Intersubband Transition in Asymmetric Quantum Well Infrared Photodetector

Intersubband transition in perfect rectangular quantum well is known to be limited by “selection rule” that results from certain symmetries of wavefunctions. This letter presents Green´s function-based analysis that incorporates energy state broadening due to optical absorption and shows how stepped quantum well can introduce required “asymmetry” to defy the selection rule by breaking the bound state wavefunction symmetry and thus improve the overall optical absorption. Calculation for Al_xGa_1-xAs/GaAs/In_yGa_1-yAs stepped quantum well confirms that coupling among certain energy states increases with asymmetry and, as a result, so does the magnitude of optical absorption. The simulation approach presented is simple, physically intuitive, and extendable to any arbitrary shaped asymmetric quantum well.