Evaluation of phase and thermoelectric properties of thin film SrSi₂

Abstract

We firstly prepared SrSi 2 thin films on insulating substrates and measured their thermoelectric properties. Thin films of SrSi system were deposited on (0001) Al 2 O 3 substrates by radio frequency magnetron sputtering method at various deposition temperatures and under various total deposition pressure. Constituent phases primary depend on the deposition temperature. The films deposited below 600°C consisted of amorphous or the metastable CaSi 2 structure phase. CaSi 2 structure phase was obtained at 600°C irrespective of the pressure and finally stable ¡-SrSi 2 (¡-phase) above 700°C. The films with CaSi 2 structure phase had low power factor below 10¯W m ¹1 K ¹2 for the temperature range between 100 and 400°C. On the other hand, the film with ¡-phase showed p-type conduction and good thermoelectric power factor beyond 700¯W m ¹1 K ¹2 at room temperature. This value is larger than the reported value of (111) one-axis-oriented Mg 2 Si films prepared by the same deposition process, maximum 130¯W m ¹1 K ¹2 at 300°C. The present result shows that ¡-phase is one of the promising candidates as thermoelectric materials.

Composition Dependence of Crystal Structures and Electrical Properties of Ca-Mg-Si Films Prepared by Sputtering

“…A comparison of the power factor of the obtained ptype Ca-Mg-Si film with those of the other p-type silicides reveals that the power factor of the present Ca-Mg-Si film is smaller than those reported for Sr-Si and Si-Ge films. [25][26][27] On the other hand, the present n-type films show better properties compared with the other silicides, but is smaller than widely investigated materials such as Bi-Te and Ag-Se. 28,29 However, it is possible to improve the present power factor by using doping to optimize the carrier concentration.…”

Enhanced Thermoelectric Properties of SrSi2 Composite Films with Cubic and Layered Polymorphs

“…15,16 It has been confirmed that SrSi 2 prepared by a sputtering method has two polymorphs. 13 The most stable semimetal cubic phase (hereafter described as the cubic phase) was obtained at above 700 °C, which is good for TE materials around room temperature. The other metastable phase with a layered structure (hereafter described as the layered phase), which formed below 600 °C, shows lower electrical resistivity and higher carrier density than the cubic phase, namely, benign metals.…”

“…10−12 Moreover, even when SrSi 2 was made into thin films, the power factor was ascertained to be less degraded in previous reports than was the case with other materials, in contrast to other materials. 13 Therefore, SrSi 2 seems to be advantageous for miniaturizing materials for use as heat sources for integrated devices, such as central processing units.…”

“…Silicide materials have advantages such as low environmental load, abundant constituent elements in the earth’s crust, and high compatibility with the Si process. Among these silicides, SrSi 2 with cubic symmetry − is a promising candidate TE material because it combines a high power factor near room temperature with eco-friendliness stemming from its nontoxic and naturally abundant constituent elements. − Moreover, even when SrSi 2 was made into thin films, the power factor was ascertained to be less degraded in previous reports than was the case with other materials, in contrast to other materials . Therefore, SrSi 2 seems to be advantageous for miniaturizing materials for use as heat sources for integrated devices, such as central processing units.…”

Thermoelectric Performance Enhancement of Film by Pulse Electric Field and Multi‐Nanocomposite Strategy

“…[5][6][7] However, most of these high-performance films still have the problems of relatively high cost, narrow applicable temperature, etc. While inexpensive thin films like oxides, [8][9][10] silicides, [11,12] borides, [13] Heusler alloys, [14,15] skutterudites, [16,17] etc., in general, have tended to show lower conversion efficiencies. Enhancement of conversion efficiency is limited mainly by two factors.…”