Comparative study of doping properties and the effect on sliding barriers in γ-InSe

As the sliding ferroelectricity (SF) emerges as a potential approach to develop low-power ferroelectric electronics, fabricating high-quality SF van der Waals (vdW) crystals is of great importance. For the SF material γ-InSe, doping with proper elements has been verified to be an effective method to suppress the stacking faults and stabilize polarization. However, the underlying mechanism has not been understood, and the rule to select the proper doping elements remains unclear. Herein, using first-principles simulations, we perform a comparative study on the doping effects of several elements on γ-InSe, including Y, Dy, Bi, Sn, and Er. Interstitials in the vdW gap and substitutional antisites are found to be the most probable defects introduced by doping. Interestingly, the substitutional defects (, S n In , E r In , B i In , and B i Se ) are found to weaken the strength of interlayer coupling, leading to the decreased sliding barriers, while the interstitials defects ( Y i 1 and Dy i 1 ) are found to enhance the sliding barriers. Naturally, we propose that the interstitials in the vdW gap can suppress stacking faults, while the substitutional defects do not have this effect. The experimental comparation of typical InSe:Y and InSe:Bi, with the highest and lowest predicted sliding barriers, respectively, aligns well with our proposed mechanism. This work provides a new theoretical approach to determine the proper doping elements for high-quality SF materials.