Investigation of conduction band structure, electron scattering mechanisms and phase transitions in indium selenide by means of transport measurements under pressure

摘要

In this work we report on Hall effect, resistivity and thermopowermeasurements in n-type indium selenide at room temperature under eitherhydrostatic and quasi-hydrostatic pressure. Up to 40 kbar (= 4 GPa), thedecrease of carrier concentration as the pressure increases is explainedthrough the existence of a subsidiary minimum in the conduction band. Thisminimum shifts towards lower energies under pressure, with a pressurecoefficient of about -105 meV/GPa, and its related impurity level trapselectrons as it reaches the band gap and approaches the Fermi level. Thepressure value at which the electron trapping starts is shown to depend on theelectron concentration at ambient pressure and the dimensionality of theelectron gas. At low pressures the electron mobility increases under pressurefor both 3D and 2D electrons, the increase rate being higher for 2D electrons,which is shown to be coherent with previous scattering mechanisms models. Thephase transition from the semiconductor layered phase to the metallic sodiumcloride phase is observed as a drop in resistivity around 105 kbar, but above40 kbar a sharp nonreversible increase of the carrier concentration isobserved, which is attributed to the formation of donor defects as precursorsof the phase transition.