Long intrinsic radiative lifetimes of excitons in quantum wires

Calculations of exciton radiative lifetimes in quantum wires free of defects are presented. Only excitons near zero wave number can spontaneously undergo radiative decay while conserving energy and momentum. The lifetime of the lowest-energy exciton in 100-Å-diam GaAs quantum wires, ${\mathrm{\tau }}_{\mathrm{spon}}$=150 ps, is an order of magnitude longer than in quantum wells. This is due to the finite spatial coherence in the lateral direction. Thermalization effects lead to an effective lifetime of τ(T)=140 √T ps ${\mathrm{K}}^{\mathrm{-}1/2}$.