Attosecond-fast internal photoemission

Abstract

The photoelectric effect has a sister process relevant in optoelectronics called internal photoemission [13]. Here an electron is photoemitted from a metal into a semiconductor [4,5]. While the photoelectric effect takes place within less than 100 attoseconds (1 as = 10 −18 seconds) [6,7], the attosecond time scale has so far not been measured for internal photoemission. Based on the new method CHArge transfer time MEasurement via Laser pulse duration-dependent saturation fluEnce determinatiON CHAMELEON , we show that the atomically thin semi-metal graphene coupled to bulk silicon carbide, forming a Schottky junction, allows charge transfer times as fast as (300±200) attoseconds. These results are supported by a simple quantum mechanical model simulation. With the obtained cut-off bandwidth of 3.3 PHz (1 PHz = 10 15 Hz) for the charge transfer rate, this semimetalsemiconductor interface represents a functional solid-state interface offering the speed and design space required for future light-wave signal processing.The transfer of charge via internal photoemission at a solid-state interface is a fundamental process with direct relevance in ultrafast optoelectronics [24] and the transduction of light to chemical or electrical energy in light-harvesting [811]. Various solid state-based interfaces have been investigated to study the ultimate speed of this fundamental process using optical methods [2,3,12,13]. Time constants for the charge transfer in the attosecond domain (∼100 as) have so far only been observed in photoemission from metal surfaces or atoms into vacuum [6,7,14] or from atoms/molecules to metals [1517]; part of these experiments infer the charge transfer rates based on the uncertainty principle [12,18]. Similarly, excited charges may oscillate within a molecule from one part of the molecule to another within hundreds of attoseconds [10]. In stark contrast, in materials relevant for fast electronics, such as layered heterostructures with atomically sharp interfaces, the hitherto fastest charge transfer time reported was about 7 fs * in a grapheneboron nitridegraphene layered heterostructures [12]. Achieving faster time scales has proven impossible so far because of the formation of excitons, which are bound states of the photo-generated electron-hole pair [2,8], or quantum mechanical backreflection [10], taking precedence over charge separation. The ideal system to achieve attosecond-fast charge separation at a solid-state interface resembles the photoelectric effect, so external photoemission from a metal into vacuum [6,7]: It is strongly asymmetric with only one side optically absorbing; it has an atomically sharp interface, reducing the electron transfer distance; in addition to its external counterpart it has a strong built-in electric field that promotes fast transfer of electrons into the electronabsorbing half-space, i.e., the acceptor material. Electron absorption at such an extended acceptor might preserve electronic coherence but hinders the carrier wavefunction to sling back to the donor ma...

Hot carriers in graphene – fundamentals and applications

“…By modelling the dependence of the photocurrent on the laser pulse duration, a tunneling time as short as ∼0.3 fs was extracted, which offers exciting perspectives for applications in ultrafast electronics. 244 …”

“…By modelling the dependence of the photocurrent on the laser pulse duration, a tunneling time as short as ∼0.3 fs was extracted, which offers exciting perspectives for applications in ultrafast electronics. 244 The dynamics of interlayer charge transport in g/TMD junctions have recently been the focus of several optical pumpprobe studies. [245][246][247] While all studies have observed the generation of photocarriers in the TMD layer after sub-bandgap photon energies, its origin is still debated.…”

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

“…Recently, the internal photoemission between graphene/SiC interface has been successfully explained by using the Liang–Ang thermionic model and a two‐temperature photoemission model (Figure 7(C)). 143 The Liang–Ang model has been extended into few‐layer graphene, and it is found that the thermionic emission current is sensitively influenced by the layer number and the stacking configurations (see Figure 7(E)). 62 …”

“…Copyright 2017, IEEE. (C) Schematic drawing of internal photoemission in graphene/SiC contact 143 . Copyright 2020, Nature Publishing Group.…”

Coherent control of collective nuclear quantum states via transient magnons

“…Temporal control of quantum phases yields fundamental knowledge about quantum systems (14)(15)(16)(17)(18)(19) and is a cornerstone of many quantum technologies (17,20). Nowadays, attosecond electronic processes can be captured in atoms (21,22), molecules (23), or condensed matter (24,25), leading to the basic understanding of quantum phenomena like tunneling (26), ionization of molecules (27), or electron scattering (24). To achieve this, small time delays, or the corresponding phases, of the system have to be monitored.…”