Chemical Tuning of Carrier Type and Concentration in a Homologous Series of Crystalline Chalcogenides

Abstract

Tellurium-based phase-change materials (PCMs) enable applications from optical and electronic data storage to thermoelectrics and plasmonics, which all demand precise control of electronic properties. These materials contain an unusually large number of vacancies: "stoichiometric" ones that stem from the chemical composition and "excess" vacancies that act like classical dopants. Here we show how both types of vacancies can be controlled independently in the solid solution Sn(Sb 1−x Bi x ) 2 Te 4 . We vary x in small steps over the entire compositional range and show that this has a profound effect on the material's electronic nature: remarkably, we observe a change from p-to n-type conduction at x ≈ 0.7, solely controlled by composition. Our findings lead to a new compositionally (that is, chemically) tunable materials platform that enables precise control of electrical properties.

Exploring the subsurface atomic structure of the epitaxially grown phase-change material Ge2Sb2Te5

“…Moreover, it is known that the epitaxial films are strongly p-type doped [35] with an unintentionally varying charge carrier density p = (0.1-3) × 10 26 m −3 [24,26]. This doping is typically related to excess vacancies [36][37][38]. The epitaxial films also exhibit a significantly improved mobility μ with respect to polycrystalline films prepared by magnetron sputtering, i.e., an increase of μ by more than an order of magnitude [24,26,39].…”

Disorder Control in Crystalline GeSb2Te4 and its Impact on Characteristic Length Scales

“…This already pointed to a prominent role of disorder. The number of charge carriers, on the contrary, was rather firmly linked to the number of (excess) vacancies, but hardly changed during annealing, thus not contributing significantly to the conductivity trend.…”

Materials Screening for Disorder‐Controlled Chalcogenide Crystals for Phase‐Change Memory Applications

“…Anderson localization in vacancy‐rich compounds was already investigated by Cutler and Mott in 1969, who showed that in Ce 2 S 3 , the random distribution of vacancies creates a tail of localized states in the conduction band, and that addition of a small number of cerium atoms per formula unit leads to a small number of electrons in the tail of the band and, thus, to insulating behavior. [ 31 ] More recently, Anderson localization effects were observed in rocksalt‐like compounds chemically related to the abovementioned PCMs, including SnBi 2 Te 4 and SnSb 2 Te 4 thin films, [ 32,33 ] and also in GeTe nanowires. [ 34 ] In ref.…”