Optical transitions of positively charged excitons and biexcitons in single InAs quantum dots

We investigate fine structures observed in the optical transitions of positively charged excitons and biexcitons in single quantum dots. We show that double charged biexciton XX2+ emits into a hot double charged exciton X2+* at first, and then relaxes into charged excitons X2+ or X2+ states via phonon scattering or Auger process respectively. XX2+ gives rise to two elliptically polarized emission lines due to the mixing of two lower-levels in the final state. X2+ causes two optical transitions with different polarizations, i.e., a linearly polarized emission with a fine structure splitting of 45 mu eV and a circularly polarized emission with twofold degeneracy. (C) 2009 American Institute of Physics. [doi:10.1063/1.3262607]