Department of Electrical Engineering , Stanford University , Stanford , California 94305 , United States.
Materials Science and Engineering , Stanford University , Stanford , California 94305 , United States.
Nano Lett. 2018 May 9;18(5):2822-2827. doi: 10.1021/acs.nanolett.7b05192. Epub 2018 Apr 12.
Black phosphorus (BP) is a promising two-dimensional (2D) material for nanoscale transistors, due to its expected higher mobility than other 2D semiconductors. While most studies have reported ambipolar BP with a stronger p-type transport, it is important to fabricate both unipolar p- and n-type transistors for low-power digital circuits. Here, we report unipolar n-type BP transistors with low work function Sc and Er contacts, demonstrating a record high n-type current of 200 μA/μm in 6.5 nm thick BP. Intriguingly, the electrical transport of the as-fabricated, capped devices changes from ambipolar to n-type unipolar behavior after a month at room temperature. Transmission electron microscopy analysis of the contact cross-section reveals an intermixing layer consisting of partly oxidized metal at the interface. This intermixing layer results in a low n-type Schottky barrier between Sc and BP, leading to the unipolar behavior of the BP transistor. This unipolar transport with a suppressed p-type current is favorable for digital logic circuits to ensure a lower off-power consumption.
黑磷 (BP) 是一种很有前途的二维 (2D) 材料，有望用于纳米级晶体管，因为其迁移率预计高于其他二维半导体。虽然大多数研究都报道了具有更强 p 型输运的双极性 BP，但对于低功耗数字电路来说，制造单极性 p 型和 n 型晶体管很重要。在这里，我们报告了使用功函数较低的 Sc 和 Er 接触的单极性 n 型 BP 晶体管，在 6.5nm 厚的 BP 中实现了创纪录的 200μA/μm 的 n 型电流。有趣的是，在室温下放置一个月后，所制造的、加帽的器件的电输运从双极性变为 n 型单极性。对接触截面的透射电子显微镜分析表明，界面处存在部分氧化金属的混合层。该混合层在 Sc 和 BP 之间形成了低 n 型肖特基势垒，导致 BP 晶体管的单极性行为。这种具有抑制 p 型电流的单极性传输有利于数字逻辑电路，以确保较低的关断功耗。
