Hot-electron emission processes in waveguide-integrated graphene

Cao

2021

InfoMat

Electrically contacting two‐dimensional (2D) materials is an inevitable process in the fabrication of devices for both the study of fundamental nanoscale charge transport physics and the design of high‐performance novel electronic and optoelectronic devices. The physics of electrical contact formation and interfacial charge injection critically underlies the performance, energy‐efficiency and the functionality of 2D‐material‐based devices, thus representing one of the key factors in determining whether 2D materials can be successfully implemented as a new material basis for the development of next‐generation beyond‐silicon solid‐state device technology. In this review, the recent developments in the theory and the computational simulation of electron emission, interfacial charge injection and electrical contact formation in 2D material interfaces, heterostructures, and devices are reviewed. Focusing on thermionic charge injection phenomena which are omnipresent in 2D‐materials‐based metal/semiconductor Schottky contacts, we summarize various transport models and scaling laws recently developed for 2D materials. Recent progress on the first‐principle density functional theory simulation of 2D‐material‐based electrical contacts are also reviewed. This review aims to provide a crystalized summary on the physics of charge injection in the 2D Flatlands for bridging the theoretical and the experimental research communities of 2D material device physics and technology.

τ_{⊥}^{- 1} ((),, ε_{bold-italick}, V)

Section: Theory Of Electron Injection In 2d‐material‐based Hetero‐interfacesmentioning

confidence: 99%

Physics of electron emission and injection in two‐dimensional materials: Theory and simulation

Cao

2021

InfoMat

“…These nonequilibrium hot electrons therefore go through different scattering mechanisms where they lose energy and thermalize. The most prominent scattering mechanisms in graphene are: (1) electron-electron (e-e) scattering, (2) optical phonon (OP) scattering, and (3) supercollision acoustic phonon (SC) scattering [12,[21][22][23][24][25][26][27][28]. While e-e scattering allows the hot electrons to elastically redistribute their excess energy among the "cold" electrons in the Fermi sea, both OP and SC scattering cause them to lose energy to the lattice.…”

Section: Hot Electron Emission Mechanism In Graphenementioning

confidence: 99%

“…Multi-photon and strong-field emitters allow the use of lower photon energy lasers, potentially enabling the use of compact semiconductor lasers and integrated photonics, but require high power densities (> 1015 W/m2), which typically necessitate the use of ultra-fast pulsed lasers [7][8][9][10][11]. Recently, it has been shown that hot electrons in graphene can mediate photoemission from sub-workfunction photons at power densities over 5 orders of magnitude lower than metal tips [12].…”

Section: Introductionmentioning

confidence: 99%

“…Favorable scattering rates in graphene also allowed the photoexcited hot electrons to be emitted into vacuum before thermalizing down to the Fermi level. Due to these features of graphene, it has been shown that hot electron emission from waveguide integrated graphene using subworkfunction photons can occur at power densities that are multiple orders of magnitude lower than metallic tips emitters [12][13][14][15]. Previously, it was shown that an electron emission model obtained by solving the nonequilibrium Monte Carlo Boltzmann transport equation (MCBTE) could quantitatively explain the nature of the observed current density as a function of the applied electric field, optical power density and photon energy [12,16].…”

Section: Introductionmentioning

confidence: 99%

“…Due to these features of graphene, it has been shown that hot electron emission from waveguide integrated graphene using subworkfunction photons can occur at power densities that are multiple orders of magnitude lower than metallic tips emitters [12][13][14][15]. Previously, it was shown that an electron emission model obtained by solving the nonequilibrium Monte Carlo Boltzmann transport equation (MCBTE) could quantitatively explain the nature of the observed current density as a function of the applied electric field, optical power density and photon energy [12,16]. In addition, there has been a number of theoretical studies on graphene based Schottky barrier devices modeling the thermionic and photoexcited electron emission of electrons over the barrier as well as on generalized 2D material based Schottky barrier devices [17][18][19][20].…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Performance Limits of Graphene Hot Electron Emission Photoemitters

et al. 2020

Self Cite

Hot electron emission from waveguide integrated graphene has been recently shown to occur at optical power densities multiple orders of magnitude lower than metal tips excited by subworkfunction photons. However, the experimentally observed electron emission currents were small, limiting the practical uses of such a mechanism. Here, we explore the performance limits of hot electron emission in graphene through experimentally calibrated simulations. Two regimes of non-equilibrium emission in graphene are identified, (i) single particle hot electron emission, where an electron is excited by a photon, and is emitted before losing significant energy through scattering, and (ii) ensemble hot electron emission, where the photon source causes nonequilibrium heating of the electron population beyond the electron lattice temperature. It is shown that through appropriate selection of photon energy, optical power density, and applied electric field hot electron emission can be used to create ultra-high current electron emitters with ultra-fast temporal responses in both the single particle and ensemble heating regimes. These results suggest that through appropriate design, hot electron emitters may overcome the limitations of thermionic and field emitters.

Increasing the Hot‐Electron Driven Hydrogen Evolution Reaction Rate on a Metal‐Free Graphene Electrode

Chae

Ahsan

Teishima

et al. 2021

Adv Materials Inter

Self Cite

Recently, it has been shown that a semiconductor–insulator–graphene device can drive the hydrogen evolution reaction (HER) at the graphene surface with a reduced onset potential by injecting hot electrons into graphene. However, the catalytic properties of graphene are limited by the large hydrogen adsorption energy and lack of electrochemically active sites. To address these limitations, a n‐silicon/insulator/plasma etched graphene device is investigated, where a dry etch process is used to increase the number of active sites on the graphene by creating a greater number of active edge sites, increasing hydrogen adsorption at a given potential. This has been shown to improve the properties of devices with cold electrons. However, here it is shown that this approach can improve the HER rate with hot electrons. The electrons injected into the graphene from the silicon shift the onset potential of HER by as high as ≈0.8 V reaching a current density of 90 mA cm−2 at an overpotential of ‐0.5 V versus RHE. Furthermore, the comparison between device with pristine graphene shows a ≈2X improvement in current density at high overpotentials. This result shows that hot‐electron devices can be improved by modifying the catalytically active sites without metal catalysts.