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