EXPERIMENTAL-STUDY OF INTERSUBBAND INFRARED TRANSITIONS IN COUPLED QUANTUM-WELLS UNDER AN ELECTRIC-FIELD

The infrared absorption of a multiple quantum-well structure with coupled wells is studied experimentally. The structure consists of 40 repeats of two coupled quantum wells with a wider doped GaAs well and a narrower undoped GaAs well and AlAs barriers. A strong absorption due to an intersubband transition in the wider wells is seen at about 0.14 eV, which shifts in transition energy when a negative bias is applied and decreases in absorption strength when a positive bias is applied. The shift is due to many-body effects on the transition energy when the electron density in the wider well is reduced, and the decrease is attributed to the blocking of the final state when the upper state in the wider well is populated.