Sequential versus coherent tunneling in double-barrier diodes investigated by differential absorption spectroscopy

We have used differential absorption spectroscopy to measure charge distributions in the quantum wells of several double-barrier diodes. We find that the ratio of the stored charge to the current is not equal to the coherent-state lifetime and is basically insensitive to the amount of scattering. We experimentally demonstrate that phase-breaking collisions take place in our structures by observing the energy distribution of the stored charge in both single- and double-resonance structures.