Biexcitons and charged excitons in quantum dots: a quantum Monte Carlo study

Binding energies of biexcitons and positively and negatively charged excitons in CuCl/NaCl and GaAs/Al0.3Ga0.7As spherical quantum dots were calculated exactly by the diffusion Monte Carlo method. We have found that binding energy for negatively charged excitons can be larger than that of biexcitons. For small GaAs dots, binding energies of biexcitons and positively charged excitons become negative, because of the difference of quantum confinement between electrons and holes. For quantum dot whose radius is much larger than the effective Bohr radius, the binding energies are reproduced quite well by a simple expression.