S. Bednarek et J. Adamowski, METASTABILITY AND LATTICE-RELAXATION FOR D-0 AND D- DONOR CENTERS, Physical review. B, Condensed matter, 57(23), 1998, pp. 14729-14738
Properties of strongly localized one-electron (D-0) and two-electron (
D-) donor centers in semiconducting compounds are studied with the hel
p of the theoretical approach, which takes into account the influence
of the conduction-band states and interactions with LA and LO phonons.
The eigenvalue problem has been solved for the ground states of both
the centers by the variational method in the wave-vector space. The de
scription is given of the properties of the D-0 and D- donor centers i
n GaAs under hydrostatic pressure. The calculated energy levels and pr
essure coefficients agree with the experimental results. Upper and low
er bounds have been obtained for probabilities of radiative transition
s from the extended electron states to the strongly localized D- donor
states. A large reduction received for these transition probabilities
has been interpreted in terms of metastability of the donor centers.
It is shown that the metastable behavior of donor centers results from
a large difference in a lattice deformation around the center, which
occurs between the states of different electron localization. It is fo
und that the D- center at the substitutional position in GaAs exhibits
the properties that are characteristic for the DX center. The phonon
representation of lattice vibrations has been applied to calculate the
displacements from equilibrium positions of the ions surrounding the
donor centers of different charge and localization. The results show t
hat-even for the strongly localized donor state-the surrounding-lattic
e deformation encompasses a large number of ions. The number of ions t
hat essentially contribute to the lattice relaxation energy is estimat
ed to be several thousand. The present work takes into account the lon
g-range component of the lattice deformation induced by the presence o
f the impurity in a crystal.