Solution-Based Property Tuning of Black Phosphorus

Abstract

The air instability of black phosphorus (BP) severely hinders the development of its electronic and optoelectronic applications. Although a lot of effort has been made to passivate it against degradation in ambient conditions, approaches to further manipulate the properties of passivated BP are still very limited. Herein, we report a simple and low-cost chemical method that can achieve BP passivation and property tailoring simultaneously. The method is conducted by immersing a BP sample in the solution containing both 2,2,6,6-tetramethylpiperidinyl-N-oxyl (TEMPO) and triphenylcarbenium tetrafluorobor in a mixture of water and acetone (v/v = 1:1). After the treatment, the BP sample is functionalized with TEMPO, which not only efficiently passivates BP but also p-dopes BP to a degenerated density level of 1013 cm–2. The performance of the BP field effect transistor is improved after functionalization with a high I on/I off ratio of 106 and carrier mobility of 881.5 cm2/(V·s). The functionalization-induced doping also significantly reduces the contact resistance between BP and the Cr/Au electrode to 0.97 kΩ·μm. Additionally, we observe a great reduction of BP electrical and optical anisotropies after functionalization. This chemical functionalization method provides a viable route to simultaneously passivate and tune the properties of BP.

Controllable Doping of Transition‐Metal Dichalcogenides by Organic Solvents

“…As illustrated in Figure 3d,e, the contact resistance after NMP doping decreased from 87 to 21.2 kΩ µm at V GS = 30 V, equivalent to four times. The values of contact resistance before and after doping were overall greater than those of previous literature,4,8,39 which may be attributed to wider electrode contact and no use of low work function metals such as titanium (Ti) to reduce Schottky barrier height and to facilitate electron injection 40,41. Contact resistances before and after doping as a function of V GS are displayed in Figure 3f.…”

“…Contact resistance before doping showed strong gate modulation behavior, which decreased as gate voltage increased and remained almost unchanged after doping. Sweeping from low to high gate voltage before doping, the reduced contact resistance was caused by the enhanced electron concentration in MoS 2 under metal contact due to enhanced electrostatic field 8. By contrast, the electron concentration of heavily doped MoS 2 did not change significantly with the electrostatic field.…”

“…Dopant molecules with different redox potentials or built‐in molecular polarities might generate surface charge transfer between dopant molecules and host materials 6. Examples include doping of molybdenum disulfide (MoS 2 ) by benzyl viologen, tungsten diselenide by octadecyltrichlorosilane, and black phosphorus by 2,2,6,6‐tetramethylpiperidinyl‐ N ‐oxyl 4,7,8. These literature results have shown that carrier concentration or mobility of devices can effectively be tuned by organic molecules, which have great potential in the assembly of function devices integrating 2D materials due to compatibility with the existing complementary metal oxide semiconductor technology 6.…”

“…Previously reported studies have used single molecule or binary mixtures to tune the electrical properties of single 2D material 4,7,8. In fact, in addition to molecular adsorption in these solutions, solvents may also interact with 2D materials during the doping process.…”

“…However, transfer characteristic curves after NMP doping cannot return back to the original characteristic profile (Figure S2, Supporting Information). Previous literature utilized the recovery of transfer characteristic curves to determine whether the doped state returned back to the original state 4,8. Thus, electrical measurement was introduced and evaluated the doping effect of residual molecules or solvents.…”