Influence of donor-triad molecules on the optical properties of semiconductors

The dielectric constants and the refractive index of n-type GaAs are obtained by a second-order many-body-perturbation-theory calculation of the transition energy of the donor-triad molecules. The imaginary part of the dielectric constant, which is associated with the optical conductivity, exhibits a peak at an energy in relatively good agreement with the observed line ‘‘X.’’ This result supports the interpretation of this peak as due to the electronic ${\mathrm{H}}_3$→${\mathrm{H}}_3^{+}$ transition from their impurity ground state.