On the origin of p-type conductivity in BaCuChF (Ch = S, Se Te)

Density functional calculations have been performed to
elucidate the source of unintentional p-type conductivity in nominally
stoichiometric BaCuChF (Ch = S, Se, Te) wide bandgap semiconductors. Formation
enthalpies and transition levels (activation energies) were found for all
vacancies and antisites, and for some interstitials. Results of this initial
study suggest that of all hole-producing point defects, copper vacancies are
the easiest to form. The formation energy of copper vacancies decreases with increasing
mass of the chalcogen atom in BaCuChF. This trend agrees with
temperature-dependent resistivity measurements on BaCuChF thin films and
pressed pellets, which show that conductivity is highest in nominally undoped
materials for BaCuTeF and lowest for BaCuSF. These and other trends indicate
that copper vacancies are responsible for unintentional p-type conductivity in
these materials.