Investigation of an amphoteric behaviour of arsenic dopant in polycrystalline SnSe

Abstract

We investigated eventual amphoteric behaviour of As atoms in SnSe by substituting in either cation or anion site. The investigation involved two series of polycrystalline samples of nominal composition Sn1-xAsxSe (0 ≤ x ≤ 0.1) and SnAsxSe1-x (0 ≤ x ≤ 0.08). The prepared powders were identified by X-ray diffraction. Hot-pressed from powder, polycrystalline pellets were used for characterization of transport and thermoelectric properties in temperature range of 300–730 K. An embedding of the As atoms in either cation or anion site seems to prevent formation of the major defects present in the undoped SnSe, tin vacancies VSn2-. Instead, selenium vacancies VSe2+ together with substitutional defects AsSn+ play the major role in the electronic transport in the Sn1-xAsxSe system. Due to rather low solubility of arsenic in the system (x ≤ 0.02), either As inclusions or amorphous As-Se phase is formed in highly doped samples. In the case of SnAsxSe1-x, As atoms enter Se position forming AsSe-, which increases the hole concentration in the doped samples at lower temperatures. At higher temperatures, the properties of the compounds (for x ≤ 0.03) are influenced by the formation of highly conductive AsSn phase. Generally, the substitution of As for both anion and cation lead to no evident enhancement of the thermoelectric figure of merit ZT.