applications. On the other, transparent conductive oxide (TCO) β-Ga2O3 is attracting attention in the optoelectronics area due to its ultra wide band gap and high breakdown field. However, at the micro- and nanoscale there are still some challenges to face up, namely the control and tuning of the optical and electrical properties of this oxide. In this work, Cr doped Ga2O3 elongated microwires are grown using the vapor-solid (VS) mechanism. Focused Ion Beam (FIB) etching forms Distributed Bragg Reflector (DBR)-based resonant microcavities. Room temperature microphotoluminescence (μ-PL) spectra show strong modulations in the red-NIR range on five cavities with different lengths. Selectivity of the peak wavelengths is obtained, proving the tunability of this kind of optical systems. The confined modes are analyzed experimentally, analytically and via finite difference time domain (FDTD) simulations. Experimental reflectivities up to 78% are observed.
The synthesis of complex nanostructures that combine materials and dimensionality, promises the ability to identify novel designs and architectures with enhanced properties that could be used in new devices. One of the building blocks in nanomaterials are nanowires, which offer several possibilities to get complex nanostructures. We present two kinds of morphologies based on oxide nanowires obtained by a thermal evaporation method. The common feature of both morphologies is a central oxide nanowire and, depending on the growth parameters, nanowires with either nanocrystallites or nano/microrods attached to the central wire are obtained. We have previously reported the fabrication of several single oxide nanowires and in particular, gallium oxide (β-Ga2O3) and zinc germanate oxide (Zn2GeO4) nanowires. Here we report the shape evolution of these nanowires by the suitable modification of the growth parameters. The addition of tin oxide (SnO2) to the precursors and variation of the thermal treatments duration result in the formation of the above-mentioned complex nanostructures. Structural and chemical characterizations were performed by electron microscopy techniques and Raman spectroscopy. The results shed light on the understanding of the driving mechanisms that lead to the formation of complex oxide nanostructures.
Ga2O3 bulk single crystals have been implanted with 300 keV Europium ions to fluences ranging from 1×1013 to 4×1015 at/cm2. The damage build-up and Eu-incorporation was assessed by Rutherford Backscattering Spectrometry in the channeling mode (RBS/C). RBS/C results suggest that implantation causes a mixture of defect clusters and extended defects such as dislocations. Amorphisation starts at the surface for fluences around 1×1015 at/cm2 and then proceeds to deeper regions of the sample with increasing fluence. Amorphous regions and defect clusters are efficiently removed during rapid thermal annealing at ~1100 °C; however, Eu diffuses towards the surface. Nevertheless, Eu ions are optically activated and show cathodoluminescence at room temperature. Results in bulk samples are compared to those in Eu-implanted Ga2O3 nanowires and despite strong similarities in the structural properties differences were found in the optical activation. Furthermore, damage and dopant incorporation studies were performed using the Perturbed Angular Correlation technique, which allows probing the immediate lattice surroundings of an implanted radioactive probe at the atomic level.
Interest on the control of light at the nano- and microscale has increased in the last years because of the incorporation of nanostructures into optical devices. In particular, semiconductor oxides microstructures emerge as important active materials for waveguiding and confinement of light from UV to NIR wavelengths. The fabrication of high quality and quantity of nano- and microstructures of semiconductor oxides with controllable morphology and tunable optical properties is an attractive challenge in this field. In this work, waveguiding and optical confinement applications of different micro- and nanostructures of gallium oxide and antimony oxide have been investigated. Structures with morphologies such as nanowires, nanorods or branched nanowires as elongated structures, but also triangles, microplates or pyramids have been obtained by a thermal evaporation method. Light waveguide experiments were performed with both oxides, which have wide band gap and a rather high refractive index. The synthesized microstructures have been found to act as optical cavities and resonant modes were observed. In particular, photoluminescence results showed the presence of resonant peaks in the PL spectra of Ga2O3 microwires and Sb2O3 micro-triangles and rods, which suggest their applications as optical resonators in the visible range.
Monoclinic gallium oxide, β-Ga2O3, is a transparent conducting oxide (TCO) that presents one of the widest band gaps
among this family of materials. Its characteristics make it highly interesting for applications in UV - visible - IR
optoelectronic and photonic devices. On the other hand, the morphology of nanowires made of this oxide presents
specific advantages for light emitting nanodevices, waveguides and gas sensors. Control of doping of the nanostructures
is of the utmost importance in order to tailor the behavior of these devices.
In this work, the growth of the nanowires is based on the vapor-solid (VS) mechanism during thermal annealing
treatment while the doping process was carried out in three different ways. In one of the cases, doping was obtained
during the growth of the wires. A second method was based on thermal diffusion of the dopants after the growth of
undoped nanowires, while the third method used ion implantation to introduce optically active ions into previously
grown nanowires. The study of the influence of the different dopants on the luminescence properties of gallium oxide
nanowires is presented. In particular, transition metals and rare earths such as Cr, Gd, Er or Eu were used as optically
active dopants that allowed selection of the luminescence wavelength, spanning from the UV to the IR ranges. The
benefits and drawbacks of the three different doping methods are analyzed. The waveguiding behavior of the doped
nanowires has been studied by room temperature micro-photoluminescence.