Intersubband transitions in $\mathrm{Zn}\mathrm{O}$ material systems are predicted to be promising candidates for infrared and terahertz (THz) optoelectronic devices due to their unusual material properties. In particular, the temperature performance of THz quantum cascade lasers is postulated to be significantly enhanced using $\mathrm{Zn}\mathrm{O}$ material systems due to their large optical phonon energy. Taking a step forward toward that goal, intersubband transitions in $\mathrm{Zn}\mathrm{O}/{\mathrm{Mg}}_{x}Z{\mathrm{n}}_{1-x}\mathrm{O}$ asymmetric coupled quantum wells are observed on a nonpolar m plane $\mathrm{Zn}\mathrm{O}$ substrate. Two absorption peaks are observed in the energy range from approximately 250 meV to approximately 410 meV at room temperature, unambiguously demonstrating the interwell coupling in the asymmetric coupled quantum wells. A theoretical model taking into account the interaction between intersubband transitions shows reasonable overall agreement with the experimental results, thus proving the strong coupling nature of the investigated system. As the building block of complex quantum structures based on intersubband transitions, the results presented show great potential applications of $\mathrm{Zn}\mathrm{O}/{\mathrm{Mg}}_{x}Z{\mathrm{n}}_{1-x}\mathrm{O}$ material systems in infrared and THz optoelectronics and physics.

• Received 22 July 2019
• Revised 13 September 2019

DOI:https://doi.org/10.1103/PhysRevApplied.12.054007

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society