高性能硒化銦電晶體在自組裝薄膜改質基板上的傳輸特性

Abstract

近年來，隨著過渡金屬硫族化物 （Transition metal dichalcogenides） 等具有半導體性質和層狀結構的二維材料成功以機械玻璃法製成，科學家對於二維半導體在奈米電子學等應用上有相當大的期許。過度金屬硫化物受限於其能帶結構和晶格缺陷，以及其對周圍介電質環境的敏感度，這類材料在載子傳輸的應用上相當有限。相較於過度金屬硫化物，硒化銦等金屬硫化物的電子具有較小的有效質量，因此在n-type半導體的應用上具有較大的可能性。在層狀二維半導體中，載子受限於二維方向的傳輸，使得上層與下層介面上的污染和不平整度對其傳輸特性有相當的影響。利用二維半導體對周圍介電質的敏感度，在其上下介面以具有層狀結構的氮化硼等二維絕緣體包覆，是至今能夠有效提升其傳輸表現的方法之一。截至今日，已經有一些期刊報導硒化銦在不同介電質上的傳輸性質。然而，不同結構中，硒化銦的載子遷移率對溫度的不一致性，顯示出其散射機制的不確定性。因此，這篇論文主要藉由不同溫度下的電性量測研究硒化銦場效電晶體的傳輸特性。我發現十八烷基三氯矽烷自組裝單分子薄膜基板對於提升硒化銦的傳輸表現有相當大的成效。十八烷基三氯矽烷自組裝單分子薄膜大幅提升了硒化銦電晶體的載子遷移率。在低溫下，其載子遷移率高達3000 cm2V-1s-1。不僅如此，硒化銦電晶體也因此顯現了金屬-絕緣相變的性質。藉由percolation 模型的分析，我認為硒化銦電晶體在低溫時主要受限於帶電的雜質散射。十八烷基三氯矽烷自組裝單分子薄膜透過其表面分子的疏水性，不僅大幅減少了帶電雜質，也有效地降低二維半導體與金屬接面上形成的Schottky barrier。此外，十八烷基三氯矽烷自組裝單分子薄膜裡的內建偶極場，有效地減少電子陷落（electron trapping）對硒化銦傳輸特性的影響，並對於其高表現的傳輸特性有著相當的貢獻。這些高表現的傳輸特性，證實了十八烷基三氯矽烷自組裝單分子薄膜能夠有效地提升二維半導體的傳輸特性，也說明了硒化銦對於往後奈米電子學的影響力。

Atomically thin two-dimensional (2D) layered semiconductors including transition metal dichalcogenides (TMDs), black phosphorous and indium selenide (InSe) hold great promises for electronics applications. The carrier transport in these transistors is influenced by charged impurities existing at the interface of the semiconductor and the dielectric surface. By encapsulating hexagonal boron nitride (h-BN), the high-quality 2D semiconductor-based transistors have been successfully achieved but with limited practicality. Various dielectric materials for InSe transistors have been studied; however, temperature-dependent mobility is inconsistent in the reports and the scattering mechanism is still indecisive. In this work, we analyzed the electronic transport properties of few-layer InSe transistors on octadecyltrichlorosilane (OTS) self-assembled-monolayer (SAM) functionalized dielectric surface by temperature-dependent transport measurements. The InSe flake is mechanically exfoliated on the OTS-functionalized SiO2 substrate. A h-BN flake is transferred on top of the InSe flake to effectively screen the charged impurities from the top surface of InSe, and to enable the chemical stability in ambient condition. In the presence of OTS surface, the InSe transistors exhibit enhanced field-effect mobility, metal-insulator transition (MIT), and reduction of Schottky barrier height. We observe the field-effect mobility as high as 3,000 cm2V-1s-1 at low temperature and the low percolation threshold density, both indicating the suppression of charged impurities by inserting the OTS SAM. Furthermore, the large activation energy of carrier traps leads to the reduced influence of carrier transport. Based on the high performance of the InSe transistors, the ultrasmooth OTS-functionalized substrate is promising for the next-generation nanoelectronic devices.