Magneto-Optical Studies of the Band Structure of PbS

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By a combination of interband and free-carrier experiments performed on epitaxial and bulk $n$- and $p$-type crystals, the energy-band parameters of PbS in the vicinity of the band edge have been determined at 77\ifmmode^\circ\else\textdegree\fi{}K. Interband magneto-absorption measurements have established that the valence and conduction bands are nondegenerate (except for spin), approximately spherical and parabolic, and have extrema at essentially the same point in k space, probably the $L$ points. Analysis of the data yields values for the energy gap, the reduced effective mass and also the effective $g$ factors for both the valence and conduction bands. Measurements of the Burstein-Moss effect in the zero-field absorption edge indicate multiple bands, most likely at the $〈111〉$ zone boundaries. The individual valence- and conduction-band effective masses were determined from free-carrier Faraday rotation measurements at a temperature slightly above 77\ifmmode^\circ\else\textdegree\fi{}K. Additional structure in the rotation for $p$-type material indicates possible intervalence band transitions. The reversal of the interband Faraday rotation with carrier concentration and temperature is explained on the basis of the band structure determined here. The effects of strain and carrier concentration on the band parameters were also investigated and the effective deformation potential for dilation was determined.