53 research outputs found
Improvement of current-control induced by oxide crenel in very short field-effect-transistor
A 2D quantum ballistic transport model based on the non-equilibrium Green's
function formalism has been used to theoretically investigate the effects
induced by an oxide crenel in a very short (7 nm) thin-film
metal-oxide-semiconductor-field-effect-transistor. Our investigation shows that
a well adjusted crenel permits an improvement of on-off current ratio Ion/Ioff
of about 244% with no detrimental change in the drive current Ion. This
remarkable result is explained by a nontrivial influence of crenel on
conduction band-structure in thin-film. Therefore a well optimized crenel seems
to be a good solution to have a much better control of short channel effects in
transistor where the transport has a strong quantum behavior
An electronic ratchet is required in nanostructured intermediate band solar cells
We investigate in this letter the intrinsic properties that have limited the
efficiency of nanostructured intermediate band solar cells. Those devices take
advantage of intra-band transitions, which occur on narrow energy width, and
present low radiative recombination efficiency. We derive the minimum
requirements in terms of those two characteristics to achieve efficiencies in
excess of the Shockley-Queisser limit, and show that compatible nanostructures
are challenging to obtain. Especially, we evidence that currently
experimentally considered materials cannot overcome the best single junction
cells. In order to solve those issues, we consider devices including an
electronic ratchet mechanism. Firstly, such devices are shown to be much less
sensitive on the limitations of the nanostructures characteristics, so that
requirements for high efficiencies can be met. Secondly, we show that quantum
well devices present advantages over their quantum dots counterparts, although
they have attracted much less interest so far
Coherent Phonons-Driven Hot Carrier Effect in a Superlattice Solar Cell
Carrier thermalization in a superlattice solar cell made of polar
semiconductors is studied theoretically by considering a minimal model where
electron-phonon scattering is the principal channel of carrier energy loss.
Importantly, the effect of an intrinsic quantum mechanical property; the phonon
coherence, on carrier thermalization is investigated, within semiclassical
picture in terms of phonon wave packet. It turns out that coherent longitudinal
optical (LO) phonons weaken the effective electron-phonon coupling, thus
supposedly lowering the carrier energy loss rate in solar cell. The resulting
thermalization power is indeed significantly reduced by the coherent phonons,
resulting in enhanced hot carrier effect, particularly for thin enough well
layer where carrier confinement is also strong. A recent experiment on
superlattice solar cell prototype is shown to manifest the coherent
phonons-driven phenomenon. Our results demonstrate the practical implications
of the fundamental quantum coherence property of phonons in semiconductors for
improving superlattice solar cell performance, via hot carrier effect.Comment: Accepted, to appear in Physical Review Applied (2023
Beneficial impact of a thin tunnel barrier in quantum well intermediate-band solar cell
Based on electronic quantum transport modeling, we study the transition between the intermediate-band and the conduction-band in nano-structured intermediate-band solar cell. We show that a tunnel barrier between the quantum well (QW) and the host material could improve the current. The confinement generated by such a barrier favors the inter-subband optical coupling in the QW and then changes the excitation-collection trade-off. More surprisingly, we also show that tunneling impacts the radiative recombination and then the voltage. Using a detailed balance model we explain and we propose a broadening factor for this Voc modification. Finally we show that a thin tunnel barrier is beneficial for both current and voltage
Flexible Photodiodes Based on Nitride Core/Shell p-n Junction Nanowires
International audienceA flexible nitride p-n photodiode is demonstrated. The device consists of a composite nanowire/polymer membrane trans- ferred onto a flexible substrate. The active element for light sensing is a vertical array of core/shell p−n junction nanowires containing InGaN/ GaN quantum wells grown by MOVPE. Electron/hole generation and transport in core/shell nanowires are modeled within nonequilibrium Green function formalism showing a good agreement with experimental results. Fully flexible transparent contacts based on a silver nanowire network are used for device fabrication, which allows bending the detector to a few millimeter curvature radius without damage. The detector shows a photoresponse at wavelengths shorter than 430 nm with a peak responsivity of 0.096 A/W at 370 nm under zero bias. The operation speed for a 0.3 × 0.3 cm2 detector patch was tested between 4 Hz and 2 kHz. The −3 dB cutoff was found to be ∼35 Hz, which is faster than the operation speed for typical photoconductive detectors and which is compatible with UV monitoring applications
A van der Waals heterojunction based on monolayers of MoS 2 and WSe 2 for overall solar water splitting
International audienceWe numerically investigated a complete system for overall water splitting based on TMDC heterojunctions. We found a solar-to-hydrogen efficiency higher than 15% under realistic operating conditions
ETUDE DU PHENOMENE D'IONISATION PAR CHOC DANS LES SEMI-CONDUCTEURS III-V (APPLICATION AUX TRANSISTORS A EFFET DE CHAMP)
ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF
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