High-performance n-type black phosphorus transistors with type control via thickness and contact-metal engineering.

David J Perello,Sang Hoon Chae,Young Hee Lee,Seunghyun Song

doi:10.1038/ncomms8809

David J Perello, Sang Hoon Chae + Show 2 more

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https://doi.org/10.1038/ncomms8809

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Abstract

Recent work has demonstrated excellent p-type field-effect switching in exfoliated black phosphorus, but type control has remained elusive. Here, we report unipolar n-type black phosphorus transistors with switching polarity control via contact-metal engineering and flake thickness, combined with oxygen and moisture-free fabrication. With aluminium contacts to black phosphorus, a unipolar to ambipolar transition occurs as flake thickness increases from 3 to 13 nm. The 13-nm aluminium-contacted flake displays graphene-like symmetric hole and electron mobilities up to 950 cm2 V−1 s−1 at 300 K, while a 3 nm flake displays unipolar n-type switching with on/off ratios greater than 105 (107) and electron mobility of 275 (630) cm2 V−1 s−1 at 300 K (80 K). For palladium contacts, p-type behaviour dominates in thick flakes, while 2.5–7 nm flakes have symmetric ambipolar transport. These results demonstrate a leap in n-type performance and exemplify the logical switching capabilities of black phosphorus.

Highlights

Recent work has demonstrated excellent p-type field-effect switching in exfoliated black phosphorus, but type control has remained elusive
We demonstrate that black phosphorus (BP) can serve as a high-performance n-type, ambipolar, or p-type transistor channel dependent on both flake thickness and contact metal
This is shown at 300 K in Fig. 1b, where unipolar behaviour and an extremely large but unsaturated (4-terminal) electron carrier mobility mFE 1⁄4 275 cm[2] V À 1 s À 1 at Vbg 1⁄4 70 V is observed

Summary

Introduction

Recent work has demonstrated excellent p-type field-effect switching in exfoliated black phosphorus, but type control has remained elusive. We report unipolar n-type black phosphorus transistors with switching polarity control via contact-metal engineering and flake thickness, combined with oxygen and moisture-free fabrication. P-type behaviour dominates in thick flakes, while 2.5–7 nm flakes have symmetric ambipolar transport These results demonstrate a leap in n-type performance and exemplify the logical switching capabilities of black phosphorus. BP samples, as no chemical vapor deposition (CVD) or epitaxial synthesis method exists Despite this limitation, initial reports for exfoliated flakes between 2 and 20 nm thick have demonstrated that the material can be used as a high-performance p-type conducting channel of 102–103 cm[2] V À 1 with room temperature hole s À 1(refs 8–14). We demonstrate that BP can serve as a high-performance n-type, ambipolar, or p-type transistor channel dependent on both flake thickness and contact metal. Al–BP Schottky-field-effect transistors (Schottky FETs) are contrasted with Pd–BP samples with lower contact resistance

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