Ambipolar drift of spatially separated electrons and holes - art. no. 085307

We report on the ambipolar transport process of photogenerated, spatially s eparated charge carriers in the doping layers of a p-i-n diode under the in fluence of lateral electric fields. By including externally applied electri c fields into the theory of ambipolar diffusion of spatially separated elec trons and holes, we show that the transport of excess carriers can be descr ibed as a combined drift and diffusion process. Compared to the well-known ambipolar transport in bulk material, the ambipolar diffusion process is en hanced by several orders of magnitude, whereas the ambipolar drift can be d escribed by the same ambipolar mobility as in bulk material if the electric fields in both doping layers are identical. One major difference of the am bipolar drift of electrons and holes propagating in different layers in com parison to bulk material is the possibility to control the ambipolar mobili ty dynamically by changing the dark carrier densities by varying the revers e bias applied to the p-i-n structure. Most interesting however, is the fac t that the ambipolar drift can be controlled by different external fields f or electrons and holes. In order to verify the predictions of our theoretic al description of the ambipolar transport of spatially separated electrons and holes, we have developed a new pump-and-probe technique that allows for a direct temporally and spatially resolved investigation of the various tr ansport scenarios. The results agree very well with the theoretical simulat ions.