Ultraefficient Terahertz Emission Mediated by Shift-Current Photovoltaic Effect in Layered Gallium Telluride

Abstract

Generating terahertz waves using thin-layered materials holds great potential for the realization of integrated terahertz devices. However, previous studies have been limited by restricted radiation intensity and finite efficiency. Exploiting materials with higher efficiency for terahertz emission has attracted increasing interest worldwide. Herein, with visible-light excitation, a thin-layered GaTe film is demonstrated to be a promising emitter of terahertz radiation induced by the shift-current photovoltaic effect. Through theoretical calculations, a transient charge-transfer process resulting from the asymmetric structure of GaTe is shown to be the origin of an ultrafast shift current. Furthermore, it was found that the amplitude of the resulting terahertz signals can be manipulated by both the fluence of the pump laser and the orientation of the sample. Such high emission efficiency from the shift current indicates that the layered material (GaTe) is an excellent candidate for photovoltaics and terahertz emitters.

Highly Efficient Spintronic Terahertz Emitter Utilizing a Large Spin Hall Conductivity of Type-II Dirac Semimetal PtTe2

“…It is notable that the THz waveforms at different angles of polarization exhibit no significant difference, and there is no appreciable change with the incident pump polarization (for linear and circular). This result contrasts with those for Bi 2 Se 3 /Co-STE, and other single-layer systems such as GaTe and MoSe 2 in which a sinusoidal dependence on the polarization angle was found. This sinusoidal dependence is due to the asymmetric structure of the crystal that results in nonlinear optical effects in the system .…”

Giant Photon‐Drag‐Induced Ultrafast Photocurrent in Diamond for Nonlinear Photonics

“…As for the nonlinear optical processes, the ultrafast photocurrent can be introduced by either photogalvanic effect (PGE) or photon drag effect (PDE). From the PGE point of view, the ultrafast photocurrent is dominated by the spatial shift of the charge center along the atom‐to‐atom bonds in anti‐centrosymmetric materials, [ 40 ] which is more susceptible to occur in semiconductors or topological insulators in principle, such as Bi 2 Se 3 , [ 41 ] GaTe, [ 42 ] and Bi 2 Te 3 . [ 43 ] Besides, according to the azimuthal angle dependence of THz amplitude in Figure 1e, the CVD diamond exhibits isotropy with surface symmetry.…”

Piezoelectric Strain Control of Terahertz Spin Current

“…[17,25,26] Achieving the active control of such sub-picosecond THz spin current pulses and the resulting THz radiation pulse emitted from the fs photoexcitation of THz spintronic emitter is highly desirable to fabricate the on-chip optospintronic devices for potential applications in high-speed computing [27] and memory devices with different functionalities. [28] Several other systems have also been opted to design terahertz emitters such as shift currentbased system, [29] Rashba-type interfaces, [30] ferromagnetic/ antiferromagnetic interface-based system, [31] cross-bar design consisting of ferromagnet with positive and negative spin Hall materials for coding and programmable devices. [32] The control of the THz spin current through electrical current, [33] magnetic field, [34,35] photothermal effect, [36] anisotropy modulation, [37] and helicity of light [34] have been demonstrated.…”