Optically Controlled Extraordinary Terahertz Transmission of Bi2Se3 Film Modulator

Abstract

Standing on the potential for high-speed modulation and switching in the terahertz (THz) regime, all-optical approaches whose response speeds mainly depend on the lifetime of nonequilibrium free carriers have attracted a tremendous attention. Here, we establish a novel bi-direction THz modulation experiment controlled by femtosecond laser for new functional devices. Specifically, time-resolved transmission measurements are conducted on a series of thin layers Bi 2 Se 3 films fabricated straightforwardly on Al 2 O 3 substrates, with the pump fluence range from 25 μJ/cm 2 to 200 μJ/cm 2 per pulse. After photoexcitation, an ultrafast switching of THz wave with a full recovery time of ~10 ps is observed. For a longer timescale, a photoinduced increase in the transmitted THz amplitude is found in the 8 and 10 quintuple layers (QL) Bi 2 Se 3 , which shows a thickness-dependent topological phase transition. Additionally, the broadband modulation effect of the 8 QL Bi 2 Se 3 film is presented at the time delays of 2.2 ps and 12.5 ps which have a maximum modulation depth of 6.4% and 1.3% under the pump fluence of 200 μJ/cm 2 , respectively. Furthermore, the absorption of α optical phonon at 1.9 THz shows a time-dependent evolution which is consistent with the cooling of lattice temperature.

Transient THz Study of Phonon-Assisted Carrier Scattering between Bulk and Surface States in Bi2Te3

“…Surprisingly, the THz transmission dropping process in our Bi 2 Te 3 film reaches about 3 ps, which can be clearly seen from the inset in Figure a. This slow-dropping process in our 300 nm-thick Bi 2 Te 3 film shows very different features from those of few-layered TIs, − graphene, and conventional semiconductors. − In addition, the maximum modulation depth, |Δ T / T 0 | max (Δ T = T 0 – T with T 0 and T of the THz peak transmission without and with pump beam, respectively), shows a nonlinear dependence with respect to the pump fluence as illustrated in Figure b. It is noted that saturation intensities for Bi 2 Se 3 and Bi 2 Te 3 films are about 4.3 and 6.0 GW/cm 2 , respectively, , which is 2 orders of magnitude higher than the maximum optical intensity used in this study.…”

Temperature-Dependent Evaluation of Charge Carriers and Terahertz Generation in Bismuth and Antimony-Based Chalcogenides

“…The terahertz frequency range of 0.03 to 5.2 THz is created by a single crystal of Bi 2 Se 3 [14,[26][27][28][29][30][31][32][33][34][35][36][37][38]. In summary, phonons, which are the COP in bismuth selenide, are responsible for generating the terahertz frequency, as mentioned in the TRUS section above.…”

“…In summary, phonons, which are the COP in bismuth selenide, are responsible for generating the terahertz frequency, as mentioned in the TRUS section above. The terahertz spectroscopy directly validates the 2 THz frequency generation, while the TRUS was the initial method by which these oscillations were originally seen [14,18,26,30,32,34,36,37,[39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] and was used to confirm the frequency of the 2 THz frequency. In addition, Prince Sharma et al in 2020 contrasted assessing the frequency determined through TRUS, revealing the COP oscillations [34,48] to evaluate the frequency from the kinetic spectrum.…”

2D THz Optoelectronics

“…presented results on Bi 2 Se 3 films grown on Al 2 O 3 . [ 97 ] Interestingly, in this material the THz transmission is quenched in the first few picoseconds after pumping, while after about 10 ps the THz transmission is increased due to a topological phase transition.…”