Centre for Advanced 2D Materials, National University of Singapore , 117542, Singapore.
Department of Physics, National University of Singapore , 117551, Singapore.
Nano Lett. 2017 Sep 13;17(9):5361-5367. doi: 10.1021/acs.nanolett.7b01817. Epub 2017 Aug 16.
Because of the chemical inertness of two dimensional (2D) hexagonal-boron nitride (h-BN), few atomic-layer h-BN is often used to encapsulate air-sensitive 2D crystals such as black phosphorus (BP). However, the effects of h-BN on Schottky barrier height, doping, and contact resistance are not well-known. Here, we investigate these effects by fabricating h-BN encapsulated BP transistors with cobalt (Co) contacts. In sharp contrast to directly Co contacted p-type BP devices, we observe strong n-type conduction upon insertion of the h-BN at the Co/BP interface. First-principles calculations show that this difference arises from the much larger interface dipole at the Co/h-BN interface compared to the Co/BP interface, which reduces the work function of the Co/h-BN contact. The Co/h-BN contacts exhibit low contact resistances (∼4.5 kΩ) and are Schottky barrier-free. This allows us to probe high electron mobilities (4,200 cm/(V s)) and observe insulator-metal transitions even under two-terminal measurement geometry.
由于二维（2D）六方氮化硼（h-BN）的化学惰性，通常很少使用原子层 h-BN 来封装对空气敏感的 2D 晶体，如黑磷（BP）。然而，h-BN 对肖特基势垒高度、掺杂和接触电阻的影响尚不清楚。在这里，我们通过制造具有钴（Co）接触的 h-BN 封装 BP 晶体管来研究这些影响。与直接用 Co 接触的 p 型 BP 器件形成鲜明对比的是，我们观察到在 Co/BP 界面插入 h-BN 后会出现强烈的 n 型传导。第一性原理计算表明，这种差异源于 Co/h-BN 界面的界面偶极矩比 Co/BP 界面大得多，从而降低了 Co/h-BN 接触的功函数。Co/h-BN 接触具有低接触电阻（约 4.5 kΩ）和无肖特基势垒。这使得我们能够探测到高电子迁移率（4200 cm/（V s）），甚至在两端测量几何形状下也能观察到绝缘-金属转变。
