Electronic structure of ${\mathrm{Ni}}^{+}$ in ${\mathrm{I}}_B-\mathrm{I}\mathrm{I}\mathrm{I}-{\mathrm{VI}}_2$ chalcopyrite semiconductors

Electron-spin-resonance (ESR) and optical-absorption spectra of ${\mathrm{Ni}}^{+} \left(3\mathrm{}{d}^9\right)$ impurities have been observed in the ternary chalcopyrite compounds CuAl${\mathrm{S}}_2$, CuGa${\mathrm{S}}_2$, and AgGa${\mathrm{S}}_2$. Identification of the axial ESR centers as being due to Ni has been confirmed by the observation of hyperfine structure in crystals enriched with ${}_{}{}^{61}{}_{}{}^{}\mathrm{Ni}$. Large axial-field splittings due to the tetragonal crystal-field component in the chalcopyrite structure are inferred from the ESR and optical data. All experimental results can be consistently interpreted within the framework of static crystal-field theory. A complete set of crystal-field parameters is obtained for ${\mathrm{Ni}}^{+}$ in each of the three hosts. No evidence for a Jahn-Teller effect is found.