Study on PN heterojunctions associated bending coupling in flexoelectric semiconductor composites considering the effects of size-dependent and symmetry-breaking

Under bending deformation, size-dependent and structure-associated strain gradients can occur at the interface of a flexoelectric semiconductor (FS) PN heterojunction. Consequentially, a giant flexoelectric coupling will be induced to significantly enhance the flexoelectric effect of FS structures. To better understand the strain gradient–enhanced modulation performance and also reveal some other new phenomena, in this work, we theoretically and numerically study a beam shaped FS laminated composite subjected to pure bending loads. We first establish a one-dimensional theoretical model and then numerically explore the mechanical behaviors of the selected FS beam laminate. During analysis, structural symmetry breaking and size effect are considered by tuning the beam structural size and material parameters. We find that different from piezoelectric semiconductors whose mobile charges are driven by the piezo-potential, the mobile charges of FS composites induced by the flexo-potential are deterministically associated with strain gradients. Moreover, the strain gradients can exhibit a strong size-dependent effect and are quite sensitive to structural asymmetry and material parameters. We believe that our work can provide a new way to tune the carrier transport and electromechanical characteristics of a PN junction and thus can be useful to guide the next-generation flexotronic device designs.