Theory of Trion Spectra in Semiconductor Nanostructures

A consistent density-matrix approach for the absorption spectra of semiconductor nanostructures at finite carrier densities is presented that describes both bound and scattering three-particle states (trions). It automatically includes the two-particle bound states (excitons). In optical transitions, the initial electron or hole momentum is transferred to the final trion state, which — due to recoil energy — gives rise to low-energy tails at the trion and exciton line. A high-energy tail at the exciton is due to the exciton–electron scattering states (trion continuum). The incomplete transfer of exciton oscillator strength to the main trion line and the trion continuum is exemplified by a quantum wire calculation.