Thermally induced charged carrier transfer and intersubband transitions in an asymmetrical coupled quantum well structure

We have observed thermally induced charged carrier transfer in an asymmetrical coupled quantum wells structure with energy separation between the first two subbands of the order of the LO phonon energy. In this structure, the population of the second subband is not negligible and intersubband transitions from the second to higher excited subbands can be measured. Due to charged carrier transfer, the built-in dc space charge electric field is changed, giving rise to a blueshift with increasing temperature of the ground to the first excited state intersubband transition. Also, we have found that the measurements of thermally induced intersubband transitions from the second subband provide a direct way to estimate the energy separation between the second subband and the Fermi energy.