INVESTIGATION OF CONDUCTION-BAND STRUCTURE, ELECTRON-SCATTERING MECHANISMS, AND PHASE-TRANSITIONS IN INDIUM SELENIDE BY MEANS OF TRANSPORT MEASUREMENTS UNDER PRESSURE

In this work we report on Hall-effect, resistivity, and thermopower me asurements in n-type indium selenide at room temperature under either hydrostatic or quasihydrostatic pressure. Up to 40 kbar (=4 GPa), the decrease of carrier concentration as the pressure increases is explain ed through the existence of a subsidiary minimum in the conduction ban d. This minimum shifts towards lower energies under pressure, with a p ressure coefficient of about -98 meV/GPa, and its related impurity lev el traps electrons as it reaches the band gap and approaches the Fermi level. The pressure value at which the electron trapping starts is sh own to depend on the electron concentration at ambient pressure and th e dimensionality of the electron gas. At low pressures the electron mo bility increases under pressure for both three- and two-dimensional el ectrons, the increase rate being higher for two-dimensional electrons, which is shown to be coherent with previous scattering mechanisms mod els. The phase transition from the semiconductor layered phase to the metallic sodium chloride phase is observed as a drop in resistivity ar ound 105 kbar, but above 40 kbar a sharp nonreversible increase of the carrier concentration is observed, which is attributed to the formati on of donor defects as precursors of the phase transition.