3 research outputs found
Engineering Graphene Quantum Dots for Enhanced Ultraviolet and Visible Light p‑Si Nanowire-Based Photodetector
In
this work, a significant improvement of the classical silicon nanowire
(SiNW)-based photodetector was achieved through the realization of
core–shell structures using newly designed GQD<sup>PEI</sup>s via simple solution processing. The polyÂ(ethyleneimine) (PEI)-assisted
synthesis successfully tuned both optical and electrical properties
of graphene quantum dots (GQDs) to fulfill the requirements for strong
yellow photoluminescence emission along with large band gap formation
and the introduction of electronic states inside the band gap. The
fabrication of a GQD<sup>PEI</sup>-based device was followed by systematic
structural and photoelectronic investigation. Thus, the GQD<sup>PEI</sup>/SiNW photodetector exhibited a large photocurrent to dark current
ratio (<i>I</i><sub>ph</sub>/<i>I</i><sub>dark</sub> up to ∼0.9 × 10<sup>2</sup> under 4 V bias) and a remarkable
improvement of the external quantum efficiency values that far exceed
100%. In this frame, GQD<sup>PEI</sup>s demonstrate the ability to
arbitrate both charge-carrier photogeneration and transport inside
a heterojunction, leading to simultaneous attendance of various mechanisms:
(i) efficient suppression of the dark current governed by the type
I alignment in energy levels, (ii) charge photomultiplication determined
by the presence of the PEI-induced electron trap levels, and (iii)
broadband ultraviolet-to-visible downconversion effects
Electron Accumulation Tuning by Surface-to-Volume Scaling of Nanostructured InN Grown on GaN(001) for Narrow-Bandgap Optoelectronics
The existence of an uncontrolled electron accumulation
layer near
the surface of InN thin films is an obstacle for the development of
reliable InN-based devices for use in narrow-bandgap optoelectronics.
In this article, we show that this can be regulated by modulating
the surface of the InN grown on GaN(001). By increasing the surface-to-volume
ratio, we can demonstrate a reduction in the surface carrier concentration
from ∼1018 to ∼1017 cm–3. These controlled changes are despite the idea that donor-type surface
states, which contribute to conduction band electrons are reported
to be the main origin of the surface charge density. Additionally,
by evaluating the surface carrier concentration through modeling of
photoluminescence (PL) spectroscopy, we have found a failure of the
Burstein–Moss theory. Conversely, modeling of the longitudinal
optical phonon–plasmon coupled modes measured using Raman spectroscopy,
simulations of InN structures using the k·p method, and Hall effect measurements, where possible,
showed an excellent correlation of the surface electron concentrations.
The large inhomogeneous broadening in the PL, which overwhelms any
broadening due to the Burstein–Moss effect, is understood to
be the result of varying Stark shifts due to varying strain throughout
high surface-to-volume nanostructures, which dramatically affects
the spatially indirect nature of the electron–hole recombination.
Finally, our findings demonstrate how the electron population of 2D
and 3D InN nanostructures can be tuned by structural features, such
as porosity and/or the surface-to-volume ratio
Electron Accumulation Tuning by Surface-to-Volume Scaling of Nanostructured InN Grown on GaN(001) for Narrow-Bandgap Optoelectronics
The existence of an uncontrolled electron accumulation
layer near
the surface of InN thin films is an obstacle for the development of
reliable InN-based devices for use in narrow-bandgap optoelectronics.
In this article, we show that this can be regulated by modulating
the surface of the InN grown on GaN(001). By increasing the surface-to-volume
ratio, we can demonstrate a reduction in the surface carrier concentration
from ∼1018 to ∼1017 cm–3. These controlled changes are despite the idea that donor-type surface
states, which contribute to conduction band electrons are reported
to be the main origin of the surface charge density. Additionally,
by evaluating the surface carrier concentration through modeling of
photoluminescence (PL) spectroscopy, we have found a failure of the
Burstein–Moss theory. Conversely, modeling of the longitudinal
optical phonon–plasmon coupled modes measured using Raman spectroscopy,
simulations of InN structures using the k·p method, and Hall effect measurements, where possible,
showed an excellent correlation of the surface electron concentrations.
The large inhomogeneous broadening in the PL, which overwhelms any
broadening due to the Burstein–Moss effect, is understood to
be the result of varying Stark shifts due to varying strain throughout
high surface-to-volume nanostructures, which dramatically affects
the spatially indirect nature of the electron–hole recombination.
Finally, our findings demonstrate how the electron population of 2D
and 3D InN nanostructures can be tuned by structural features, such
as porosity and/or the surface-to-volume ratio