First Principles Study On The Regulation Of Electronic Properties Of Bi-O-X(X=S,Se,Te) Materials

Semiconductor materials are the core of modern information technology and play a decisive role in the development of science and technology and social progress.Among them,Bi₂O₂X（X=S,Se,Te）materials have attracted much attention due to their excellent electronic and optoelectronic properties.In this work,electronic properties of Bi₂O₂X（X=S,Se,Te）under strain have been analyzed using first-principles calculations combined with the modified Becke-Johnson exchange potential.The key findings are as follows:（1）The results show that Bi₂O₂Se,Bi₂O₂S,and Bi₂O₂Te are indirect bandgap semiconductors with bandgaps of 0.63 e V,1.7 e V,and 0.2 e V,respectively.Bandgap size can be adjusted by in-plane tensile and compressive strain.A planar biaxial compressive strain of size-2%is applied to Bi₂O₂Se,and the top of the valence band shifts from the X point to the Gamma point into a direct band gap,which increases to0.7 e V.The indirect-direct band gap transition is also achieved when the uniaxial compression strain along the c direction is 1%,at which time the band gap size is 0.57e V.The effective masses of all three materials,Bi₂O₂Se,Bi₂O₂S and Bi₂O₂Te,are very low,which is one of the factors responsible for the high mobility.（2）The elastic constants,bulk modulus,shear modulus,Young’s modulus,Poisson’s ratio and the ratio of bulk modulus to shear modulus were calculated for three materials,Bi₂O₂Se,Bi₂O₂Te,and Bi₂O₂S.Bi₂O₂Se,Bi₂O₂Te,and Bi₂O₂S all meet the conditions required for the stability of the system,which proves that the system studied in this paper is stable.The Poisson’s ratios of Bi₂O₂Se,Bi₂O₂Te,and Bi₂O₂S were 0.359,0.314,and 0.372,respectively.From the Poisson’s ratio and the ratio of bulk modulus to shear modulus,it is clear that all three materials are ductile and have great potential for the fabrication of flexible electronic products.（3）In addition,the effective mass and mobility of carriers can be tuned by strain.Carrier mobility of Bi₂O₂Se increases significantly under uniaxial compressive strain.Extremely high carrier mobility and large anisotropy were found in Bi₂O₂Se,Bi₂O₂Te,and Bi₂O₂S.The calculated electron mobilitiesμin the a and c directions for Bi₂O₂Se at 2 K are 2.05×10⁶ cm²V^-1s^-1 and 1.8×10⁶ cm²V^-1s^-1,respectively.It can be seen that the electron mobility is much larger than the hole mobility in different directions,and the mobility in the a-direction is larger than that in the c-direction due to the unique energy band shapes and atomic orbitals of electrons and holes.The electron mobilities in the a-direction are 2513.6 cm²V^-1s^-1 and 2169.8 cm²V^-1s^-1 for the two materials Bi₂O₂Te and Bi₂O₂S,respectively,at room temperature.Finally,the carrier mobility change of Bi₂O₂Se at-2%to 2%strain was calculated,and the results showed that the electron mobility was more desirable at a compressive strain of 0.5%along the a-axis,and when the compressive strain was 2%along the c-axis,the electron mobility was more desirable and increased by 30%over the no-strain state.The extremely high mobility in Bi₂O₂Se,Bi₂O₂Te,and Bi₂O₂S makes them essential intermediate materials for fabricating ultra-high-speed and low-power electronic devices.Our work promises to open up a possible new avenue for designing direct bandgap nanostructures and tuning their bandgap width for application in high-performance optoelectronic devices.