INFRARED TRANSMISSION AND PHOTOCURRENT STUDY OF INTERSUBBAND TRANSITIONS IN A COUPLED ASYMMETRICAL QUANTUM-WELL STRUCTURE

We report the results of an experimental study of intersubband transitions in a coupled asymmetrical double quantum well structure. Infrared transmission and photocurrent spectra are measured at 80 K. One period of the 40-repeat quantum well structure consists of a wide Si-doped GaAs well and a narrow undoped GaAs well separated by a thin AlGaAs barrier. The intersubband transition in the wide well occurs at about 9.5-mu-m, and, under appropriate bias, an intersubband absorption feature in the narrow well appears at 6.2-mu-m. The switching between intersubband transitions at 9.5 and 6.2-mu-m relies on electron transfer between the wells. Our absorption measurements provide direct evidence that up to 35% of the 9.2 x 10(11) cm-2 electrons in the wide well can be transferred into the narrow well. These transferred electrons give rise to a photocurrent peaked at 6.2-mu-m.