Reduction of carrier mobility in semiconductors caused by charge-charge interactions

We investigate the effect of charge-charge interactions on carrier mobility in titanium dioxide (TiO₂) and silicon (Si) using terahertz spectroscopy. Charge scattering times and plasma frequencies are directly determined as a function of charge density. In Si, a linear increase in scattering rate for densities exceeding 10²¹ m^-3 is attributed to electron-hole scattering. In contrast, in TiO₂, charge-charge interactions are suppressed due to dielectric screening, highlighting the vastly different dielectric properties for these two materials.