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.