量子侷限效應與溫度對 Bi/p-Si蕭基接面能障的調變研究

Abstract

本研究旨在探討鉍（Bi）薄膜的量子侷限效應對Bi/p-Si蕭基接面電性行為之影響。透過Au/Bi/p-Si元件的變溫電容-電壓（C-V）與電流-電壓（I-V）量測，結合理論模擬分析，深入探討薄膜厚度與溫度變化對蕭基接面電性特性的影響機制。 在C-V量測部分，我們納入接面反轉層載子對電容響應的貢獻，並由1/C²-V圖擬合獲得蕭基能障(Schottky barrier height, SBH, ϕ_Bp)及矽基板之雜質濃度。結果顯示，當鉍薄膜厚度降至10 nm時，因量子侷限效應，費米能階上移並造成SBH提升。我們結合模擬發現當鉍塊材功函數設定為4.25 eV時，其模擬結果與實驗數據最為吻合，對應的Bi/p-Si接面SBH可達0.9 eV。值得注意的是，實驗所萃取之SBH分布明顯接近Schottky limit，顯示該接面具備近乎無Fermi Level Pinning （FLP）的特性，進一步驗證鉍為低態密度、低MIGS（Metal-Induced Gap States）材料。 I-V特性分析結果指出，元件在逆偏下展現電流隨偏壓顯著上升的行為；而順偏區則觀察到低溫條件下的電流斜率幾乎不隨溫度變化。為說明此行為，我們引入缺陷輔助穿隧模型，指出由於Bi/p-Si接面具有高SBH，熱離子發射（Thermionic Emission, TE）電流貢獻甚微，主導電流機制轉為包含缺陷輔助穿隧效應的復合電流。其中，逆偏區因強電場促使缺陷輔助穿隧路徑大幅增強，導致電流提升；而順偏區則受限於缺陷能級位置與空乏區內的載子濃度分布，進一步形成斜率隨偏壓變化的特徵性行為。 綜合而言，本研究揭示鉍功函數在量子侷限條件下可有效調變Bi/p-Si接面之能帶對齊與電性表現，展現Bi/p-Si理想蕭基接面的證據。

This study aims to investigate the impact of quantum confinement effects in bismuth (Bi) thin films on the electrical behavior of Bi/p-Si Schottky junctions. By performing temperature-dependent capacitance-voltage (C–V) and current-voltage (I–V) measurements on Au/Bi/p-Si devices, combined with theoretical simulations, we systematically explore the influence of Bi film thickness and temperature variation on the electrical characteristics of the junction. In the C–V analysis, the contribution from inversion-layer carriers at the junction was considered. Through 1/C²–V fitting, the Schottky barrier height (SBH, ϕ_Bp) and the impurity concentration of the silicon substrate were extracted. Results indicate that when the Bi thickness is reduced to 10 nm, strong quantum confinement raises the Fermi level and subsequently increases the SBH. Simulations show that a bulk Bi work function of 4.25 eV yields the best match with experimental data, corresponding to an SBH of approximately 0.9 eV at the Bi/p-Si interface. Notably, the experimentally extracted SBH values are close to the Schottky limit, suggesting a nearly Fermi-level-pinning-free (FLP-free) interface, thereby validating bismuth as a low-density-of-states and low-MIGS (metal-induced gap states) material. I–V characteristics reveal a significant current increase under reverse bias, while the forward-bias region shows that current slope remains nearly invariant with temperature at low temperatures. To explain this behavior, a trap-assisted tunneling (TAT) model was introduced. Due to the high SBH of the Bi/p-Si junction, thermionic emission (TE) is negligible, and the dominant transport mechanism transitions to recombination current with significant contributions from TAT. In reverse bias, strong electric fields enhance the tunneling pathway via defect states, leading to increased current. In forward bias, the current behavior is governed by the trap level position and the spatial distribution of carrier concentrations within the depletion region, resulting in bias-dependent slope characteristics. In summary, this work demonstrates that the work function of Bi can be effectively modulated under quantum confinement conditions, thereby tuning the band alignment and electrical performance of Bi/p-Si junctions. Our findings provide clear evidence of Bi/p-Si forming a near-ideal Schottky interface.