scholarly journals Ab initio study of hot electrons in GaAs

2015 ◽  
Vol 112 (17) ◽  
pp. 5291-5296 ◽  
Author(s):  
Marco Bernardi ◽  
Derek Vigil-Fowler ◽  
Chin Shen Ong ◽  
Jeffrey B. Neaton ◽  
Steven G. Louie
Keyword(s):  
Ab Initio ◽  
Phonon Scattering ◽  
Carrier Dynamics ◽  
Hot Electrons ◽  
Hot Electron ◽  
Hot Carriers ◽  
Hot Carrier ◽  
Acoustic Modes ◽  
Decay Times ◽  
Electron Phonon Scattering

Hot carrier dynamics critically impacts the performance of electronic, optoelectronic, photovoltaic, and plasmonic devices. Hot carriers lose energy over nanometer lengths and picosecond timescales and thus are challenging to study experimentally, whereas calculations of hot carrier dynamics are cumbersome and dominated by empirical approaches. In this work, we present ab initio calculations of hot electrons in gallium arsenide (GaAs) using density functional theory and many-body perturbation theory. Our computed electron–phonon relaxation times at the onset of the Γ, L, and X valleys are in excellent agreement with ultrafast optical experiments and show that the ultrafast (tens of femtoseconds) hot electron decay times observed experimentally arise from electron–phonon scattering. This result is an important advance to resolve a controversy on hot electron cooling in GaAs. We further find that, contrary to common notions, all optical and acoustic modes contribute substantially to electron–phonon scattering, with a dominant contribution from transverse acoustic modes. This work provides definitive microscopic insight into hot electrons in GaAs and enables accurate ab initio computation of hot carriers in advanced materials.

scholarly journals Hot-carrier dynamics in InAs/AlAsSb multiple-quantum wells

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Herath P. Piyathilaka ◽  
Rishmali Sooriyagoda ◽  
Hamidreza Esmaielpour ◽  
Vincent R. Whiteside ◽  
Tetsuya D. Mishima ◽  
...  
Keyword(s):  
Band Gap ◽  
Photon Energy ◽  
Metastable State ◽  
Carrier Dynamics ◽  
Multiple Quantum ◽  
Hot Carriers ◽  
Defect States ◽  
Energy Excitation ◽  
Hot Carrier ◽  
Decay Times

AbstractA type-II InAs/AlAs$$_{0.16}$$ 0.16 Sb$$_{0.84}$$ 0.84 multiple-quantum well sample is investigated for the photoexcited carrier dynamics as a function of excitation photon energy and lattice temperature. Time-resolved measurements are performed using a near-infrared pump pulse, with photon energies near to and above the band gap, probed with a terahertz probe pulse. The transient terahertz absorption is characterized by a multi-rise, multi-decay function that captures long-lived decay times and a metastable state for an excess-photon energy of $$>100$$ > 100 meV. For sufficient excess-photon energy, excitation of the metastable state is followed by a transition to the long-lived states. Excitation dependence of the long-lived states map onto a nearly-direct band gap ($$E{_g}$$ E g ) density of states with an Urbach tail below $$E{_g}$$ E g . As temperature increases, the long-lived decay times increase $$<E{_g}$$ < E g , due to the increased phonon interaction of the unintentional defect states, and by phonon stabilization of the hot carriers $$>E{_g}$$ > E g . Additionally, Auger (and/or trap-assisted Auger) scattering above the onset of the plateau may also contribute to longer hot-carrier lifetimes. Meanwhile, the initial decay component shows strong dependence on excitation energy and temperature, reflecting the complicated initial transfer of energy between valence-band and defect states, indicating methods to further prolong hot carriers for technological applications.

scholarly journals Observation of a phonon bottleneck in copper-doped colloidal quantum dots

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Lifeng Wang ◽  
Zongwei Chen ◽  
Guijie Liang ◽  
Yulu Li ◽  
Runchen Lai ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Cadmium Selenide ◽  
Phonon Scattering ◽  
Photochemical Reactions ◽  
Hot Electrons ◽  
Colloidal Quantum Dots ◽  
Hot Electron ◽  
Electron Cooling ◽  
Phonon Bottleneck ◽  
Cooling Mechanism

Abstract Hot electrons can dramatically improve the efficiency of solar cells and sensitize energetically-demanding photochemical reactions. Efficient hot electron devices have been hindered by sub-picosecond intraband cooling of hot electrons in typical semiconductors via electron-phonon scattering. Semiconductor quantum dots were predicted to exhibit a “phonon bottleneck” for hot electron relaxation as their quantum-confined electrons would couple very inefficiently to phonons. However, typical cadmium selenide dots still exhibit sub-picosecond hot electron cooling, bypassing the phonon bottleneck possibly via an Auger-like process whereby the excessive energy of the hot electron is transferred to the hole. Here we demonstrate this cooling mechanism can be suppressed in copper-doped cadmium selenide colloidal quantum dots due to femtosecond hole capturing by copper-dopants. As a result, we observe a lifetime of ~8.6 picosecond for 1Pe hot electrons which is more than 30-fold longer than that in same-sized, undoped dots (~0.25 picosecond).

