Vapor-crystal equilibrium and electrical properties of HgTe

Abstract

The vapor-crystal equilibrium of HgTe has been investigated by measuring the electrical properties of samples which were quenched after having been annealed at 150–550°C long enough to reach equilibrium with either (1) a liquid Hg reservoir, (2) a two-phase Hg-rich or Te-rich ingot, or (3) internal Te-rich microprecipitates. Except in a few cases, the electrical measurements showed conclusively that the samples were p-type. Hall coefficient measurements at 4·2°K and about 100 kG could be used to determine the value of ( p − n) for samples with ( p − n) exceeding 4 × 10 18cm −3. Less p-type samples could be arranged in order of ( p − n) by comparing their values of the Seebeck coefficient at 300°K and the low-field Hall coefficients at 300 and 77°K. For samples annealed at 550°C, ( p − n) increases monotonically with decreasing Hg pressure from 4·7 × 10 18cm −3 for Hg saturation to about 9 × 10 18 cm −3 for Te saturation. Independent of any microscopic model, this variation shows that ( p − n) increases monotonically with increasing Te content. According to the simplest microscopic model, the predominant point defects are Hg-vaeancy or Te-interstitial acceptors, and above 450°C the entire homogeneity range lies on the Te-rich side of the stoichiometric composition. Along both the Te-rich and Hg-rich solidus lines the Te content increases with increasing temperature. The value of ( p − n) extrapolated to the maximum melting point is about 1·5 × 10 19 cm −3.