介觀下熱物理之單根高電阻三硒化二銻奈米線之量測方法與探討

Abstract

本論文研究為各別對單根三硒化二銻奈米線(Sb2Se3 nanowire)做三種物性量測。其分別為：( 1 ) 光與電的量測部份(Optic-Electric)、( 2 ) 熱與電的部份(Thermal-Electric)：求取席貝克系數(Seebeck coefficient)及最後 ( 3 )單根熱導率(Thermo-conductivity) 量測部份。 ( 1 ) 光與電的量測部份(Optic-Electric)：利用顯微之動態掃描光電流技術(Dynamic Scanning Photocurrent Microscopy – SPCM)；實驗上照光後，發現單根奈米線光電流的反應表現出暫態(transient)的電流峰值(current spike)特性，我們解釋其為單根三硒化二銻之熱釋電新現象(Pyroelectric effect)。透過Chynoweth方法，成功求出單根Sb2Se3奈米線熱釋電係數為60.09uC/m2K。由於Sb2Se3奈米線屬於非鐵電物質(Non-Ferroelectric)，但卻表現出高的熱釋電係數。推論因為照光缺陷(defect)的產生，造成材料空間電荷(space charge)，進而產生熱釋電效應。 ( 2 ) 透過半導體技術，我們製作量測單根奈米線席貝克之熱電量測元件 (TEP)。並對Sb2Se3奈米線量取三組配適(fitting)後之關係式做處理後，求得單根席貝克係數(Seebeck coefficient)，其值約為661.1uV/K；並為正型(positive)席貝克係數。在觀察席貝克係數與偏壓關係的實驗裡，由於奈米線擁有電性上高阻值的特性，我們相信在偏壓下的席貝克係數不適用Mott Formula，推測聲子拖曳效應(phonon drag effect)是影響其值主要的關鍵。 ( 3 ) 成功製做好懸空之量測熱導率的元件。並由懸空之感測薄膜與加熱薄膜上溫度上的變化對通入焦耳熱瓦數之關係，我們推出單根Sb2Se3奈米線熱導率，求得單根Sb2Se3奈米線熱導 k=0.0172W/mK

The works presented in this thesis focus on measurements on three kinds of physical properties from single antimony triselenide(Sb2Se3) nanowires. The content is divided into three parts：(1)optoelectrical measurements, (2)thermal-electric：Seebeck coefficient measurements, and (3)thermoconductivity measurements. Part one： A dynamic scanning photocurrent microscopy (SPCM) technique was applied to Sb2Se3 single nanowires. In this experiment, an electrical transient was observed for the first time when the single nanowires were illuminated laser pulses. It was considered as a new phenomenon from the pyroelectric effect uncovered in single Sb2Se3 nanowires. By using the Chynoweth method, we were able to successfully retrieve the pyroelectric coefficient 60.09uC/m2K of a single nanowire. Although the Sb2Se3 nanowire is classified as non-ferroelectric materials, but it exhibit a high pyroelectric coefficient. Therefore, we believe that the pyroelectric transient observed in the single nanowires is due to the defects produced under optical excitation which result to space charges generated in nanowires. Part two： Through the semiconductor manufacturing processes, a micro-device was fabricated to measure the Seebeck coefficient of single Sb2Se3 nanowires. A Seebeck coefficient of 661.1uV/k was obtained by data fitting and processing. The measured thermopower with a positive value indicates that the thermal transport is dominated by holes. In addition, we also observed increase in Seebeck coefficients when the bias voltage was increased. Due to the high resistivity of the Sb2Se3 nanowires, we believe that this phenomenon can only be interpreted by the phonon drag effect, but not by the Mott formula. Part three： In order to measure the thermal conductivity of single nanowires, micro-devices consisted of two adjacent suspended silicon nitride membranes were fabricated. A single Sb2Se3 nanowire was carefully placed on the device to bridge the two membranes. By accurately determining the relationship of temperature difference on each heating/sensing suspension membranes with the joule heating, we successfully deduced a thermal conductivity value of k=0.0172W/mK