矽(110)侷限效應在低溫環境下電子傳輸情形之研究

Abstract

本研究主要分析矽（110）侷限系統在低溫下電子傳輸情形。常溫下，載子之傳輸特性主要受聲子散射影響；有別於常溫，低溫下的載子傳輸須額外考慮進表面粗糙散射、遠程庫倫散射、雜質散射之影響。因此，文中首先根據量子效應計算出矽（110）侷限系統之子帶資訊，計算出材料聲子散射率，介電層所貢獻的遠程聲子散射率、表面粗糙散射率、遠程庫倫散射率、雜質散射率，讚以蒙地卡羅法評估出各條件下的電子遷移率。發現隨溫度調降，除表面粗糙散射數值不隨之改變外，其餘散射機制散射率皆隨溫度變小，原因為聲子佔居比例的下降，與固定通道載子濃度下屏蔽效應隨溫度下降的提升；因此，在此過程中，表面粗糙散射所佔的比例越來越高。除此之外，文中亦討論不同載子濃度下電子遷移率的變化。當通道載子濃度的低時，屏蔽效應減弱，遠程庫倫散射所佔比例提升；而隨載子濃度上升，屏蔽效應增強，遠程庫倫散射機制下降，以致電子遷移率升高；而再隨載子濃度越趨提升，電子分佈越靠近材料界面，因此電子受表面粗糙散射影響程度變得顯著，導致電子遷移率再次下降，最後得凹口向下的電子遷移率隨載子濃度分佈的趨勢。而此研究建立之低溫模型可推廣至其他系統，協助對該系統下載子遷移率的分析以及成因之釐清。

This study primarily analyzes the electron transport properties in silicon (110) confinement systems at low temperatures. At room temperature, the transport characteristics of carriers are mainly influenced by phonon scattering. However, unlike at room temperature, carrier transport at low temperatures must additionally consider the effects of surface roughness scattering, remote Coulombic scattering, and impurity scattering. Therefore, this paper first calculates the subband information of the silicon (110) confinement system based on quantum effects, and computes the phonon scattering rate of the material, the remote phonon scattering rate contributed by the dielectric layer, the surface roughness scattering rate, the remote Coulomb scattering rate, and the impurity scattering rate. Using the Monte Carlo method, the electron mobility under various conditions is evaluated. It is found that, as the temperature decreases, the scattering rates of all mechanisms except for surface roughness scattering decrease due to the reduction in phonon occupation and the enhancement of the screening effect at a fixed channel carrier concentration. Therefore, the proportion of surface roughness scattering increases during this process. Besides, this paper also discusses the changes in electron mobility under different carrier concentrations. When the channel carrier concentration becomes lower, the screening effect weakens, and the proportion of remote Coulombic scattering increases. As the carrier concentration increases, the screening effect strengthens, and the remote Coulombic scattering mechanism decreases, resulting in an increase in electron mobility. However, as the carrier concentration continues to rise, the electron distribution moves closer to the material interface, making the impact of surface roughness scattering more significant, leading to a decrease in electron mobility again. This results in a downward concave trend of electron mobility with respect to carrier concentration. The low-temperature model established in this study can be extended to other systems, helping the analysis and clarification of carrier mobility and its causes in those systems.