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  • 學位論文

聚焦離子束沈積鉑與p型矽奈米線接觸之特性研究

Characterization of Disordered p-Si Nanowire Contacted by Focused-Ion-Beam-Deposited Pt

指導教授 : 何志浩
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摘要


我們利用化學濕蝕刻法在p型硼摻雜矽基板上製作出單晶的矽奈米線,並且利用聚焦離子束技術沈積鉑,將單根矽奈米線和基板上外圍的金電極連接,最後進行電性的兩點和四點量測。四點量測實驗可去除接觸電阻的影響,得到更精準的奈米線電性。 在第一部份中,我們利用變溫的四點量測來研究經過聚焦離子束鉑沈積後的p型矽奈米線傳導機制。由穿遂式電子顯微鏡分析證實鉑電極下的矽形成非晶結構。莫特變程跳躍理論被認為是此非晶結構矽奈米線在室溫下的主要傳輸機制,經由莫特變程跳躍理論的公式計算可得莫特參數,例如在費米能階的侷限態密度、最佳跳躍距離以及平均跳躍能量,並且與理論值一致。 在第二部份中,由於聚焦離子束鎵離子引起的矽奈米線非晶化,我們發現鉑和矽奈米線會形成相當低特性接觸電阻的歐姆接觸,其值約為1.54×10-6 (Ω cm2)。此歐姆接觸是由於鎵離子在矽奈米線結構上引起的非晶化所造成。擴散理論被認為主導鉑和矽奈米線接觸面的傳輸特性。由非晶化所引起的介面態及外加偏壓引起的映像電荷效應造成非常低的蕭基能障高度,可用來解釋介面上非常低的特性接觸電阻。載子濃度2.79×1017 (cm-3)也可被估計出來。相較於其它的矽奈米線金屬接觸,如此低的特性接觸電阻可實際應用於整合矽奈米線與相關的元件、電路。

並列摘要


Galvanic wet etching was applied to fabricate single-crystalline Si NWs using p-type Si (100) substrates with boron doping. Focused ion beam-deposited Pt was utilized to connect Au/Cr electrodes with the individual Si NW. The DC electrical measurement was performed by two-probe and four-probe testing. The four-probe measurement provides more accurate electrical properties of Si NWs without considering contact resistance. First, we investigate the conduction mechanism of individual p-Si NWs after FIB-Pt deposition by temperature-dependent four-probe measurements. Transmission electron microscopy (TEM) analysis confirms the existence of FIB-induced amorphized Si underneath Pt contacts. Mott variable range hopping (Mott-VRH) is responsible for the conduction of such disordered p-Si NWs below room temperature. Mott parameters, such as the density of localized states at Fermi level, optimum hopping distance, and average hopping energy, are obtained by fitting the formula of Mott-VRH and are consistent with the theoretical values. Secondly, an Ohmic contact was formed with a relatively low specific contact resistance of 1.54×10-6 Ω cm2 due to Ga-ion-induced amorphization of Si NWs underneath the Pt contact. The diffusion theory is considered to be the major transport mechanism of FIB-Pt contacts to disordered Si NWs. A sufficiently low Schottky barrier height associated with interface states raised from Pt-amorphized Si junction and with an image force induced by the applied bias can be implemented to elucidate ultralow ρc. The carrier concentration of 2.79×1017 cm-3 is also estimated. The value of ρc lower than that of any known contact to Si NWs paves the way for integrating NWs with electronic devices and circuits.

參考文獻


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