Intrinsic physical properties of flexible van der Waals semiconductor InSe

Abstract

InSe is a van der Waals semiconductor in which mechanical flexibility, high electronic mobility, and non-trivial electronic structures converge, making it an attractive platform for both intriguing fundamental studies and promising device developments. However, the nucleation and growth of phase-pure, intrinsic InSe crystals require stringent thermodynamic conditions, and have therefore remained elusive. Since InSe melts incongruently, the widely used synthesis methods based on cooling of a 1 : 1 In–Se mixture will produce either aggregates of multiphase crystallites or uncontrolled In-rich, heavily electron-doped InSe. This fundamental thermodynamic constraint provides a compelling explanation for the large discrepancies observed in the reported physical properties of InSe. We overcome these limitations by utilizing the travelling solvent floating zone (TSFZ) method to produce high quality, centimeter-size InSe single crystals. Electrical, thermal, and thermoelectric transport measurements demonstrate that TSFZ-InSe single crystals closely approach the intrinsic limit, establishing it as a benchmark material for the future studies of this important material.