Infrared transmission and photocurrent study of intersubband transitions in a coupled asymmetrical quantum well structure

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Abstract
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 μm, and, under appropriate bias, an intersubband absorption feature in the narrow well appears at 6.2 μm. The switching between intersubband transitions at 9.5 and 6.2 μm relies on electron transfer between the wells. Our absorption measurements provide direct evidence that up to 35% of the 9.2×1011 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 μm.