Comparison of influence of intercalation and substitution of Cu on electrical and thermoelectric transport properties of InSe alloys

Abstract

Layered post-transition-metal chalcogenides, such as InSe, In₄Se₃, SnSe, and SnSe₂, have recently been investigated as semiconducting electronic materials and thermoelectric materials owing to their adjustable electrical transport properties either by doping or alloying. Herein, the influence of intercalation doping and substitutional doping of Cu in layered InSe alloys on electrical and thermoelectric transport properties was investigated and compared by synthesizing varied compositions of Cu_xInSe and In_1−yCu_ySe. It was found that Cu was intercalated in Cu_xInSe samples (x = 0.01 and 0.02) and behaved as an electron donor, resulting in an increase in the electron concentration and a decrease in the activation energy. Therefore, the power factor of Cu_xInSe samples was increased compared to that of InSe. In contrast, the substituted Cu in the In site of In_1−yCu_ySe samples (y = 0.01 and 0.02) acted as an acceptor, and the power factor decreased owing to a decrease in the electron concentration and activation energy. Moreover, a decrease in thermal conductivity was seen for Cu_xInSe and In_1−yCu_ySe samples due to increased phonon scattering after the addition of Cu. Consequently, an enhanced thermoelectric figure of merit (zT) was only observed for intercalated Cu_xInSe samples due to the increased power factor and decreased thermal conductivity, while substituted In_1−yCu_ySe samples only show degraded zT. A maximum zT value of 0.062 was observed for the Cu_xInSe (x = 0.02) sample at 700 K, which showed a 77% enhancement compared to that of InSe.