利用光電子激發能譜儀及電性分析鐵矽化合物及砷化鎵間之蕭特基能障

Abstract

金半接面無疑在電子元件及自旋電子元件中扮演極其重要的腳色，當中蕭特基能障是金半接面中最重要的特性，從發現到現在已經超過七十年，不同的模型試圖去解釋其整流的行為及分析，但至今卻沒有一個模型能詳細的解釋其行為，根據ITRS預測，在西元2021年，電晶體閘極之長度將會縮短至10 nm，在以三五族材料為通道的高效能補償式電晶體下，獲得更低的金半接面之接觸電阻及調控它勢必成為我們應當重視的議題。 然而蕭特基能障與金半介面之原子結構間息息相關，蕭特基能障的形成是一個相當複雜的問題，為了研究蕭特基能障，我們設計了一系列的實驗。在本論文之實驗中，鐵矽化合物(Fe3Si)及砷化鎵(GaAs)在超高真空分子束磊晶儀(UHV-MBE)系統及分析系統下操作，包含成長III-V族化合物砷化鎵為主的分子束磊晶儀、在無砷環境下成長金屬之分子束磊晶儀、X光和紫外光之光電子激發分析能譜儀(XPS and UPS)。 利用四點探針量測儀，我們得到蕭特基二極體隨溫度變化之電壓電流趨勢圖，經由計算可發現電流之自然對數和電壓作圖有明顯線性關係。 比較電性量測，我們做了更進一步地分析，在成長上金屬前，利用紫外光之光電子激發分析能譜可得知砷化鎵之游離能和費米能階至價帶最大值能距，長上金屬的過程可以藉由X光之光電子激發能譜儀得知原子之內層電子鍵結能量，隨著沉積不同的金屬厚度我們可以明顯看到能帶彎曲，最後再用紫外光之光電子激發分析能譜得到鐵矽化合物之功函數，如此可以完整地呈現金半接面之能帶圖，且不需多餘的假設即可直接量測得到蕭特基能障，而我們也藉由UPS量測證實真空能接不連續於介面，確實有介電層存在於鐵矽化合物和砷化鎵之金半接面中。

Metal-semiconductor (MS) interfaces are an essential part in electronic and spintronic devices; therefore, Schottky barrier heights (SBH) are clearly the most important property of an MS interface. For over 70 years, various models have been proposed to explain how these rectifying barriers are determined. But thus far no theory emerges which gives explicit account of the experimental results. According to the prediction of International Technology Roadmap for Semiconductors (ITRS), the physical gate length of device will be scaling down to 10 nm in 2021. In ultimate CMOS technology with III-V semiconductors as the channel material, extremely low Ohmic contacts are demanded, in which the understanding and manipulation of the SBH is a must to achieve the low resistivity. However, the formation of the Schottky barrier height (SBH) is an extremely complex problem because of the dependence of the SBH on the atomic structure of the metal-semiconductor (MS) interface. In order to study the mysterious SBH, we designed the series experiments. In this work, the growth of Fe¬3Si on GaAs was carried out in a multi-chamber growth/analysis system, including a GaAs-based III–V molecular beam epitaxy (MBE) chamber, a As-free metal MBE chamber and an X-ray vacuum (UHV) modules. The temperature dependence of the current-voltage characteristics of Fe3Si/GaAs(100) was measured by contact probe techniques. Our results indicate that the logarithmic plot of current as a function of bias voltage across the Schottky diode gives a linear relationship. Comparison of results of I-V measurement, we precisely obtained the Schottky barrier heights from XPS and UPS measurements. Furthermore, the ionization energy of GaAs(100) 4x6 clean surface and work function of Fe3Si were measured by UV source HeI lamp in the same XPS chamber. Also, due to the larger escape length of XPS photoelectrons, it is possible to measure the band bending in the substrate at relatively high overlayer depths independently from the overlayer band bending. The band diagrams of Fe3Si/GaAs were absolutely shown clear in this experiments. Furthermore, vacuum energy misalignment at Fe3Si and GaAs interface was demonstrated and the SBH have been directly determined via this method without any assumptions.