Hall Coefficient Behavior and the Second Valence Band in Lead Telluride

Abstract

Measurements of the temperature dependence of the Hall coefficient are presented for samples of p‐type PbTe having carrier concentrations between 3×10¹⁷ and 1×10²⁰ cm⁻³. As the temperature increases, the Hall coefficient for any given carrier concentration at first remains at the constant value R_L and then increases steadily at higher temperatures. As the carrier concentration increases from the lowest to the highest values studied, the Hall ratio R_295°/R_L increases smoothly from about 1.1 to 2.5. The data are analyzed in terms of a simple two‐valence‐band model. The results indicate that the energy separation between the two band edges is about 0.14 eV at 0°K, and that carriers in the second band have a heavy mass and low mobility relative to those in the first. The data also suggest that there are no carriers in the second band in the liquid‐helium temperature range, even at the highest carrier concentration. This requires that the first valence band be strongly nonparabolic.