[1Gp01-06] Thin Film (TF)

[1Gp02] High thermoelectric properties in epitaxial GeTe thin film by defect control

*Takafumi Ishibe^1,2, Nobuyasu Naruse³, Yutaka Mera³, Yuichiro Yamashita⁴, Yuji Ohishi⁵, Yoshiaki Nakamura^1,2 (1. Graduate School of Engineering Science, Osaka University, 2. OTRI, Osaka University, 3. Shiga Univ. Medical Science, 4. AIST, 5. Graduate School of Engineering, Osaka University)

Thermoelectric (TE) film on Si substrate is drawing much attention as a power source for internet of things sensor. The TE performance is quantified by a dimensionless figure-of-merit ZT; ZT=S²σTκ^-1, where S is Seebeck coefficient, σ is electrical conductivity, T is absolute temperature, and κ is thermal conductivity. The crucial bottleneck for high ZT is the interdependent relationship among three TE physical parameters. In recent years, GeTe is intensively studied because of low phonon group velocity and large band degeneracy, which lead to inherently-low κ and -high S²σ, respectively. However, the carrier concentration p is too high because of the generation of defect (Ge vacancy) working as carrier supplier. This high p degrades TE performance. In this study, we demonstrate the p decrease in epitaxial GeTe film by utilizing high volatility of Te atoms during the film growth in vacuum. This outstanding technique largely enhances TE properties.