Electronic Structure of PbS, PbSe, and PbTe

Lead salts are ionic semiconductors with many properties in common. Their IV-VI electron configuration is relatively unusual, and appears to be reflected in the interesting phonon and dielectric properties they share. Among these are low values of the TO phonon frequency at Γ and high static dielectric constants. It is clear that the electronic structures of PbS, PbSe, and PbTe are much the same, with all three lead salts exhibiting a direct minimum energy gap E 0 at the L point. The surfaces of constant energy for both electrons and holes are ellipsoidal near the band edges, but approach a cylinder-like shape farther from the L point. The conduction and valence bands in all the lead salts are definitely nonparabolic, displaying a concomitant dependence of the effective mass on carrier concentration. Based primarily on studies of PbTe, a two-valence band model is well supported by experiment. The order of higher energy bands appears quite well established, and reliable values of the energies of several interband transitions have been obtained.