New Quantum Photoconductivity and Large Photocurrent Gain by Effective-Mass Filtering in a Forward-Biased Superlatticep−nJunction

We report a new quantum-type photoconductivity in a forward-biased $p^{+}-n$ junction with a superlattice in the $n$ layer. This novel phenomenon is characterized by several striking features: a high photocurrent gain (≃7×${10}^3$), accompanied by a blue shift in the spectral response and a reversal in the direction of the photocurrent, when the forward bias exceeds the built-in potential. Photoconductive gain is caused by the large difference in the tunneling rates of electrons and holes through the superlattice layers, due to their large mass difference (effective-mass filtering). This is the first time that photoconductive gain is observed in a $p-n$ junction.