Ultrafast carrier dynamics in Ge by ultra-broadband mid-infrared probe spectroscopy

Abstract

In this study, we carried out 800-nm pump and ultra-broadband mid-infrared (MIR) probe spectroscopy with high time-resolution (70 fs) in bulk Ge. By fitting the time-resolved difference reflection spectra [ΔR(ω)/R(ω)] with the Drude model in the 200–5000 cm−1 region, the time-dependent plasma frequency and scattering rate have been obtained. Through the calculation, we can further get the time-dependent photoexcited carrier concentration and carrier mobility. The Auger recombination essentially dominates the fast relaxation of photoexcited carriers within 100 ps followed by slow relaxation due to diffusion. Additionally, a novel oscillation feature is clearly found in time-resolved difference reflection spectra around 2000 cm−1 especially for high pump fluence, which is the Lorentz oscillation lasting for about 20 ps due to the Coulomb force exerted just after the excitation.

Controllable all-optical modulation speed in hybrid silicon-germanium devices utilizing the electromagnetically induced transparency effect

“…From these two figures, one can clearly observe a slow and a fast photo-switching cycle in false color images without crosstalk between each other. The penetration depth of the 800 nm laser in Si and Ge materials are 1176 and 203 nm [49,58], respectively. A 600-nm Ge film is sufficient to absorb all incident light, but the epitaxial Si film cannot block the pump pulses totally.…”

“…Similar to Si, Ge is an indirect bandgap semiconductor, whose fundamental energy bandgap is 0.66 eV (0.14 eV lower than the direct bandgap), and also exhibits great potential for dynamic modulation. Compared with Si, Ge possesses a larger intrinsic carrier concentration and a higher carrier mobility [49,50] as well as good compatibility with complementary metal-oxide-semiconductor foundries. In our device layout, Ge is simply evaporated as single layer over the Fano-resonant metamaterial array on the epitaxially grown SoS substrate.…”

“…In our device layout, Ge is simply evaporated as single layer over the Fano-resonant metamaterial array on the epitaxially grown SoS substrate. Different from the ErAs/GaAs superlattices where ultrafast photoswitching of inductive-capacitive (LC) resonances were achieved previously [51], amorphous Ge has structural defects that result in trap-assisted recombination sites [49,52], which helps promote ultrafast carrier recombination (around three orders of magnitude faster than superlattices) and the device fabrication based on it requires no alternating between materials. This is because it only involves the deposition of a single-element semiconductor film, instead of satisfying the lattice matching condition.…”

Development and Application of Sub-Cycle Mid-Infrared Source Based on Laser Filamentation

“…For example, structural dynamics of molecules in the femtosecond time scale was investigated with ultrafast pump-probe spectroscopy using the ultrabroadband MIR probe pulse [9][10][11], free-carrier dynamics in semiconductors were clearly observed in the very wide range of the probe energy [12][13][14], and two-dimensional spectroscopy with the ultrabroadband MIR probe was experimentally demonstrated [15,16].…”

“…The authors combined the chirped-pulse upconversion technique with the femtosecond 69 pump-probe spectroscopy [12,14] and attenuated total reflection spectroscopy (ATR) [23,24]. As a 70 demonstration of the ATR combined with CPU, the MIR absorption spectra of acetic acid (CH 3 COOH,…”