The nature of dielectric state and self compensation mechanisms in PbTe doped with Ga

Abstract

The long-standing problem of impurity states in narrow-gap PbTe crystals doped with group-III element Ga was analized by means of density functional theory. We focus on the mechanisms of the self-compensation during growth as well as during post-growth annealing to clarify the mechanism of dielectric state formation necessary for the device fabrication. The unique feature of the presented work is consideration of the simplest impurity complex as well as of a lead vacancy , gallium substituting for Pb site and interstitial gallium in various charge states. Calculations show that complex has the lowest formation energy among other gallium-related defects and is a double donor. is a single donor while is amphoteric impurity which act as a donor or acceptor depending on the Fermi level position. Moreover, we conclude that neutral impurity is metastable due to the self-compensation and formation of complex with simultaneous creation of . Calculated binding energy of this complex suggests that it is stable for the actual temperatures and concentrations. In addition the defect is responsible for spontaneous creation of lead vacancy which prevents an increasing of the carrier concentration. Therefore, the considered complex determines the most striking features of PbTe crystals doped with Ga, namely DX-like properties and dielectric state formation. This defect plays a crucial role in real crystals and clarifies the nature of properties important for device fabrication.