Nonequilibrium evaporation enables carrier polarity control in Bi‐Te thin films

Abstract

Carrier polarity is a fundamental parameter that defines the electronic functionality of semiconductors. In multielement chalcogenides grown far from equilibrium, the deposited phase can deviate substantially from the nominal source material, providing an alternative route for polarity selection beyond conventional doping and defect control. Here, we show that carrier polarity in thermally evaporated Bi–Te thin films is governed by nonequilibrium compositional fractionation along the evaporation pathway. At the initial stage of deposition, preferential Te incorporation produces an amorphous, strongly Te‐rich phase with robust p‐type transport and high hole concentration. With continued growth, the deposited phase progressively evolves toward Bi ₂ Te ₃ ‐rich crystalline Bi–Te films, accompanied by the recovery of conventional n‐type behavior. This polarity crossover does not originate from an intrinsic amorphous‐to‐crystalline inversion of Bi ₂ Te ₃ but from a growth‐induced transition in the dominant conducting phase. These results identify nonequilibrium compositional fractionation as a mechanism for controlling carrier polarity in Bi–Te chalcogenides and demonstrate a route to generate distinct p‐ and n‐type transport regimes within a single material system without external doping.