Charge transport in layer semiconductors

Abstract

Electron and hole-drift velocity is measured in the layer semiconductors HgI2, GaSe, PbI2 and GaS, mainly on the direction parallel to the c-axis between 80 and 400 K. In the electric field range in question, electron and hole-drift velocity is proportional to the field except in the case of GaS, where a superohmic behaviour is observed. At 300 K the mobility parallel to the c-axis is μe, = 100 cm2 Vsec, μh = 4 cm2 Vsec for HgI2; μe = 80 cm2 Vsec, μh = 210 cm2 Vsec for GaSe; μe, = 8 cm2 Vsec, μh = 2 cm2 Vsec for PbI2. The highest hole mobility observed in GaS is μh = 80 cm2 Vsec. Where it is possible to compare these data with mobility values perpendicular to the c-axis, the three-dimensional character of the energy bands near the fundamental gap is proved. For HgI2 and GaSe we find no evidence for the large anisotropy of charge-carrier transport properties usually attributed to layered semiconductors. The mobility-temperature dependences found are interpreted on the basis of polar and non-polar optical phonon scattering mechanisms, except in the case of GaS, where a trapping model is used. The effective masses of electrons and holes are reported for PbI2 and, for the first time, for HgI2. © 1976.