| About this Abstract |
| Meeting |
2011 Electronic Materials Conference
|
| Symposium
|
2011 Electronic Materials Conference
|
| Presentation Title |
I3, Thermoelectric Properties of ErSb:InxGa1-xSb Thin Films Grown by MBE |
| Author(s) |
Hong Lu, Peter Burke, Nathan H. Hackman, John E. Bowers, Arthur C. Gossard |
| On-Site Speaker (Planned) |
Hong Lu |
| Abstract Scope |
Engineering of materials with nanostructures can result in improvement in the thermoelectric figure-of-merit, ZT. We have shown enhanced thermoelectric properties of III-V semiconductors by incorporating nanostructures of rare-earth compounds. In this work, ErSb:In<sub>x</sub>Ga<sub>1-x</sub>Sb is discussed as an example. Thin films of ErSb:In<sub>x</sub>Ga<sub>1-x</sub>Sb with different In composition have been grown on semi-insulating GaAs substrates using molecular beam epitaxy (MBE). By carefully dealing with the As-Sb interface, the highest In composition x has been pushed up to 0.73 with a lattice mismatch of 12.8% while good crystalline quality is maintained. The concentration of ErSb in these samples is kept at 0.8% by volume and the formation of ErSb nanoparticles within the In<sub>x</sub>Ga<sub>1-x</sub>Sb matrix has been observed by TEM. All the samples are codoped with beryllium for p-type behavior as is required for thermoelectric power generator modules. Thermoelectric properties, including electrical conductivity (σ), Seebeck coefficient (S) and thermal conductivity (κ) of the ErSb:In<sub>x</sub>Ga<sub>1-x</sub>Sb samples have been measured from room temperature up to 600K. The electrical conductivity was measured on van der Pauw geometry and the Seebeck coefficient was measured on a Seebeck bar sample for more accuracy. The thermal conductivity was measured using the 3ω method. Surface passivation by SiN<sub>x</sub>/SiO<sub>2</sub> was done to prevent the sample from melting and evaporating. Then lithography was used to define the contact areas followed by metal deposition for good ohmic contacts. Measurements were made under a vacuum of ~1x10<sup>-4</sup> torr. Among the ErSb:In<sub>x</sub>Ga<sub>1-x</sub>Sb samples with different In compositions, the one with high In composition x=0.69 yields the highest ZT≈0.57 at 530K. Higher thermoelectric power factor (S<sup>2</sup>σ) and ZT are achieved with higher In composition over the whole temperature range. Enhancement of thermoelectric properties by the ErSb nanoparticle incorporation is also shown by comparison of sample ErSb:In<sub>0.69</sub>Ga<sub>0.31</sub>Sb and sample In<sub>0.71</sub>Ga<sub>0.29</sub>Sb. At 530K, an improvement of 46% in ZT is achieved in this sample by 0.8% ErSb. The electrical contribution from the semi-insulating GaAs substrate starts to show up when the temperature reaches 500K, which prevents us from observing an increasing power factor and ZT. Therefore substrate removal and thin film transfer are important for reliable higher temperature measurements and currently in progress. |
| Proceedings Inclusion? |
Undecided |