Ordered arrays of embedded Ga nanoparticles on patterned silicon substrates

Submicron-Size Emitters of the 1.2-1.55 μm Spectral Range Based on InP/InAsP/InP Nanostructures Integrated into Si Substrate

We study photoluminescence of InP/InAsP/InP nanostructures monolithically integrated to a Si(100) substrate. The InP/InAsP/InP nanostructures were grown in pre-formed pits in the silicon substrate using an original approach based on selective area growth and driven by a molten alloy in metal-organic vapor epitaxy method. This approach provides the selective-area synthesis of the ordered emitters arrays on Si substrates. The obtained InP/InAsP/InP nanostructures have a submicron size. The individual InP/InAsP/InP nanostructures were investigated by photoluminescence spectroscopy at room temperature. The tuning of the emission line in the spectral range from 1200 nm to 1550 nm was obtained depending on the growth parameters. These results provide a path for the growth on Si(100) substrate of position-controlled heterojunctions based on InAs_1-xP_x for nanoscale optical devices operating at the telecom band.

Monolithic integration of InP on Si by molten alloy driven selective area epitaxial growth

We report a new approach for monolithic integration of III-V materials into silicon, based on selective area growth and driven by a molten alloy in metal-organic vapor epitaxy. Our method includes elements of both selective area and droplet-mediated growths and combines the advantages of the two techniques. Using this approach, we obtain organized arrays of high crystalline quality InP insertions into (100) oriented Si substrates. Our detailed structural, morphological and optical studies reveal the conditions leading to defect formation. These conditions are then eliminated to optimize the process for obtaining dislocation-free InP nanostructures grown directly on Si and buried below the top surface. The PL signal from these structures exhibits a narrow peak at the InP bandgap energy. The fundamental aspects of the growth are studied by modeling the InP nucleation process. The model is fitted by our X-ray diffraction measurements and correlates well with the results of our transmission electron microscopy and optical investigations. Our method constitutes a new approach for the monolithic integration of active III-V materials into Si platforms and opens up new opportunities in active Si photonics.

Selective Area Epitaxy of GaAs/Ge/Si Nanomembranes: A Morphological Study

We demonstrate the feasibility of growing GaAs nanomembranes on a plastically-relaxed Ge layer deposited on Si (111) by exploiting selective area epitaxy in MBE. Our results are compared to the case of the GaAs homoepitaxy to highlight the criticalities arising by switching to heteroepitaxy. We found that the nanomembranes evolution strongly depends on the chosen growth parameters as well as mask pattern. The selectivity of III-V material with respect to the SiO2 mask can be obtained when the lifetime of Ga adatoms on SiO2 is reduced, so that the diffusion length of adsorbed Ga is high enough to drive the Ga adatoms towards the etched slits. The best condition for a heteroepitaxial selective area epitaxy is obtained using a growth rate equal to 0.3 ML/s of GaAs, with a As BEP pressure of about 2.5 × 10−6 torr and a temperature of 600 °C.

Droplet epitaxy of semiconductor nanostructures for quantum photonic devices

The long dreamed 'quantum internet' would consist of a network of quantum nodes (solid-state or atomic systems) linked by flying qubits, naturally based on photons, travelling over long distances at the speed of light, with negligible decoherence. A key component is a light source, able to provide single or entangled photon pairs. Among the different platforms, semiconductor quantum dots (QDs) are very attractive, as they can be integrated with other photonic and electronic components in miniaturized chips. In the early 1990s two approaches were developed to synthetize self-assembled epitaxial semiconductor QDs, or 'artificial atoms'-namely, the Stranski-Krastanov (SK) and the droplet epitaxy (DE) methods. Because of its robustness and simplicity, the SK method became the workhorse to achieve several breakthroughs in both fundamental and technological areas. The need for specific emission wavelengths or structural and optical properties has nevertheless motivated further research on the DE method and its more recent development, local droplet etching (LDE), as complementary routes to obtain high-quality semiconductor nanostructures. The recent reports on the generation of highly entangled photon pairs, combined with good photon indistinguishability, suggest that DE and LDE QDs may complement (and sometimes even outperform) conventional SK InGaAs QDs as quantum emitters. We present here a critical survey of the state of the art of DE and LDE, highlighting the advantages and weaknesses, the achievements and challenges that are still open, in view of applications in quantum communication and technology.

Ga metal nanoparticle-GaAs quantum molecule complexes for terahertz generation

A hybrid metal-semiconductor nanosystem for the generation of THz radiation, based on the fabrication of GaAs quantum molecules-Ga metal nanoparticles complexes through a self assembly approach, is proposed. The role of the growth parameters, the substrate temperature, the Ga and As flux during the quantum dot molecule (QDM) fabrication and the metal nanoparticle alignment are discussed. The tuning of the relative positioning of QDMs and metal nanoparticles is obtained through the careful control of Ga droplet nucleation sites via Ga surface diffusion. The electronic structure of a typical QDM was evaluated on the base of the morphological characterizations performed by atomic force microscopy and cross sectional scanning electron microscopy, and the predicted results confirmed by micro-photoluminescence experiments, showing that the Ga metal nanoparticle-GaAs quantum molecule complexes are suitable for terahertz generation from intraband transition.

Tunable plasmonic resonance of gallium nanoparticles by thermal oxidation at low temperaturas

The effect of the oxidation of gallium nanoparticles (Ga NPs) on their plasmonic properties is investigated. Discrete dipole approximation has been used to study the wavelength of the out-of-plane localized surface plasmon resonance in hemispherical Ga NPs, deposited on silicon substrates, with oxide shell (Ga₂O₃) of different thickness. Thermal oxidation treatments, varying temperature and time, were carried out in order to increase experimentally the Ga₂O₃ shell thickness in the NPs. The optical, structural and chemical properties of the oxidized NPs have been studied by spectroscopic ellipsometry, scanning electron microscopy, grazing incidence x-ray diffraction and x-ray photoelectron spectroscopy. A clear redshift of the peak wavelength is observed, barely affecting the intensity of the plasmon resonance. A controllable increase of the Ga₂O₃ thickness as a consequence of the thermal annealing is achieved. In addition, simulations together with ellipsometry results have been used to determine the oxidation rate, whose kinetics is governed by a logarithmic dependence. These results support the tunable properties of the plasmon resonance wavelength in Ga NPs by thermal oxidation at low temperatures without significant reduction of the plasmon resonance intensity.

Nucleation of Ga droplets on Si and SiOx surfaces

We report on gallium droplet nucleation on silicon (100) substrates with and without the presence of the native oxide. The gallium deposition is carried out under ultra-high vacuum conditions at temperatures between 580 and 630 °C. The total droplet volume, obtained from a fit to the diameter-density relation, is used for sample analysis on clean silicon surfaces. Through a variation of the 2D equivalent Ga thickness, the droplet diameter was found to be between 250-1000 nm. Longer annealing times resulted in a decrease of the total droplet volume. Substrate temperatures of 630 °C and above led to Ga etching into the Si substrates and caused Si precipitation around the droplets. In contrast, we obtained an almost constant diameter distribution around 75 nm over a density range of more than two orders of magnitude in the presence of a native oxide layer. Furthermore, the droplet nucleation was found to correlate with the density of surface features on the 'epi-ready' wafer.