Charge-transfer transitions of Fe ions in InP
K. Thonke, Klaus Pressel · Physical review. B, Condensed matter · 1991
We study, in detail, optical transitions of Fe ions in InP. Spectra recorded at different sample temperatures allow reliable assignments of absorption peaks to 3d internal transitions of ${\mathrm{Fe}}^{2+}$. Charge-transfer processes from ${\mathrm{Fe}}^{3+}$ to ${\mathrm{Fe}}^{2+}$ plus a bound hole give rise to multiple absorption bands in the energy range from 6100 to 10 000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. For both the ${\mathrm{Fe}}^{2+}$ ion and the bound hole, a series of excited states are observed. In the ground state of the bound hole, a strong interaction with the d-shell electrons of the ${\mathrm{Fe}}^{2+}$ ion diminishes the spin-orbit coupling to 72% of its original value. By comparison with shallow effective-mass-like acceptor series, the hole binding energy of the ${\mathrm{Fe}}^{2+}$ ion is derived. This allows an exact location of the ${\mathrm{Fe}}^{2+}$ levels in the band gap to be determined.