Two-electron centers with negative correlation energy in Pb1−x SnxSe solid solutions

Abstract

In Pb{sub 1-x-y}Sn{sub x}Na{sub y}Se solid solutions, the chemical potential F lies lower than the valence-band top E{sub v}, and the dependences F(T) are linear, with the extrapolation to T = 0 K yielding a value E{sub V} - F{sub 0} = (210 {+-} 10) meV for solid solutions containing 0.3 at % of sodium and (250 {+-} 10) meV for those with 0.5 at % of sodium (F{sub 0} is the position of the chemical potential at T = 0 K). The dependences of F{sub 0} on the content of sodium are also linear, with the extrapolation to zero content yielding a value F{sub 0} = 162 {+-} 10 meV for solid solutions containing 2 at % of tin. The correlation energy U of two-electron tin centers in PbSe is independent of the content of tin and sodium and equal to U = (-65 {+-} 10) meV.