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

Evaporative electron cooling in asymmetric double barrier semiconductor heterostructures

International audienceRapid progress in high-speed, densely packed electronic/photonic devices has brought unprecedented benefits to our society. However, this technology trend has in reverse led to a tremendous increase in heat dissipation, which degrades device performance and lifetimes. The scientific and technological challenge henceforth lies in efficient cooling of such high-performance devices. Here, we report on evaporative electron cooling in asymmetric Aluminum Gallium Arsenide/Gallium Arsenide (AlGaAs/GaAs) double barrier heterostructures. Electron temperature, T e , in the quantum well (QW) and that in the electrodes are determined from photoluminescence measurements. At 300 K, T e in the QW is gradually decreased down to 250 K as the bias voltage is increased up to the maximum resonant tunneling condition, whereas T e in the electrode remains unchanged. This behavior is explained in term of the evaporative cooling process and is quantitatively described by the quantum transport theory

Anharmonic phonon-phonon scattering at interface by non-equilibrium Green's function formalism

The understanding and modeling of inelastic scattering of thermal phonons at a solid/solid interface remain an open question. We present a fully quantum theoretical scheme to quantify the effect of anharmonic phonon-phonon scattering at an interface via non-equilibrium Green's function (NEGF) formalism. Based on the real-space scattering rate matrix, a decomposition of the interfacial spectral energy exchange is made into contributions from local and non-local anharmonic interactions, of which the former is shown to be predominant for high-frequency phonons whereas both are important for low-frequency phonons. The anharmonic decay of interfacial phonon modes is revealed to play a crucial role in bridging the bulk modes across the interface. The overall quantitative contribution of anharmonicity to thermal boundary conductance is found to be moderate. The present work promotes a deeper understanding of heat transport at the interface and an intuitive interpretation of anharmonic phonon NEGF formalism

Assessing Phonon Coherence Using Spectroscopy

As a fundamental physical quantity of thermal phonons, temporal coherence participates in a broad range of thermal and phononic processes, while a clear methodology for the measurement of phonon coherence is still lacking. In this Lettter, we derive a theoretical model for the experimental exploration of phonon coherence based on spectroscopy, which is then validated by comparison with Brillouin light scattering data and direct molecular dynamic simulations of confined modes in nanostructures. The proposed model highlights that confined modes exhibit a pronounced wavelike behavior characterized by a higher ratio of coherence time to lifetime. The dependence of phonon coherence on system size is also demonstrated from spectroscopy data. The proposed theory allows for reassessing data of conventional spectroscopy to yield coherence times, which are essential for the understanding and the estimation of phonon characteristics and heat transport in solids in general.Comment: 4 pages, 3 figure

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