First-principles Design And Optoelectronic Properties Of Two-dimensional α-AsP/γ-AsP Van Der Waals Homojunction

Materials composed of V-V group elements such as arsenic phosphide have attracted much attention due to their high carrier mobility and optoelectronic properties.The monolayer AsP has a direct bandgap of 1.55 e V calculated by the Heyd-Scuseria-Ernzerhof（HSE）hybrid functional,which has a direct bandgap that only absorbs energy through electronic transitions,similar to that of phosphorene.In particular,its carrier mobility has reached the order of 10⁴,which has excellent transistor application prospects.The As_xP_1-xalloy has been successfully prepared experimentally,which bandgap is tunable.This proves that it has excellent mechanical properties.There are many heterojunction solar cells designed with AsP as the donor material,in previous studies,but the theoretical research on homojunction solar cells is still lacking.By using first-principles calculations,we design aα-AsP/γ-AsP homojunction with minimum lattice distortion.The calculation found that the homojunction has excellent optoelectronic properties,which indicates its potential application in practice.In our study,the structural properties、optoelectronic properties and strain control of homojunctions are explored.The main conclusions obtained are:（1）By designing four different forms of stacking structure and get the most stable structure.It is found that theα-AsP/γ-AsP vertical homojunction has an indirect bandgap of 1.01 e V with an intrinsic type-II band alignment.（2）Although the light absorption coefficient ofα-AsP in the zigzag direction reaches up to 11×10⁵cm^-1,the optical absorption inα-AsP/γ-AsP homojunction has been improved to 16×10⁵cm^-1.Theα-AsP/γ-AsP homojunction exhibits obvious anisotropic characteristics and superior light absorption,which can become a promising candidate for photovoltaic applications.A high power conversion efficiency（PCE）of 21.08%is fonud inα-AsP/γ-AsP homojunction,which is comparable or even higher than previous reported solar cells.It is found that it has good carrier mobility of 10³cm²V^-1S^-1,which indicates that it can be used in transistors.（3）It was found that the indirect band gap of theα-AsP/γ-AsP homojunction can be changed to a direct band gap by applying an in-plane strain of 4%along the zigzag direction.Moreover,the intrinsic type-II band alignment can be tuned to type-I band alignment,which has potential application in optical devices.Under biaxially applied5%compressive strain,the intrinsic semiconducting properties are transformed into metallic ones.In summary,the construction of 2D van der Waals homojunctions is of great significance for obtaining 2D optoelectronic materials and devices with more desirable properties.