Electron–phonon scattering and mean free paths in D-carbon

2020 ◽  
Vol 22 (7) ◽  
pp. 4010-4014
Author(s):  
Xiangtian Bu ◽  
Shudong Wang
Keyword(s):  
First Principles ◽  
Phonon Scattering ◽  
Interpolation Method ◽  
Wannier Function ◽  
Hot Carrier ◽  
Carrier Scattering ◽  
Electron Phonon Scattering ◽  
Scattering Rates

Through first-principles simulations combined with the Wannier function interpolation method, the hot carrier scattering rates of D-carbon are studied.

scholarly journals Highly efficient hot electron harvesting from graphene before electron-hole thermalization

2019 ◽  
Vol 5 (11) ◽  
pp. eaax9958 ◽  
Author(s):  
Yuzhong Chen ◽  
Yujie Li ◽  
Yida Zhao ◽  
Hongzhi Zhou ◽  
Haiming Zhu
Keyword(s):  
Solar Cell ◽  
Quantum Yield ◽  
Nonlinear Behavior ◽  
Hot Electrons ◽  
Hot Electron ◽  
New Paradigm ◽  
Electron Hole ◽  
Mid Infrared ◽  
Hot Carrier ◽  
Carrier Thermalization

Although the unique hot carrier characteristics in graphene suggest a new paradigm for hot carrier–based energy harvesting, the reported efficiencies with conventional photothermoelectric and photothermionic emission pathways are quite low because of inevitable hot carrier thermalization and cooling loss. Here, we proposed and demonstrated the possibility of efficiently extracting hot electrons from graphene after carrier intraband scattering but before electron-hole interband thermalization, a new regime that has never been reached before. Using various layered semiconductors as model electron-accepting components, we generally observe ultrafast injection of energetic hot electrons from graphene over a very broad photon energy range (visible to mid-infrared). The injection quantum yield reaches as high as ~50%, depending on excitation energy but remarkably, not on fluence, in notable contrast with conventional pathways with nonlinear behavior. Hot electron harvesting in this regime prevails over energy and carrier loss and closely resembles the concept of hot carrier solar cell.

scholarly journals Hot carrier relaxation in Cs2TiIyBr6−y (y = 0, 2 and 6) by a time-domain ab initio study

RSC Advances ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 958-964 ◽  
Author(s):  
Hejin Yan ◽  
Yingfeng Li ◽  
Xiang Li ◽  
Bingxin Wang ◽  
Meicheng Li
Keyword(s):  
Relaxation Time ◽  
Ab Initio ◽  
Time Domain ◽  
Ab Initio Study ◽  
Hot Carriers ◽  
Carrier Relaxation ◽  
Hot Carrier

The hot carriers within 10 nm from the Cs2TiIyBr6−y/TiO2 interface can be extracted effectively due to their 2–3 ps relaxation time.

scholarly journals Spin blockade and phonon bottleneck for hot electron relaxation observed in n-doped colloidal quantum dots

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Junhui Wang ◽  
Lifeng Wang ◽  
Shuwen Yu ◽  
Tao Ding ◽  
Dongmei Xiang ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Phonon Scattering ◽  
Surface States ◽  
Hot Electrons ◽  
Hot Electron ◽  
Phonon Bottleneck ◽  
Spin Interactions ◽  
Doped Quantum Dots ◽  
Electron Relaxation ◽  
Spin Blockade

AbstractUnderstanding and manipulating hot electron dynamics in semiconductors may enable disruptive energy conversion schemes. Hot electrons in bulk semiconductors usually relax via electron-phonon scattering on a sub-picosecond timescale. Quantum-confined semiconductors such as quantum dots offer a unique platform to prolong hot electron lifetime through their size-tunable electronic structures. Here, we study hot electron relaxation in electron-doped (n-doped) colloidal CdSe quantum dots. For lightly-doped dots we observe a slow 1Pe hot electron relaxation (~10 picosecond) resulting from a Pauli spin blockade of the preoccupying 1Se electron. For heavily-doped dots, a large number of electrons residing in the surface states introduce picosecond Auger recombination which annihilates the valance band hole, allowing us to observe 300-picosecond-long hot electrons as a manifestation of a phonon bottleneck effect. This brings the hot electron energy loss rate to a level of sub-meV per picosecond from a usual level of 1 eV per picosecond. These results offer exciting opportunities of hot electron harvesting by exploiting carrier-carrier, carrier-phonon and spin-spin interactions in doped quantum dots.

