Imaging Carrier Dynamics on the Surface of the N-type Silicon

The nonequilibrium dynamics of carriers in semiconductors plays a major role in the performance and efficiency of the electronic and photovoltaic devices. In this study, we use the scanning ultrafast electron microscopy (SUEM) technique to study the surface photovoltage dynamics in doped silicon samples. We observe that the optical excitation of lightly doped n-type and p-type silicon as well as heavily doped n-type silicon increases the electron density on the surface. In contrast, the optical excitation of heavily doped p-type silicon increases the hole density on the surface. Furthermore, we show that the rise and the decay timescales of these events strongly depend on the doping concentration.