Bulk photovoltaic effect at infrared wavelength in strained Bi₂Te₃ films

As a prominent three-dimensional (3-D) topological insulator, traditional thermoelectric material Bi₂Te₃ has re-attracted greater interest in recent years. Herein, we demonstrate for the first time that c-axis oriented strained Bi₂Te₃ films exhibit the bulk photovoltaic effect (BPVE) at infrared wavelengths, which was only found in wide band-gap ferroelectric materials before. Moreover, further experiments show that the bulk photovoltaic effect probably comes from the flexoelectric effect which was induced by the stress gradient in strained Bi₂Te₃ films. And we anticipate that the results are generalizable to other layer-structured or two-dimensional (2-D) materials, e.g., Bi₂Se₃ and MoS₂.