In-Plane Strain-Modulated Photoresponsivity of the α-In₂Se₃-Based Flexible Transistor

Abstract

Two-dimensional (2D) van der Waals (vdW) materials have been proven to be functional materials with excellent performance among flexible functional optoelectronics. Static strain may have a great influence on photoinduced charge carriers in a 2D vdW piezoelectric semiconductor. However, only a few works pay attention to the static-strain-modulated photoresponsivity of 2D vdW ferroelectric materials. α-In2Se3, a 2D vdW ferroelectric semiconductor from the family of III–VI compounds in the form of III2–VI3, has attracted considerable attention for the study of high-performance nanodevices. In this study, we investigate a flexible α-In2Se3-based transistor on a polyethylene terephthalate substrate. A competitive mechanism of carrier mobility and piezoelectric/ferroelectric polarization exists in the transistor when in-plane strain is applied. The carrier mobility modulates separation and transport of electron–hole pairs, whereas piezoelectric/ferroelectric polarization charges modulate the local band profile tilting. The optimized photoresponsivity is increased by 200% (illumination intensity is about 454 μW/cm2) while introducing a −0.15% compressive strain when the wavelength of the laser is about 405 nm. Our results reveal the strain-modulated photoresponsivity in an α-In2Se3-based flexible transistor, which may offer an approach to understand strain-modulated flexible functional optoelectronics.

Piezotronics in two‐dimensional materials

“…According to the mechanism of piezotronics from 2D materials, the output current will be regulated to increase or decrease when applied the external strain. Thus, the gauge factor for related sensors will be enhanced or reduced, causing scrambling research of diverse applications, such as various sensors, 158–180 nanogenerators, 181–192 piezo‐catalysis, 193–195 information storage, 196–199 and so on.…”

“…Piezo‐potential promotes separation and transport of photogenerated electrons and holes and increases the output current, causing the enhanced photo‐response and developed piezophototronics of 2D materials 171–177 . Those piezophototronic sensors can be divided into two types of contact: metal and 2D materials, and p‐n junctions.…”

“…Those piezophototronic sensors can be divided into two types of contact: metal and 2D materials, and p‐n junctions. For the contact of metal and 2D materials, MoS 2 , 22,171,178 WSe 2 , 172 α‐In 2 Se 3 , 173 γ‐InSe, 174 and In 1− x Sn x Se, 175 were investigated widely. It is interesting that by repairing the defect in MoS 2 flexible phototransistor, a prominent piezophototronic sensor was realized, where 5.6‐fold enhancement of responsivity is achieved under a 0.42% tensile strain (Figure 8A–C).…”

Strain-Modulated Photoelectric Responses from a Flexible α-In2Se3/3R MoS2 Heterojunction

“… and , where and are the doping concentrations in the 3R MoS 2 and α-In 2 Se 3 flakes, respectively; is the built-in voltage; q is the elementary charge, and are the permittivity of 3R MoS 2 and α-In 2 Se 3 flakes, respectively [ 46 – 49 ]. As the carrier concentration, layer thickness and permittivity for the MoS 2 (In 2 Se 3 ) flake are cm −3 , nm, ( ) [ 50 – 53 ]. where is the permittivity in vacuum, the doping concentration could be estimated as cm −3 .…”

“…Since the theoretical d 13 magnitude of α-In 2 Se 3 is 3.08 pm V −1 , a factor of 15 larger than that of 3R MoS 2 , we could ignore the out-of plane piezoelectric polarization in the 3R MoS 2 flake for simplicity of discussion [ 30 , 54 ]. Under a tensile (compressive) strain in dark, positive (negative) piezoelectric charges could emerge at the bottom surface of the α-In 2 Se 3 flake [ 50 ]. The positive (negative) piezoelectric charges lower (raise) the energy band near the interface of the α-In 2 Se 3 flake, as shown in Fig.…”