Understanding Polarization Properties of InAs Quantum Dots by Atomistic Modeling of Growth Dynamics

A model for realistic InAs quantum dot composition profile is proposed and analyzed, consisting of a double region scheme with an In-rich internal core and an In-poor external shell, in order to mimic the atomic scale phenomena such as In-Ga intermixing and In segregation during the growth and overgrowth with GaAs. The parameters of the proposed model are derived by reproducing the experimentally measured polarization data. Further understanding is developed by analyzing the strain fields which suggests that the two-composition model indeed results in lower strain energies than the commonly applied uniform composition model.Comment: in press, AIP proceedings for ICPS 2012 - 31st International Conference on the Physics of Semiconductors, July 29-August 3, 2012 Zuric

Multicolored devices fabricated by direct lithography of colloidal nanocrystals

Colloidal nanocrystals (NCs) are interesting as potential active medium for novel nanophotonic and nanoelectronic devices, due to their low fabrication costs and full tunability of their opto-electronic properties. In this work we report a multi step approach for the fabrication of multicolored micro- and nano- displays by localizing NCs through lithographic techniques without recurring to etching processes or surface treatment of the substrate. We demonstrate the possibility to localize different ensembles of emitters on the same substrate by realigned photolithographic steps or mix-and-match electron beam and photolithographic approaches. Moreover, fine tuning of the overall pixel emission is shown by varying the concentration ratio among localized red and green NCs. This technique enables the fabrication of optically pumped colored pixels with very high definition. Our approach combined with advances in NCs-based light emitting diodes technology will enable the electrical injection of advanced micro and nano light sources

Novel Time-Domain Circuit Modelling of χ(2) Nonlinear Process in Periodic Optical Waveguide

In this work we present a new time domain modelling approach of χ (2) nonlinear processes in periodic slab waveguides and cavities. This method exploits the Hertzian Potential Modelling (HPM) to design discontinuous dielectric interfaces. It is based on a circuital approach which considers the time-domain nonlinear wave propagation in transmission lines coupled with voltage and current generators. These generators are placed directly on the interface nodes thus optimizing the numerical error of the temporal second derivatives at the dielectric boundaries, and providing an accurate characterization of the nonlinear processes in integrated optics

Scalar time domain modeling and coupling of second harmonic generation process in GaAs discontinuous optical waveguide

We present in this work the scalar potential formulation of second harmonic generation process in chi((2)) nonlinear analysis. This approach is intrinsically well suited to the applications of the concept of circuit analysis and synthesis to nonlinear optical problems, and represents a novel alternative method in the analysis of nonlinear optical waveguide, by providing a good convergent numerical solution. The time domain modeling is applied to nonlinear GaAs asymmetrical waveguide with dielectric discontinuities in the hypothesis of quasi phase matching condition in order to evaluate the efficiency conversion of the second harmonic signal. The accuracy of the modeling is validated by the good agreement with the published experimental results. The effective dielectric constant method allows to extend the analysis also to 3D optical waveguides. (c) 2008 Optical Society of America

Design of nonlinear GaAs/AlGaAs second harmonic converters

Abstract In this work we present the design of a three-dimensional wavelength converter consisting of GaAs/AlGaAs nonlinear ridge waveguide with a quasi-phase-matched grating. A fundamental mode at λ FU = 1.55 μ m , and a copropagating second harmonic mode at λ SH = 0.775 μ m are considered. The second harmonic generation process in the χ ( 2 ) nonlinear waveguides is analysed by analytical and numerical approaches. The numerical approach is performed by the Hertzian potential formulation typically used for the modelling of χ ( 2 ) nonlinear processes. A good agreement between analytical and numerical results is observed

Stress-driven AlN cantilever-based flow sensor for fish lateral line system

In this work, we report on the fabrication and characterization of stress-driven aluminum nitride (AlN) cantilevers to be applied as flow sensor for fish lateral line system. The fabricated structures exploit a multilayered cantilever AlN/molybdenum (Mo) and a Nichrome 80/20 alloy as piezoresistor. Cantilever arrays are realized by using conventional micromachining techniques involving optical lithography and etching processes. The fabrication of the piezoresistive cantilevers is reported and the operation of the cantilever as flow sensor has been investigated by electrical measurement under nitrogen flowing condition showing a sensitivity to directionality and to low value applied forces

Polarization Response in InAs Quantum Dots: Theoretical Correlation between Composition and Electronic Properties

III-V growth and surface conditions strongly influence the physical structure and resulting optical properties of self-assembled quantum dots (QDs). Beyond the design of a desired active optical wavelength, the polarization response of QDs is of particular interest for optical communications and quantum information science. Previous theoretical studies based on a pure InAs QD model failed to reproduce experimentally observed polarization properties. In this work, multi-million atom simulations are performed to understand the correlation between chemical composition and polarization properties of QDs. A systematic analysis of QD structural parameters leads us to propose a two layer composition model, mimicking In segregation and In-Ga intermixing effects. This model, consistent with mostly accepted compositional findings, allows to accurately fit the experimental PL spectra. The detailed study of QD morphology parameters presented here serves as a tool for using growth dynamics to engineer the strain field inside and around the QD structures, allowing tuning of the polarization response.Comment: 8 pages, 6 figures; accepted for publication in IOP Nanotechnology journa

A fully integrated GaAs-based three-axis Hall magnetic sensor exploiting self-positioned strain released structures

In this work, we demonstrate a fully integrated three-axis Hall magnetic sensor by exploiting microfabrication technologies applied to a GaAs-based heterostructure. This allows us to obtain, by the same process, three mutually orthogonal sensors: an in-plane Hall sensor and two out-of-plane Hall sensors. The micromachined devices consist of a two-dimensional electron gas AlGaAs/InGaAs/GaAs multilayer which represents the sensing structure, grown on the top of an InGaAs/GaAs strained bilayer. After the release from the substrate, the strained bilayer acts as a hinge for the multilayered structure allowing the out-of-plane self-positioning of devices. Both the in-plane and out-of-plane Hall sensors show a linear response versus the magnetic field with a sensitivity for current-biased devices higher than 1000 V A−1 T−1, corresponding to an absolute sensitivity more than 0.05 V T−1 at 50 µA. Moreover, Hall voltage measurements, as a function of the mechanical angle for both in-plane and out-of-plane sensors, demonstrate the potential of such a device for measurements of the three vector components of a magnetic field

Design and modeling of χ(2) second harmonic amplification in circular photonic crystal

We analyze in this work the second harmonic amplification of χ(2) nonlinear process in membrane type GaAs circular photonic crystal. This unconventional kind of photonic crystal is well suited for the generation of whispering gallery modes due to the circular symmetric periodic pattern. The Gaussian beam of a fundamental pump signal at 1.55 μm defines a whispering gallery mode resonance and generates a second harmonic mode at 0.775 μm in the central missing hole micro-cavity. The periodic pattern and the micro-cavity are tailored and optimized in order to generate a second harmonic conversion efficiency of 50 %. We predict the resonances by an accurate 2D time domain model including χ(2) nonlinearity and also by a 3D Finite Element Method FEM. Moreover, by using a 3D membrane configuration, we predict a quality factor of the second harmonic mode of the order of 35000