不論是理論或實驗皆已提出在熱電材料中置入低維度奈米結構確實可提供突破塊材熱電材料ZT < 1的瓶頸。矽、鍺材料是目前與積體電路製程相容性最佳的半導體材料之一，具有低成本與高熱穩定度的優勢。本論文即是利用上述特點，分別製作鍺量子點嵌於二氧化矽之薄膜以及矽鍺奈米柱 (線) 嵌於氮化矽之薄膜，以供微型熱電元件之應用。透過變溫熱傳導率以及電傳導率之量測分析來了解聲子與電子在量子點與奈米柱之傳輸行為，預期未來可直接整合於積體電路之微型熱電致冷器中，提供晶片上熱管理與散熱之功效。 在80 – 420 K的溫度範圍內，嵌於二氧化矽內平均直徑約4.92 – 7.36 nm鍺量子點薄膜之熱傳導率約為0.5 – 1 W/m?K。其熱傳導率與塊材鍺相比大幅下降了兩百倍之多，甚至比絕緣層二氧化矽之熱傳導率值下降了約五倍。重要的是，鍺量子點之熱傳導率會隨著量子點的大小而有系統性的變化，實驗得知其熱傳導率的下降幅度與嵌於二氧化矽中鍺量子點的直徑倒數有關。足見奈米結構之表面邊界散射非常有利於拖曳聲子之傳輸。此外，我們觀察到在100 – 400 K下，鍺莫耳百分比12 – 36 %的矽鍺奈米柱之熱傳導率普遍介於0.8 – 2 W/m?K之間，並且隨著鍺濃度的提升熱傳導率有逐漸下降之趨勢。其中電傳導率以p-type、鍺莫耳百分比24 %的矽鍺奈米線最高，經估算其ZT值在100 – 400 K範圍內最高達0.31。 Low-dimensional nanostructures embedded in thermoelectric materials has been demonstrated to be an effective approach to break through the bottle neck of ZT = 1. Silicon and germanium are presently the most compatible semiconductors with integrated circuit (IC) processing, which have the advantages of low cost and high stability. Based on the above-mentioned features, we fabricated thin-film-like Ge quantum dots and SiGe nanopillars (nanowires) for thermoelectric mircocooler applications. To understand the transport behaviors of phonon and electron in quantum dots and nanopillars, we conducted measurements of temperature-dependent thermal conductivities and electrical conductivities for these two systems. In the temperature of range 80 – 420 K, thermal conductivities for 4.92 – 7.36 nm Ge quantum dots in SiO2 matrix are around 0.5 – 1 W/m?K, which are much below the ones for bulk Ge and SiO2 with reduction factors of ~200 and ~5 respectively. Most importantly, there appears to be an inverse dot size dependence of thermal conductivities for Ge quantum dots in SiO2 system. It is obvious that surface/boundary scattering of nanostructures indeed cause phonon drag and make a large reduction in thermal conductivity. In addition, we have also observed that in the range 100 – 400 K, thermal conductivities for SiGe nanopillars with Ge mole fractions of 0.12 – 0.36 are between 0.8 – 2 W/m?K, and have an inverse dependence on Ge content. In our research, the condition of highest electrical conductivity is p-type SiGe nanowire with a mole fraction of 0.24. By calculation, its maximum ZT value is 0.31 in the temperature range of 100 – 400 K. It is expectable that these two systems would be applied to thermoelectric mircocooler for integrated circuits and provide the on-chip thermal management as well as heat dissipation in the near future.
