Double two-photon absorption in an asymmetric stepped quantum well in the terahertz range

Abstract

Abstract The electronic states are calculated for the asymmetric AlGaAs/GaAs stepped quantum well. The results show a singular behavior of the energy levels as a function of the step layer's width Lw2. Indeed, we show the existence of plateaus laying within certain Lw2 intervals. Added to the broken selection rules, this offers more frequency modulation of the intersubband transitions. As a major consequence, there is at least one crossing between two different transitions that occurs for many geometries (at specific Lw2 widths), which may enhance the optical properties (absorption and emission) in unipolar based devices. We have, then, performed the calculation of the optical absorption coefficient, in order to evaluate the response of such specific structures to an electromagnetic radiation, especially in the terahertz (THz) domain. The calculations are performed for a particular structure where a double two-photon absorption (TPA) may occur. The first TPA corresponds to the E12 and E24 transitions crossing at 70 meV (17 THz) and the second to the crossing of E23 and E34 transitions at 35 meV (8.5 THz).