Ground state energy of the negatively charged exciton X- in bidimensional semiconductors in a steady electric field

The ground state energy of a negatively charged exciton X- (trion) in a bidimensional (2D) semiconductor under a steady parallel electric field has been calculated variationally for different values of the electron to hole effective mass ratio. It is found that the binding energy W, defined as the difference between the trion and exciton energies, increases with a weak electric field. The results are compared with those we have previously obtained in bulk (3D) semiconductors. It is shown that charged excitons bound states can exist in 2D semiconductors for larger values of the field than in the 3D case. It is also found that the ratio W-2D/W-3D decreases at increasing fields for all values of the mass ratio. The quantization of the center of mass motion gives rise to Wannier-Stark levels. (C) 1997 Elsevier Science Ltd.