Exciton states in coupled double quantum wells in a static electric field

We calculate variationally the four lowest energy levels and oscillator strengths of 1s excitons in a coupled-double-quantum-well structure in an applied static electric field. We demonstrate the importance of employing a variational wave function, which allows for single-particle-state mixing, and which treats the in-plane radial dependence of the exciton states in a more sophisticated manner than the commonly used single exponential. We accomplish this by expanding the eigenstates in a basis consisting of exciton wave functions rather than the commonly used basis of free electron and hole wave functions. These basis wave functions are the ground states of the excitonic Hamiltonians where the electron is primarily confined to one layer and the hole to another—possibly the same—layer. We apply this method to symmetric coupled wells as well as to an asymmetric structure in which the electron and hole in the ground state are localized in separate layers even in the absence of an applied electric field. From an analysis of our results, we arrive at a general approach to qualitatively understand and classify the excitonic properties of these structures.