Raman spectroscopy of impurity states in gallium-doped PbTe

We present Raman spectra and results of galvanomagnetic measurements of PbT e single crystals, doped with gallium, between 10 and 300 K. The effect of persistent photoconductivity depends on the gallium concentration. In all s amples well-resolved peaks were observed at about 104 cm(-1) (impurity-indu ced PbTe LO mode) and 166 cm(-1) at all temperatures. Another mode appears at about 117 cm(-1) at temperature below 250 K. One additional mode, at abo ut 188 cm(-1), is observed in PbTe + 0.4 at% Ga. These modes are discussed in terms of local vibrations of impurities corresponding to different Ga ch arge states.