Enhanced Modulation of Terahertz Generation in Optically Pumped Silicon-Based CoFeB/Ir Heterostructures

Silicon-compatible spintronic terahertz emitters (STEs) are crucial for on-chip ultrafast optoelectronic integration, yet their all-optical controllability remains a key challenge. Here, we fabricate a Ta-buffered CoFeB/Ir heterostructure on Si substrates and realize, for the first time, the enhancement and nonlinear modulation of coherent THz emission under continuous-wave (CW) optical pumping at room temperature. The THz emission, dominated by the inverse spin Hall effect, features an ultrabroad 0-2.5 THz bandwidth and robustness against femtosecond pump fluence and polarization variations. The all-optical modulation of THz generation originates from the competition between photothermal and photodoping effects in the Si substrate. The heterostructure-side pumping with a 450 nm CW laser yields an increased modulation of 46% at 2.546 W cm^-2 due to the photothermal effect, while the Si substrate-side pumping at 780 nm leads to 21.3% THz emission suppression by photodoping. Moreover, the THz enhanced modulation efficiency peaks at an Ir layer thickness of 1.2 nm. Our work demonstrates an all-optical controllable Si-based THz source, providing critical insights for the design of next-generation on-chip THz functional devices.