講演情報
[11a-A22-2]Terahertz emission from MoS2 thin films around the C-exciton absorption region
〇TIANKAI JIA1, Manjakavahoaka Razanoelina1, Takumi Ikenoue1, Toshiyuki Kawaharamura2, Iwao Kawayama1 (1.Kyoto Univ., 2.Kochi Univ. of Tech.)
キーワード：
terahertz emission spectroscopy、MoS2、C-exciton
Layered transition-metal dichalcogenides (TMDCs) such as MoS2 are promising materials for ultrafast optoelectronics because of their strong excitonic optical responses. Terahertz emission spectroscopy (TES) offers a powerful, non-contact probe of such ultrafast responses, because the emitted THz field reflects sub-picosecond photocurrents and nonlinear polarization induced immediately after photoexcitation. Terahertz (THz) emission from MoS2 has been attributed to surface optical rectification and surface-field-induced transient photocurrent. However, the wavelength-dependent THz emission behavior in the short-wavelength excitation region remains unclear.
In this study, we investigate THz emission from MoS2 films under femtosecond excitation with wavelengths ranging from 460 to 360 nm. The data shown here were obtained from a representative MoS2 film prepared on soda-lime glass by mist chemical vapor deposition, and its thickness was approximately 20–30 nm. As the excitation wavelength decreases from 460 to 420 nm, the THz amplitude increases steeply and then remains nearly constant in the 360–420 nm range (Fig. 1(a)). Fluence-dependent measurements in the weak-excitation regime indicate that this plateau is unlikely to originate from excitation saturation under the present experimental conditions: the amplitude scales linearly with fluence at all wavelengths, while the generation efficiencies at 380 and 400 nm are larger and nearly identical to each other, compared with that at 440 nm (Fig. 1(b)).
This behavior may reflect a nearly wavelength-independent effective THz source in this spectral range, where enhanced optical transitions associated with the C-exciton and band nesting contribute to efficient carrier generation. These results suggest that the wavelength dependence of THz emission can provide insight into photoexcited carrier generation in MoS2 around the C-exciton absorption region.
In this study, we investigate THz emission from MoS2 films under femtosecond excitation with wavelengths ranging from 460 to 360 nm. The data shown here were obtained from a representative MoS2 film prepared on soda-lime glass by mist chemical vapor deposition, and its thickness was approximately 20–30 nm. As the excitation wavelength decreases from 460 to 420 nm, the THz amplitude increases steeply and then remains nearly constant in the 360–420 nm range (Fig. 1(a)). Fluence-dependent measurements in the weak-excitation regime indicate that this plateau is unlikely to originate from excitation saturation under the present experimental conditions: the amplitude scales linearly with fluence at all wavelengths, while the generation efficiencies at 380 and 400 nm are larger and nearly identical to each other, compared with that at 440 nm (Fig. 1(b)).
This behavior may reflect a nearly wavelength-independent effective THz source in this spectral range, where enhanced optical transitions associated with the C-exciton and band nesting contribute to efficient carrier generation. These results suggest that the wavelength dependence of THz emission can provide insight into photoexcited carrier generation in MoS2 around the C-exciton absorption region.