Papers by Keyword: Iron Disilicide

Abstract: Preparation of n-type β-FeSi₂/intrinsic Si/p-type Si heterojunctions was accomplished by facing-target direct-current sputtering (FTDCS) and measuring their current-voltage characteristic curves at low temperatures ranging from 300 K down to 50 K. A mechanism of carrier transport in the fabricated heterojunctions was investigated based on thermionic emission theory. According to this theory, the ideality factor was calculated from the slope of the linear part of the forward lnJ-V plot. The ideality factor was 1.12 at 300 K and increased to 1.99 at 225 K. The estimated ideality factor implied that a recombination process was the predominant mechanism of carrier transport. When the temperatures decreased below 225 K, the ideality factor was estimated to be higher than two and parameter A was estimated to be constant. The obtained results implied that the mechanism of carrier transport was governed by a trap-assisted multi-step tunneling process. At high forward bias voltage, the predominant mechanism of carrier transport was changed into a space charge limit current process.

Abstract: Recently, there is a strong interest in developing superior thermoelectric materials with the aim to improve the performance of a thermoelectric device. However, the performance of a thermoelectric generator (TEG) can be considerably improved also by applying a graded composition along the temperature gradient inside the thermoelectric device so that at each position the respective material achieves its maximum thermoelectric performance (TE FGM principle). Combining the high efficiency of Bi2Te3 (used at low temperatures) and general durability of FeSi2 (applied up to high temperatures) will result in a thermoelectric device with enhanced efficiency operating in air at a wide temperature range. The challenge is to contact these dissimilar materials without any negative impact on the performance of TEG. Besides providing a good electrical and thermal contact between Bi2Te3 and FeSi2 the junctions have to remain mechanically and chemically stable over long term. A Bi2Te3-SiO2 composite interlayer was used to adjust the different coefficient of thermal expansion (CTE) of FeSi2 (≈ 7·10-6 K-1) and Bi2Te3 (≈ 19·10-6 K-1). Due to low chemical stability of the Bi2Te3/FeSi2 contact at elevated temperatures (1000 h @ 300°C) a contacting material (diffusion barrier) based on Ni, Zn, Ti, and ZnTe was tested. Some contacts show excellent chemical and mechanical stability, though the electrical properties of the contacts do not meet the requirements (e.g. ZnTe is a wide gap semiconductor with high electrical resistivity). According to very recent studies at the Zn-based diffusion barriers a very thin layer of undoped ZnTe growing at the Bi2Te3/Zn interface causes the deterioration of the contact resistance. Ideas solving this problem are outlined and discussed.