Improved thermoelectric power factor achieved by energy filtering in ZnO:Mg/ZnO hetero-structures

•The ZnO base layer improves zno:Mg crystallinity of glass/ZnO/ZnO:Mg film.•The bilayer tunes the carrier mobility and seebeck coefficient.•Its power factor (~ 253.5 μW.m − 1K − 2) is higher than that of zno:Mg single layer (~ 48.1 μW.m − 1K − 2) . ZnO:Mg(5 at%)/glass and ZnO:Mg/ZnO/glass thin films with a total thickness of 1000 nm were prepared by direct current sputtering. Crystalline diameter in ZnO:Mg (200 nm)/ZnO (800 nm) improved to 26.5 nm compared with 21.9 nm in ZnO:Mg film. Mg-substitution of Zn-sites in ZnO:Mg shortened the c-axis with an increase in the optical bandgap of the bilayers to 3.35 eV (ZnO, 3.3 eV). Notably, the electrical conductivity of a ZnO:Mg (200 nm)/ZnO (800 nm) layer of 67.5 S cm−1 is superior to ZnO:Mg (1000 nm), 6.7 S cm−1. The charge carrier mobility for this bilayer is 21 cm2V − 1s − 1, at least 2.5 times higher than the best value reported for ZnO or metal-doped ZnO single layers. This increase in the carrier mobility is ascribed to the energy filtering phenomena due to the potential barrier at the ZnO:Mg/ZnO interface. This leads to a superior Seebeck coefficient of the bilayer (-175.2 μV K − 1 at 300 °C), nearly double that of a ZnO:Mg film. The energy filtering process significantly increased its power factor to 253.5 μW m − 1K − 2 at 300 °C, for the hetero-structured bilayer, nearly five times compared with that of ZnO:Mg. Further, it is comparable with power factor values of 100 – 200 μW m − 1K − 2 at 200 – 300 °C reported for other materials with energy filtering processes. Thus, simple cost-effective semiconductor structures with significant improvement in the thermoelectric parameters were achieved in ZnO:Mg/ZnO heterostructures thin film layers.