Growth and characterization of large size undoped p-type SnSe single crystal by Horizontal Bridgman method

Abstract

A Horizontal Bridgman (HB) method was employed attempt to grow large size undoped SnSe single crystal. SnSe was crystallized under 2–3 °C/cm temperature gradient and cooled to room temperature at a rate of ∼25 °C/h to release thermal stress. SnSe crystals grown from liquid solution and volatilized vapor were obtained simultaneously. Two single crystals with size about 30 × 20 × 15 mm3 and 35 × 15 × 15 mm3 were peeled off from the liquid growth SnSe, which were reported to be the largest so far. The as-grown SnSe single crystal had standard orthorhombic Pnma space group at room temperature. Stoichiometry ratio of the crystal was measured Sn: Se = 1:1. The density of as-grown crystal is ∼6.16 g/cm3, which is very close to 100% of the theoretical value of SnSe. The obtained SnSe single crystal displayed p-type character with a carrier density of 5.1 × 1017 cm−3 at room temperature. Thermoelectric properties in directions parallel and perpendicular to cleavage bc plane were analyzed, the maximum thermoelectric figure of merit ZT were ZT∥bc = 1.1 and ZT⊥bc = 0.24 near Pnma-Cmcm phase transition temperature.