Behavior of the Fe impurity in Hg$_3$In$_2$Te$_6$

Optical and photoelectric measurements reveal that doping with iron leads to the formation of a deep level at $E_c$ – 0.69 eV in Hg$_3$In$_2$Te$_6$ crystals. When light is absorbed by Fe$^{2+}$ impurity centers, both electronic transitions of the impurity-level–conduction-band type and optical transitions between ground and excited states of the aforementioned centers (intracenter transitions) are observed. Investigations of transport phenomena point to the acceptor properties of Fe$^{2+}$ centers.