Summary
We have shown a concept which makes use of two main effects common to all nipi-structures: the lifetime
enhancement and the sensitivity of the potential modulation to screening by excess carriers. Even if no absorption
below band gap is possible, such as in long period nipi's, this type of structures remains interesting for photon
detection. If we combine the huge lifetime enhancement which depends on the potential modulation and the
enhanced ambipolar diffusion of excess carriers resulting from the sensitivity of the potential to additional carriers,
we get new mechanisms for gaining and controlling the detector response. The use of a lateral current which is
supplied selectively to the embedded n-layer causes a lateral voltage drop which leads to non linear I(V)-curves
with well defined current plateaus. These current plateaus shift with increasing illumination intensities. On the
other hand the lateral voltage drop leads to an increase of the potential modulation near the positive contact and a
decrease near the negative contact. Therefore the areas where generation and recombination dominate are separated
from each other and the excess carriers are transferred very fast between these regions. The decrease of the potential
modulation near the negative contact can be controlled by the external lateral current in order to speed up the
detector response. This general concept which is not limited to a special host material was tested experimentally by
use of PbTe p-n-p structures exhibiting good agreement with the simulations based on the presented theoretical
model.