Evidence for a negative interband photoconductivity in arrays of $\mathrm{Ge}/\mathrm{Si}$ type-II quantum dots

We find that conductivity of stacked arrays of $\mathrm{Ge}/n-\mathrm{Si}$ quantum dots decreases under interband optical excitation. The negative photoeffect is explained by trapping the mobile electrons in the quantum wells created by the Hartree potential of holes photoexcited in the dots. A phenomenological theory of the effect is fitted to the data. The obtained electron trap energy, $\sim 17\hspace{0.5em}\mathrm{meV},$ is consistent with the results of self-consistent calculations.