Ultrafast dynamics of photoinduced terahertz electron-hole plasma waves in semiconductor junctions

The ultrafast transport processes of electrons and holes excited by femtosecond laser pulses are essential for a better understanding of carrier dynamics in semiconductors. Transient optical techniques are commonly used to investigate the carrier excitation and transport in these materials. Recently, ultrafast scanning electron microscopy has been employed to elucidate the ballistic dynamics of such hot carriers near a $p\text{\ensuremath{-}}n$ junction. We provide here a model not only to explain the previously reported superfast expansion of electron-hole clouds but also to predict plasma wave behavior at high laser fluences. In addition to a bipolar junction, we also investigate the well structure of a $p\text{\ensuremath{-}}n\text{\ensuremath{-}}p$ junction sandwiched by insulating layers. By confining hot carriers inside junctions, these carriers begin to oscillate as a result of Coulomb interactions among carriers and with the intrinsic field at the depletion zone, leading to the occurrence of terahertz-scale plasma waves for potential applications as pulsed terahertz light sources.