Temperature Dependence of Hot Carrier Relaxation in a PBSE Quantum Dot: An Ab Initio Study

2009 ◽  
Author(s):  
Hua Bao ◽  
Xiulin Ruan ◽  
Bradley F. Habenicht ◽  
Oleg V. Prezhdo
Keyword(s):  
Low Temperature ◽  
Quantum Dot ◽  
Ab Initio ◽  
Temperature Dependence ◽  
Occupation Number ◽  
Relaxation Rates ◽  
Hot Carriers ◽  
Phonon Modes ◽  
Hot Carrier ◽  
Higher Temperature

Temperature dependent dynamics of phonon-assisted relaxation of hot carriers, both electrons and holes, is studied in a PbSe quantum dot using ab initio time-domain density functional theory. The electronic structure is first calculated, showing that the hole states are denser than the electron states. Fourier transforms of the time resolved energy levels show that the hot carriers couple to both acoustic and optical phonons. At higher temperature, more phonon modes in the high frequency range participate in the relaxation process due to their increased occupation number. The phonon-assisted hot carrier decay dynamics is predicted using non-adiabatic molecular dynamics, and the calculated relaxation rates clearly show a temperature-activation behavior. The complex temperature dependence is attributed to the combined effects of the phonon occupation number and thermal expansion. Comparing the simulation results with experiments, we suggest that the multiphonon relaxation channel is efficient at high temperature, while the Auger-like process may dominate the relaxation at low temperature. This combined mechanism can explain the weak temperature dependence at low temperature and stronger temperature dependence at higher temperature.

A Study of Quasi-Breakdown Mechanism in Ultrathin Gate Oxide Under Various Types of Stress

1999 ◽  
Vol 592 ◽  
Author(s):  
Hao Guan ◽  
Zhen Xu ◽  
Byung Jin Cho ◽  
M. F. Li ◽  
Y. D. He
Keyword(s):  
Damage Model ◽  
Gate Oxide ◽  
Interface State ◽  
Hot Electron ◽  
Hot Carriers ◽  
Hot Carrier ◽  
Interface Damage ◽  
Breakdown Mechanism ◽  
State Generation ◽  
Thin Gate Oxide

ABSTRACTThe quasi-breakdown (QB) in ultra thin gate oxide is investigated through the observation of defect generation during high field F-N stress and substrate hot hole and hot electron stresses. The interface trap density increases during stress and reaches to a same critical amount at the onset point of QB regardless of stress current density and stressing carrier type. The experiments also show that hot carriers are much more effective to trigger QB than F-N electrons at the same current level. This can be ascribed to the fact that hot carrier has much higher interface state generation rate than F-N electron does. All results consistently support the interface damage model for the QB occurrence.

EFFECT OF INELASTIC SCATTERING OF HOT ELECTRONS ON THERMIONIC COOLING IN A SINGLE-BARRIER STRUCTURE

2000 ◽  
Vol 14 (14) ◽  
pp. 1451-1457
Author(s):  
C. ZHANG
Keyword(s):  
Inelastic Scattering ◽  
Room Temperature ◽  
Phonon Scattering ◽  
Hot Electrons ◽  
Electron Interaction ◽  
Barrier Structure ◽  
Phonon Interaction ◽  
Electron Phonon Interaction ◽  
Barrier Region ◽  
Electron Phonon Scattering

One of the important problems in thermionics using layered structures is the inelastic scattering of hot electrons in the electrodes and in the barrier region. Scattering in these systems is mainly via the electron–phonon interaction, or indirectly via the electron–electron interaction. In semiconductor heterostructures at room temperature, the LO-phonon plays a crucial role in thermalising electrons. In this work we study the effect of electron–phonon scattering on thermionic cooling in a single-barrier structure. Because of the asymmetry of the barrier under a bias, a larger fraction of the total energy loss will be dissipated in the hot electrode. As a result, we find that the theoretical thermal efficiency can increase due to limited electron–phonon scattering.

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