FAR-INFRARED SPECTROSCOPY OF LOCALIZED STATES IN INDIUM-DOPED PBTE AND PB(1-X)A(X)TE (A(X)=MN-0.017 SN-0.18) ALLOYS

Far-infrared reflection spectra of indium doped PbTe single crystal as well as of Pb(1-x)A(x)Te alloys (A(x) = Mn-0.017; Sn-0.18) in the tem perature range between 10 and 300 K are presented. Analysis of the spe ctra was made by a fitting procedure based on the model of coupled osc illators. At temperatures below T = 200 K, two additional modes appear , along with the modes which describe strong plasmon-LO phonon couplin g. The first mode, at about 122 cm(-1), is a local impurity mode of in dium which represents a population of metastable states due to the tra nsfer of electrons from two-electron to one-electron metastable impuri ty states. The second mode at about 488 cm(-1) we believe to appear as a consequence of the electron transfer from a stable impurity two-ele ctron state to the conduction band.