15:00 〜 15:15
▲ [22p-F407-8] Terahertz emission from single crystal MoSe2
キーワード：transition metal dichalcogenides, terahertz emission
Transition metal dichalcogenides or “TMDCs” (e.g. M=Mo, X=S, Se, Te) can form hexagonal MX2. These layered materials are weakly bonded and can be made atomically thin. TMDCs have unusual physical properties including, but not limited to, very high exciton binding energies and thickness- and strain-dependent band gaps [1]. In bulk form, MoSe2 is semiconducting and has an indirect band gap from K(VB)-->G-K(CB) with an energy of around ~1.4 eV, and a pair of local conduction band and valence band extrema at its K point, with the K(VB)-->K(CB) transition energy approximately ~1.57 eV [2].
To investigate the ultrafast photoexcited carriers and lattice dynamical interactions, we studied wavelength- (775 nm – 830 nm) and fluence- (14 - 103 nJ/cm2) dependent terahertz (THz) emission from bulk, single crystal MoSe2. The sample used here was grown using physical vapor transport. Time-domain THz emission spectroscopy was performed by exciting the MoSe2 surface using a femtosecond laser (repetition rate 80 MHz, pulse width ~70 fs) and detecting the THz emission using a LT-GaAs photoconductive antenna. Fig. 1 (left) shows the fluence-dependence of the THz emission when excited at 795 nm (1.56 eV). The amplitude increases with fluence, while the emission bandwidth (inset) extends to ~2.5 THz. The emission amplitude is approximately 1/6 relative to undoped InAs. Fig. 1 (right) shows the wavelength dependence of the THz peak. THz emission amplitude is highest when pumped at 1.56 eV, which coincides with energy of the suspected K-point of MoSe2 [3]. At this pump energy, photoexcitation is most efficient due to the direct transition of photocarriers. The effect is prominent at higher fluence values.
To investigate the ultrafast photoexcited carriers and lattice dynamical interactions, we studied wavelength- (775 nm – 830 nm) and fluence- (14 - 103 nJ/cm2) dependent terahertz (THz) emission from bulk, single crystal MoSe2. The sample used here was grown using physical vapor transport. Time-domain THz emission spectroscopy was performed by exciting the MoSe2 surface using a femtosecond laser (repetition rate 80 MHz, pulse width ~70 fs) and detecting the THz emission using a LT-GaAs photoconductive antenna. Fig. 1 (left) shows the fluence-dependence of the THz emission when excited at 795 nm (1.56 eV). The amplitude increases with fluence, while the emission bandwidth (inset) extends to ~2.5 THz. The emission amplitude is approximately 1/6 relative to undoped InAs. Fig. 1 (right) shows the wavelength dependence of the THz peak. THz emission amplitude is highest when pumped at 1.56 eV, which coincides with energy of the suspected K-point of MoSe2 [3]. At this pump energy, photoexcitation is most efficient due to the direct transition of photocarriers. The effect is prominent at higher fluence values.