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

摘要

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.