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

Anh Tuan Thanh Pham, Phuong Thanh Ngoc Vo, Hanh Kieu Thi Ta, Hoa Thi Lai, Vinh Cao Tran, Tan Le Hoang Doan, Anh Tuan Duong, Ching Ting Lee, P. K. Nair, Yohandys A. Zulueta, Thang Bach Phan, Son D.N. Luu

Research output: Contribution to journalArticlepeer-review

Abstract

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 cm2 V − 1 s − 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 − 1 K − 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 − 1 K − 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.

Original languageEnglish
Article number138537
JournalThin Solid Films
Volume721
DOIs
Publication statusPublished - 2021 Mar 1

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Metals and Alloys
  • Materials Chemistry

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