The influence of subwavelength geometry on extracting the electrical properties of semiconductors by terahertz spectroscopy

Terahertz (THz) spectroscopy is a non-contact technique well-suited for probing the ultrafast electrical conductivity of semiconductor nanostructures, where conventional methods are often impractical. However, geometric resonances in these nanostructures can distort the measured THz response, complicating the extraction of the intrinsic material properties. Here, we use THz spectroscopy to study GaAs nanowires of varying lengths and observe that the resonant frequency increases as the nanowire length decreases. Further measurements on a model system of well-defined GaAs microsquares (ranging in size from 500 × 500 to 7 × 7 μm²) confirmed the relationship between structure size and resonant frequency. We verify that a plasmon-based model successfully separates the geometric response from the intrinsic charge-carrier response. Thus, the model allows for the accurate evaluation of critical material properties in nanostructured semiconductors, such as electron mobility. Fluence-dependent measurements and finite-difference time-domain simulations confirm the plasmonic nature of the resonances.