Electrical properties of Pb1−xCdxS epitaxial films

Abstract

We have measured the resistivity ρ and Hall coefficient RH at 300, 77, and 4.2 K of p-type Pb1−XCdXS epitaxial films as a function of substrate temperature Ts, film thickness d, and composition x. The films were vapor deposited on cleaved (111) BaF2 (111) SrF2 , and (001) NaCl and polished (001) BaF2 substrates. The Hall mobility μH at 77 K of p-type PbS films increased approximately linearly from 1 × 104 to 2 × 104 cm2 V−1 sec−1 as Ts was varied from 400 to 500°C, respectively. Both μH and RH increased with d due to the presence of a strong p-type surface layer on the exposed surface. The x of the films was controlled by the x of the source material and Ts. The mole fraction of CdS could be varied between 0.002 < x < 0.06 by varying T between 513 and 410°C, respectively, and using source material with x = 0.06. The electrical properties of samples grown on freshly cleaved (111) BaF2 and (111) SrF2 were essentially identical even though the lattice constant of SrF2 is a better match to Pb1−XCdXS than BaF2. The RH and μH at 77 K were independent of thickness for low substrate temperatures and were observed to increase with increasing thickness for high substrate temperatures. The μH increased with decreasing temperature and became temperature independent below about 30 K, which is similar to the behavior observed in other lead salt compounds. However, the magnitude of μH was considerable lower throughout the 300 to 4.2 K temperature range than for PbS films. The RH showed little temperature variation, which is typical lead salt behavior.