Epitaxial tin selenide thin film thermoelectrics

[Display omitted] •In-plane epitaxial relation with DyScO3 substrate causes the formation of two SnSe domain types.•One SnSe domain aligns with substrate, while second SnSe domain aligns off-axis by 7 ∼ 8°.•In-plane electrical conductivity along the SnSe (b,c)-plane shows an abrupt increase above 400 K.•Epitaxial SnSe film exhibits a maximum power factor of about 6.0 μW·K−2·cm−1.•A typical low thermal conductivity would result in an in-plane ZT value of about 1.55 at 775 K. To enable the realization of miniaturized thermoelectric energy generation (TEG) devices for autonomous wireless sensors, high-quality thin film architectures are required. Although tin selenide (SnSe) has been identified as a promising thermoelectric material exhibiting ZT values up to 2.6 at 923 K for single crystals, most thin film studies evaluated polycrystalline or textured SnSe samples. Here, we have explored for the first time the impact of epitaxial alignment of the orthorhombic SnSe crystal structure on an orthorhombic DyScO3 substrate, in strong contrast to the few previous studies on cubic substrates. The achieved (100)-oriented single crystalline SnSe thin films exhibit the formation of two SnSe domain types. The in-plane electrical conductivity along the (b,c)-plane shows an abrupt increase above 400 K instead of the typical steady increase. The in-plane Seebeck coefficients exhibit very similar values as single crystals, leading to a maximum power factor of about 6.0 μW·K−2·cm−1. For these SnSe thin films, exhibiting two domain variants with in-plane alignment of the (b,c)-plane, a typical low thermal conductivity is expected, demonstrating the effectiveness of epitaxial alignment to enhance thermoelectric performance and to enable the realization of miniaturized thermoelectric energy generation (TEG) devices for autonomous wireless sensors.