The properties of strongly localized 1-electron, D0, and 2-electron, D-, donor centers in compound semiconductors were studied by using a theoretical approach which took account of the effect of conduction-band states and interactions with LA and LO phonons. The eigenvalue problem was solved for the ground states of both centers by using the variational method in wave-vector space. An analysis was made of the properties of the D0 and D- donor centers in GaAs under hydrostatic pressures. The calculated energy levels and pressure coefficients agreed with experimental data. Upper and lower bounds were placed on the probabilities of radiative transitions from the extended electron states to the strongly localized D- donor states. A large reduction in these transition probabilities was interpreted in terms of a metastability of the donor centers. It was shown that the metastable behavior of donor centers resulted from a large difference in lattice deformation around the center, which occurred between states of differing electron localization. It was found that the D- center at the substitutional position in GaAs exhibited properties that were characteristic of the DX center. A phonon representation of lattice vibrations was used to calculate the displacements, from equilibrium positions, of ions which surrounded donor centers with differing charge and localization. The results showed that, even for the strongly localized donor state, the deformation of the surrounding lattice involved a large number of ions. The number of ions that effectively contributed to the lattice relaxation energy was estimated to be equal to several thousand.

S.Bednarek, J.Adamowski: Physical Review B, 1998, 57[23], 14729-38