ROW OF DEFECTS IN ACCEPTOR DOPING OF PBTE-TYPE SEMICONDUCTORS WITH GROUP I ELEMENTS

The temperature and impurity-concentration dependences were obtained of the Hall coefficient, thermoelectric power, and electrical resistivity of sodium-doped dilute Pb1-xSnxTe (x = 0.005 and 0.0 1) solid solutions. The existence of two doping ranges was established: the electrically active doping (0-1 at. % Na) and the range of stabilization of the Hall density of carriers (1-2.2 at. % Na). In the latter case the rise of the Hall coefficient with temperature became weaker on increase in the Na content and it disappeared almost completely at the highest dopant concentration. Moreover, this range was characterized by an increase in the thermoelectric power and a stronger scattering of holes at T below 400 K. The Mossbauer method was used to show that the tin impurity atoms did not influence directly this behavior of the properties of the heavily doped samples. The experimental data were interpreted on the basis of a model relating the pinning of the Fermi level in the doped Pb(Sn)Te alloys to a modification of the intrinsic defects that were formed under the influence of heterovalent replacement of Pb with sodium. The isovalent Sn impurity created conditions favorable for this process. An analysis was made of the transformation of a metal vacancy into an antisite Te atom and of the resultant changes in the spectrum of quasilocal states.