Spintronic THz Emission in Wide-bandgap Semiconductor Heterostructures

The generation and detection of terahertz (THz) radiation have many potential applications ranging from high-speed communications to surveillance. Accessing a broad range of THz frequencies is a significant challenge for realizing THz applications. A spintronic method for THz generation in ferromagnetic/non-magnetic heterostructures is an emerging approach for producing THz fields. Here, the principle of operation is based on ultrafast demagnetization of the ferromagnetic layer in response to an incident, femtosecond laser pulse, followed by ultrafast decay of the resulting superdiffusive spin current into the non-magnetic layerthat leads to a transient THz pulse. Here we demonstrate spintronic THz generation in heterostructures comprising wide-bandgap semiconductors instead of heavy metals. These wide-bandgap semiconductors possess strong Rashba states due to their non-centrosymmetric crystal structures that are favorable for efficient spin-to-charge conversion for spintronic THz generation. In addition, their electrically tunable characteristics induced by chemical doping and gate control open new possibilities for potential gate-controlled spintronic THz devices. We find that the carrier concentration and interfacial electric field distribution in the semiconductor films strongly affect the resulting THz emission amplitude. Combining wide-bandgap semiconductor fabrications with spintronic THz devices will offer new solutions to future communication applications such as non-destructive characterization, wireless communication, and quantum computation.