44 research outputs found
In vacancies in InN grown by plasma-assisted molecular beam epitaxy
The authors have applied positron annihilation spectroscopy to study the
effect of different growth conditions on vacancy formation in In- and N-polar
InN grown by plasma-assisted molecular beam epitaxy. The results suggest that
the structural quality of the material and limited diffusion of surface adatoms
during growth dictate the In vacancy formation in low electron-density undoped
epitaxial InN, while growth conditions and thermodynamics have a less important
role, contrary to what is observed in, e.g., GaN. Further, the results imply
that in high quality InN, the electron mobility is likely limited not by
ionized point defect scattering, but rather by threading dislocations.Comment: 15 pages, 2 figure
Self-induced ultrafast electron-hole plasma temperature oscillations in nanowire lasers
Nanowire lasers can be monolithically and site-selectively integrated onto
silicon photonic circuits. To assess their full potential for ultrafast
opto-electronic devices, a detailed understanding of their lasing dynamics is
crucial. However, the roles played by their resonator geometry and the
microscopic processes that mediate energy exchange between the photonic,
electronic, and phononic subsystems are largely unexplored. Here, we study the
dynamics of GaAs-AlGaAs core-shell nanowire lasers at cryogenic temperatures
using a combined experimental and theoretical approach. Our results indicate
that these NW lasers exhibit sustained intensity oscillations with frequencies
ranging from 160 GHz to 260 GHz. As the underlying physical mechanism, we
identified self-induced electron-hole plasma temperature oscillations resulting
from a dynamic competition between photoinduced carrier heating and cooling via
phonon scattering. These dynamics are intimately linked to the strong
interaction between the lasing mode and the gain material, which arises from
the wavelength-scale dimensions of these lasers. We anticipate that our results
could lead to new approaches for ultrafast intensity and phase modulation of
chip-integrated nanoscale semiconductor lasers.Comment: Revised manuscrip
Self-induced ultrafast electron-hole-plasma temperature oscillations in nanowire lasers
Nanowire lasers can be monolithically and site-selectively integrated onto silicon photonic circuits. To assess their full potential for ultrafast optoelectronic devices, a detailed understanding of their lasing dynamics is crucial. However, the roles played by their resonator geometry and the microscopic processes that mediate energy exchange between the photonic, electronic, and phononic subsystems are largely unexplored. Here, we study the dynamics of GaAs-AlGaAs core-shell nanowire lasers at cryogenic tem- peratures using a combined experimental and theoretical approach. Our results indicate that these NW lasers exhibit sustained intensity oscillations with frequencies ranging from 160 GHz to 260 GHz. As the underlying physical mechanism, we have identified self-induced electron-hole plasma temperature oscilla- tions resulting from a dynamic competition between photoinduced carrier heating and cooling via phonon scattering. These dynamics are intimately linked to the strong interaction between the lasing mode and the gain material, which arises from the wavelength-scale dimensions of these lasers. We anticipate that our results could lead to optimised approaches for ultrafast intensity and phase modulation of chip-integrated semiconductor lasers at the nanoscale
In-polar InN grown by plasma-assisted molecular beam epitaxy
We study the effect of different deposition conditions on the properties of In-polar InN grown by plasma-assisted molecular beam epitaxy. GaN buffer layers grown in the Ga-droplet regime prior to the InN deposition significantly improved the surface morphology of InN films grown with excess In flux. Using this approach, In-polar InN films have been realized with room temperature electron mobilities as high as 2250 cm(2)/V s. We correlate electron concentrations in our InN films with the unintentionally incorporated impurities, oxygen and hydrogen. A surface electron accumulation layer of 5.11x10(13) cm(-2) is measured for In-polar InN. Analysis of optical absorption data provides a band gap energy of similar to 0.65 eV for the thickest InN films. (c) 2006 American Institute of Physics
Dynamic Acoustic Control of Individual Optically Active Quantum Dot-like Emission Centers in Heterostructure Nanowires
We probe and control the optical properties of emission centers forming in
radial het- erostructure GaAs-Al0.3Ga0.7As nanowires and show that these
emitters, located in Al0.3Ga0.7As layers, can exhibit quantum-dot like
characteristics. We employ a radio frequency surface acoustic wave to
dynamically control their emission energy and occupancy state on a nanosec- ond
timescale. In the spectral oscillations we identify unambiguous signatures
arising from both the mechanical and electrical component of the surface
acoustic wave. In addition, differ- ent emission lines of a single quantum dot
exhibit pronounced anti-correlated intensity oscilla- tions during the acoustic
cycle. These arise from a dynamically triggered carrier extraction out of the
quantum dot to a continuum in the radial heterostructure. Using finite element
modeling and Wentzel-Kramers-Brillouin theory we identify quantum tunneling as
the underlying mech- anism. These simulation results quantitatively reproduce
the observed switching and show that in our systems these quantum dots are
spatially separated from the continuum by > 10.5 nm.Comment: This document is the unedited Author's version of a Submitted Work
that was subsequently accepted for publication in Nano Letters, copyright
\c{copyright} American Chemical Society after peer review. To access the
final edited and published work see
http://pubs.acs.org/doi/abs/10.1021/nl404043