Negative differential photoconductance in an alternatively doped multi-quantum well structure.

We have measured the infrared photoconductivity of an alternatively doped multi-quantum well structure. From this measurement, the density of the electrons dynamically stored in the undoped wells, which is critically important in the theory of tunneling, can be deduced at different external biases. The result is fully consistent with the theory of sequential tunneling. In the photoresponse, a striking negative differential photoconductance feature is observed. This observation indicates that a high speed infrared light modulator can be made using a similar device structure.