Strain-Modulated Bandgap and Piezo-Resistive Effect in Black Phosphorus Field-Effect Transistors

Abstract

Energy bandgap largely determines the optical and electronic properties of a semiconductor. Variable bandgap therefore makes versatile functionality possible in a single material. In layered material black phosphorus 1 5 , the bandgap can be modulated by the number of layers; as a result, few-layer black phosphorus has discrete bandgap values that are relevant for opto-electronic applications in the spectral range from red, in monolayer, to mid-infrared in the bulk limit 3,6 8 . Here, we further demonstrate continuous bandgap modulation by mechanical strain applied through flexible substrates. The strain-modulated bandgap significantly alters the charge transport in black phosphorus at room temperature; we for the first time observe a large piezo-resistive effect in black phosphorus field-effect transistors (FETs). The effect opens up opportunities for future development of electro-mechanical transducers based on black phosphorus, and we demonstrate strain gauges constructed from black phosphorus thin crystals.Under mechanical strain, the deformation of the atomic lattice is able to induce profound changes in the electronic structure of a crystalline material. This is best exemplified in doped silicon, where strain alters the energy bands of electron or hole carriers; the transfer of carriers to bands with small effective mass leads to drastic enhancement of carrier mobility (and thus conductivity) 9 13 . Strained silicon is, therefore, able to provide improved switching performance as the transistor dimension is aggressively scaled down in modern electronics 14,15 . Meanwhile, the large resistance response under strain has enabled the development of a myriad of silicon-based transducers 16 , such as strain and torque gauges, that are widely used in industrial applications. Page 3 of 17Black phosphorus, a two-dimensional (2D) material with a puckered honeycomb lattice, offers new possibilities. The puckered lattice in a monolayer, shown in Fig. 1a, can be viewed as rows of two orthogonally coupled hinges along the zigzag direction 17 . The structure makes black phosphorus a soft, and yet mechanically resilient, material that can withstand large strain modulation 18 . More importantly, deformation of the puckers under strain changes the configuration of pz orbitals near the band edges 19 ; modulating the black phosphorus bandgap (and therefore its material properties) via strain becomes a possibility. Indeed, it has been shown that a moderate high pressure of ~1.2 GPa can close the bandgap, and raise the conductance by one order of magnitude at room temperature 20 ; modulation of the optical properties was also observed in corrugated black phosphorus sheets 21 . Those studies hinted at strain as a powerful tool to modulate the electronic and optical properties of black phosphorus.Here, we observe a large piezo-resistive effect in black phosphorus FETs at room temperature. The piezo-resistive response (defined as the relative change in sample resistance, , at a given strain, ) varies with the gate doping, and reac...

The Optical Properties and Plasmonics of Anisotropic 2D Materials

“…The puckered structure of BP allows it to support a high level of strain, which can be used to modulate the band structure . Thus, one can utilize strain to modify the plasmons in BP thin films .…”

Piezoelectricity in Multilayer Black Phosphorus for Piezotronics and Nanogenerators

“…The angular dependence of the peak is used to determine the crystal orientation. Because the mode corresponds to the lattice vibration along the armchair direction, peak intensity is the strongest when the polarized incident laser is in this direction . Figure b shows peak intensity as function of polarization angle, where θ = 0° represents an incident laser angle parallel to the armchair direction.…”

Multistate Logic Inverter Based on Black Phosphorus/SnSeS Heterostructure

“…

Graphene, transition metal-dichalcogenides (TMDs), and black phosphorus (BP) are widely exploited as building blocks for such vdWs heterostructure due to their unique electrical and optical properties. [14][15][16][17] In the past years, a host of BP-based vdWs heterostructures such as graphene/ BP, TMDs/BP, and h-BN/BP architecture, have been fabricated to explore their electronic and photoelectric properties, which have shown promising applications for fieldeffect transistors (FETs), [18][19][20] photodetectors, [8,21,22] flexible devices, [23] memory device, [24] logic circuits, [25] and so on. [14][15][16][17] In the past years, a host of BP-based vdWs heterostructures such as graphene/ BP, TMDs/BP, and h-BN/BP architecture, have been fabricated to explore their electronic and photoelectric properties, which have shown promising applications for fieldeffect transistors (FETs), [18][19][20] photodetectors, [8,21,22] flexible devices, [23] memory device, [24] logic circuits, [25] and so on.

…”