Exciton polaritons in double versus single quantum wells: Mechanism for increased luminescence linewidths in double quantum wells

Exciton radiative decay and polaritons in single and double quantum wells are compared and contrasted. Two types of eigenmodes exist in double quantum wells, with the dipole moment in the quantum wells parallel or antiparallel. Energy splittings $\Delta \left({\mathbf{k}}_{\parallel }\right)$ between the two types of modes at small ${\mathbf{k}}_{\parallel })$ are on the order of 0.1 meV for $\frac{\mathrm{GaAs}}{{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}}$-based structures of well width ∼100 Å, which accounts for part of the increased luminescence linewidth in double compared with single quantum wells. Thus the polariton effect gives rise to an intrinsic source of inhomogeneous broadening through $\Delta \left({\mathbf{k}}_{\parallel }\right)$ as well as homogeneous broadening through the radiative width, and both effects are of the same magnitude.