K. Leifer

Focused electron beam induced deposition of gold

Codeposition of hydrocarbons is a severe problem during focused electron beam writing of pure metal nanostructures. When using organometallic precursors, a low metal content carbonaceous matrix embedding and separating numerous nanosized metal clusters is formed. In this work, we present a new and easy approach to obtain high purity gold lines: the use of inorganic PF3AuCl as a precursor. Electrical resistivities as low as 22 µOhms cm at 295 K (ten times the bulk Au value) were obtained. This is to our knowledge the best value for focused electron beam deposition obtained from the vapor phase so far. No special care was taken to prevent hydrocarbon contamination. The deposited nanostructure consists of gold grains varying in size and percolation with beam parameters.

Structure and optical properties of semiconductor quantum nanostructures self-formed in inverted tetrahedral pyramids

We present a method for fabricating quantum dots using seeded self-organized growth of GaAs/AlGaAs heterostructures on substrates patterned with inverted pyramids. This method produces, at the tip of each inverted pyramid, highly uniform quantum dots whose size and position can be accurately controlled. In addition, a system of connected GaAs and AlGaAs two- and one-dimensional nanostructures is identified in the inverted pyramids using cross-sectional atomic force microscopy. A substrate removal technique is used to optimally prepare our samples for optical studies, allowing the increase of the luminescence efficiency of the quantum dots by up to three orders of magnitude. Micro-photoluminescence and cathodo-luminescence spectroscopy are used to study in detail the bandgap structure of the connected nanostructures identified in the pyramids, which constitute a complex, but controlled, barrier environment for the quantum dots.

Dense uniform arrays of site-controlled quantum dots grown in inverted pyramids

We report on the growth and optical properties of homogeneous, dense arrays of site-controlled, single GaAs/AlGaAs quantum dot (QD) heterostructures with periodicities as small as 300 nm. The samples were grown by organometallic chemical vapor deposition on (111)B GaAs substrates containing dense inverted pyramid recess patterns prepared by electron beam lithography and wet chemical etching. Low-temperature microphotoluminescence spectra of the samples show distinct luminescence from the QDs with 1–3 meV linewidth. Low-temperature cathodoluminescence spectrally resolved images reveal uniform emission energy within an ensemble of 900 QDs.

Electron beam induced deposition of metallic tips and wires for microelectronics applications

Resistivity measurements and composition analysis of electron beam induced deposition (EBID) with two novel inorganic carbon-free precursors [RhCl(PF3)2]2 (CAS 14876-98-3) and AuCl(PF3) (CAS 141845-34-3) are compared with results obtained from metallorganic CVD precursors Me2?Au-tfa (CAS 63470-53-1) and Me2?Au-hfa (CAS 63470-54-2). A deposit/metal resistivity ratio of 10 was obtained for EBID with AuCl(PF3).

Structure and Photoluminescence of Single AlGaAs/GaAs Quantum Dots Grown in Inverted Tetrahedral Pyramids

Arrays of single GaAs/AlGaAs quantum dot (QD) heterostructures grown by organometallic chemical vapor deposition in inverted tetrahedral pyramids on {111}B GaAs substrates are investigated. Cross-sectional atomic force microscopy images evidence a pronounced thickening of the GaAs quantum well layer at the tip of the pyramid, giving rise to a lens-like QD structure. Low-temperature photoluminescence and cathodoluminescence spectra show distinct luminescence from the dots, exhibiting filling of QD states separated by 33 meV at increased carrier densities. Luminescence linewidths of 15 meV and line energy variations of less than 5 meV are obtained across mm2 sample areas.

Influence of strain and quantum confinement on the optical properties of InGaAs/GaAs V-groove quantum wires

We report on the impact of quantum confinement and strain effects on the optical properties of state-of-the-art, densely stacked, In0.15Ga0.85As/GaAs V-groove quantum wires. High uniformity and efficient carrier capture lead to narrow (6 meV) and intense emission from the wires. Large optical polarization anisotropy is obtained thanks to the combined effects of lateral quantum confinement and triaxial strain. Band filling in the fundamental subband occurs at a modest carrier density (∼9×105u200acm−1), and is accompanied by a small spectral blueshift of the emission. Several sharp excitonic resonances associated with two dimensionally confined subbands of dominant heavy-hole character are observed in photoluminescence excitation spectroscopy, together with a remarkably small Stokes shift (3 meV). The subband separations (∼24 meV) are nearly independent of the wire thickness, as the nonuniform Indium composition across the structure is found to dominate the lateral confinement for thick wires. Such strained qua...

Carrier transport and luminescence in inverted-pyramid quantum structures

Cathodoluminescence spectroscopy and wavelength-dispersive imaging were employed for investigating the carrier transport and recombination in GaAs/AlGaAs inverted-pyramid quantum dot (QD) heterostructures grown on patterned (111)B GaAs substrates. The spectra and images clearly evidence carrier recombination in quantum wells and quantum wires (QWR) and show potential variations in these structures. Luminescence from the lens-shaped QDs was identified and characterized as a function of the GaAs layer thickness. Furthermore, we show a tapering of the GaAs QWR that self-forms at the corners of the pyramids. Application of such tapered QWRs as “exciton accelerators” is discussed.

Effect of indium segregation on optical properties of V-groove InGaAs/GaAs strained quantum wires

Self-ordered, strained InGaAs/GaAs quantum structures are grown on V-grooved GaAs substrates. The lateral patterning of these nonplanar heterostructures allows the growth of defect-free strained structures with thickness exceeding that achieved with planar epitaxy. Indium segregation at the bottom of the groove results in the formation of a vertical InGaAs quantum-well structure with In-enriched composition. We studied in detail the influence of nominal thickness and In content on the photoluminescence peak energy of these quantum wires. Room-temperature emission at 1.16 μm with a relatively narrow linewidth (30–35 meV) is achieved as a demonstration of the potential of this approach for fabricating long-wavelength semiconductor light sources on GaAs substrates.

Experimental method for high-accuracy reflectivity-spectrum measurements

An experimental method for accurate measurements of the reflectivity spectrum of mirrors is presented. It combines the noise reduction obtained with multiple beam reflections on two identical mirrors; high-beam quality, owing to the use of single-mode optical fibers; and high immunity against intensity variations of the beam. This method is demonstrated for characterizing a 30-period GaAs/Al(0.65)Ga(0.35)As distributed Bragg reflector designed for long-wavelength vertical-cavity surface-emitting lasers. Its peak reflectivity is found to be 99.43 ? 0.04% at 1.562 mum, and an optical absorption coefficient of alpha = 36 ? 6 cm(-1) is derived. The peak internal reflectivity of this distributed Bragg reflector used as the top mirror in a wafer-fused vertical-cavity surface-emitting laser is calculated to be 98.87 ? 0.12%, and the transmission is 0.28%.

Focused electron beam induced deposition of gold and rhodium

Keywords: [NRG] Reference LOA-CONF-2000-010 URL: AtlantisMADMAD publicPubli Present ConferencesPublicationsprinted papers2000 : NRG Hoffmann MRSP 2000 37 Record created on 2009-07-20, modified on 2017-05-10