Ba₂AgSi₃ Thin Films: Growth, Thermoelectric Properties, and Control of Their Conductivity Type via Impurity Doping Using First-Principles Calculations

Herein, Ba2AgSi3 thin films were fabricated by molecular beam epitaxy and their thermoelectric and electrical properties were investigated through experimental and computational approaches. The conductivity type of Ba2AgSi3 thin films varied with different Ba/Si supply ratios. Specifically, Si-poor thin films exhibited p-type conductivity, whereas Si-rich thin films exhibited n-type conductivity. Furthermore, a p-type thin film with a Ba-to-Si deposition rate ratio of 3.2 was epitaxially grown on a Si(111) substrate, which showed a high Seebeck coefficient of 296 μV K–1 and a high power factor of 250 μW m–1 K–2 at 311 K. First-principles calculations were performed to study the conductivity type and formation energy of Ba2AgSi3 when one atom in its structure was substituted by a group 13 (B, Al, Ga, or In) or 15 (P, As, or Sb) element. Calculation results indicated that substituting Si sites with B, Al, Ga, or In resulted in a Fermi level shift and p-type conductivity, and substituting Si sites with P, As, or Sb resulted in n-type conductivity. Conversely, the substitution of Ba or Ag sites with a group 13 or 15 element resulted in metallic properties and unstable modulation of the conductivity type. A comparison of the formation energies of impurity-doped Ba2AgSi3 revealed that B was the most suitable dopant for fabricating p-type Ba2AgSi3 among all group 13 elements, and all group 15 elements (P, As, and Sb) were suitable for fabricating n-type Ba2AgSi3. Our findings provide a basis for preparing customizable Ba2AgSi3-based thermoelectric materials.