Configuration Interaction in Donor-Acceptor Pairs

The effect of configuration interaction on the electronic states of donor-acceptor pairs in semiconductors is reported. Both the radial and angular dependences of electron- and positive-hole effective-mass functions are varied to minimize the total energy, corresponding to mixing higher $s$ and $p$ states into the eigenstates. The orbits are delocalized and intercore electron and hole densities reduced as a consequence of pairing. A substantial improvement in agreement between theory and experiment is found on including configuration interaction in the calculation of the pair spectra of gallium phosphide. Also, the effect on radiative lifetimes is calculated. The Coulomb overlap, correlation, and anisotropy of the effective masses are also considered, as well as changes in the coupling with the lattice.