The Relationship between Nanocluster Precipitation and Thermal Conductivity in Si/Ge Amorphous Multilayer Films: Effects of Cu Addition

Abstract

We have used a molecular dynamics technique to simulate the relationship between nanocluster precipitation and thermal conductivity in Si/Ge amorphous multilayer films, with and without Cu addition. In the study, the Green-Kubo equation was used to calculate thermal conductivity in these materials. Five specimens were prepared: Si/Ge layers, Si/(Ge + Cu) layers, (Si + Cu)/(Ge + Cu) layers, Si/Cu/Ge/Cu layers, and Si/Cu/Ge layers. The number of precipitated nanoclusters in these specimens, which is defined as the number of four-coordinate atoms, was counted along the lateral direction of the specimens. The observed results of precipitate formation were considered in relation to the thermal conductivity results. Enhancement of precipitation of nanoclusters by Cu addition, that is, densification of four-coordinate atoms, can prevent the increment of thermal conductivity. Cu dopant increases the thermal conductivity of these materials. Combining these two points, we concluded that Si/Cu/Ge is the best structure to improve the conversion efficiency of the Si/Ge amorphous multilayer films.

Amorphous Framework in Electrodeposited CuBiTe Thermoelectric Thin Films with High Room-Temperature Performance

“… 21 The nanophases that formed in the thin films are believed to be the effect of the metal-induced crystallization of the dopant metals. 30 Although control over the nanophases and their transport properties is still challenging, it can be achieved through a desirable choice of dopant and an efficient method for thin film deposition. Among the various methods reported earlier, including atomic layer deposition, 31 molecular beam epitaxy, 32 , 33 arc-melting, 34 etc., electrodeposition is one of the most versatile fabrication methods owing to its simple operation at low temperature, low cost, and high deposition rate with flexibility to design a material with tunable properties.…”

“… 37 , 38 Until now, the effect of Cu doping in Bi 2 Te 3 /Bi 2 Se 3 has been reported by different groups through Cu intercalation, Cu electrodeposition, etc., which has shown enhancement in the thermoelectric properties. 30 , 38 − 40 Recently, Chen et al have found that the formation of Cu clusters is due to migration from quintuple layers with aging. 41 Burton et al showed extremely high thermoelectric performance ( S = −390 μV K –1 ) in electrochemically copper-doped bismuth tellurium selenide thin films.…”

“…This was mainly due to the carrier filtering effect by introducing a conducting nanophase at the interface to act as phase boundaries . The nanophases that formed in the thin films are believed to be the effect of the metal-induced crystallization of the dopant metals . Although control over the nanophases and their transport properties is still challenging, it can be achieved through a desirable choice of dopant and an efficient method for thin film deposition.…”

“…The extra atoms play a key role and should be codeposited stably with Bi and Te to control their composition and crystallinity; therefore, it is important to select the appropriate element. Because of its small electrode potential difference (30–50 mV) from Bi, the Cu atom can be codeposited over a wide range of potential/current density without depolarization effect [Abner Brenner, Thesis]. , Until now, the effect of Cu doping in Bi 2 Te 3 /Bi 2 Se 3 has been reported by different groups through Cu intercalation, Cu electrodeposition, etc., which has shown enhancement in the thermoelectric properties. ,− Recently, Chen et al have found that the formation of Cu clusters is due to migration from quintuple layers with aging . Burton et al showed extremely high thermoelectric performance ( S = −390 μV K –1 ) in electrochemically copper-doped bismuth tellurium selenide thin films .…”