Large Single‐Crystalline n ‐Type SnS Flakes by Vapor Transport Growth With In Situ Bi Doping

Doping is a primary design parameter in semiconductor devices. Whereas traditional materials, such as Si, Ge, and GaAs, benefit from facile ambipolar substitutional doping by shallow donors and acceptors, many compound semiconductors are strongly auto‐doped by native point defects. Layered Sn monochalcogenides, for example, show ubiquitous p ‐type conduction due to Sn vacancy defects with low formation energy. Realization of robust n ‐type doping would support numerous applications, e.g., in energy conversion as well as conventional and neuromorphic computing. Here, we demonstrate n ‐type doping of large single‐crystalline SnS flakes by substitutional incorporation of Bi. Optical and electron microscopy show well‐formed SnS:Bi flakes. X‐ray photoelectron spectroscopy confirms the controllable incorporation of Bi in two oxidation states, corresponding to ionized substitutional donors as well as non‐ionized impurities that fill Sn vacancies and thus suppress p ‐type conduction. Field‐effect transport and Hall effect confirm electrons as majority carriers with mobility exceeding 110 cm ² /V s. Crystallization of thin SnS:Bi flakes in a distorted ferroelectric phase with stripe domains, similar to undoped SnS flakes, implies that ambipolar doping can be combined with in‐plane ferroelectricity in support of emerging applications of this versatile van der Waals semiconductor.