Manipulating ambipolar phospherene to improve performance of electronic and optoelectronic devices

CHEN Wei ( Group Leader, Physics)

March 21, 2015

21 Mar 2015 NUS scientists report for the first time an effective modulation on ambipolar phospherene FETs, through in situ surface functionalization.A team led by Prof CHEN Wei from the Departments of Physics and Chemistry at NUS hasdemonstratedeffective surface transfer electron and hole doping onphospherene transistors through in situ surface functionalization with Cs₂CO₃ and MoO₃ overlayers, respectively. The electron mobility of phospherene transistors is found to be significantly enhanced to ~27 cm²V^-1s^-1 after Cs₂CO₃ modification, giving rise to a highly improved electron transport in the ambipolar characteristics of phospherene. In contrast, MoO₃ exhibits giant hole doping effects on phospherene devices accompanied by the nearly maintained hole mobility of ~200 cm²V^-1s^-1. The responsivity of phospherene photodetectors is largely enhanced to 2.56 AW^-1 and 1.88 AW^-1 after MoO₃ and Cs₂CO₃ doping respectively.

Phospherene, a fast emerging 2D material, is considered a promising candidate for future functional devices owing to its outstanding electronic and optoelectronic properties. The intrinsic band gap allows phosphorene to be easily modulated between ON and OFF conduction states. Phosphorene configured FETs demonstrate clear ambipolar transport behavior with remarkably high hole mobility up to ~1000 cm²V^-1s^-1 and on/off ratio ~10⁵ at room temperature, making this material suitable for transistors. However, the ambipolar characteristics of phospherene show the strong asymmetry between electron and hole transport, making it difficult to fulfill the complementary logic devices on a single phospherene flake (see Figure).

The results promise a simple method to either electron or hole dope phospherene and thus effectively tailor the ambipolar characteristics of phospherene transistors to realize highperformance phospherene based complementary logic circuits as well as other functional electronic and optoelectronic devices.

chen wei large

The images shows (on the left) a schematic illustration of phosphorene device coated by Cs₂CO₃. (On the right) Linear plot of the transfer curves at 0.5 nm and 10 nm Cs₂CO₃ coverage with respect to the pristine BP.The electron transport of BP FET was significantly improved after Cs₂CO₃ modification, leading to either a more balanced ambipolar or even electron-transport dominated FET characteristic. (Image credit: Chen Wei)

Reference

Xiang D, Han C, Wu J, Zhong S, Liu YY, Lin JD, Zhang XA, Hu WP, Özyilmaz B, Castro NetoAH, Wee ATS, Chen W. “Surface Transfer Doping Induced Effective Modulation on Ambipolar Characteristics of Few-layer Black Phosphorus” Nature Communications 6 (2015) 6485 DOI: 10.1038/ncomms7485