Doping of PbTe with Group-III elements: An ionic lattice approach

It is shown that donor or acceptor behavior for a Group-III element in PbTe depends on the balance between the energy needed to promote the $s$-level electrons of the element above the top of the valence band of the host crystal (donor action) and the lattice energy gained as a result of the increased charge and smaller radius of the impurity. The lattice energy for the element in its donor and acceptor state is calculated on the basis of an ionic host-lattice model which enables one to take into account lattice distortions. The calculations predict that Tl and Ga should act as acceptors and In and Al as donors. They also predict that, with the exception of Al, the major fraction of these elements will remain electrically inactive.