The hall effect in liquid semiconductors

The proper interpretation of the Hall coefficient R_H of liquid semiconductors is still an unsolved problem, and it is a particularly interesting one in view of the frequently observed discrepancy in sign with the Seebeck coefficient. We present some new data which include measurements of the Hall mobility μ_H in liquid thallium-tellurium through the composition range where the Seebeck coefficient S changes sign, and in the range where S is negative. An abrupt change in magnitude of μ_H occurs at the intrinsic composition (Tl₂Te, where S changes sign), and μ_H is observed to have an appreciable dependence on temperature only at this composition. This is consistent with transport by carriers in two bands. μ_H is lower on the Tl-rich side of Tl₂Te, and the formula n_H = 1/R_He yields a value for n_H which is ten times larger than the electron concentration inferred from the composition, assuming that electrons are derived from the Tl in excess of Tl₂Te. We review the various suggested interpretations of the Hall effect in liquid semiconductors from several points of view, and conclude that the conventional formula n = ± 1/R_He is unreliable for inferring either the sign or concentration of the carriers.