First-principles Study Of Physical Properties Of ZnXY₂（X=Si,Ge And Sn;Y=P,As And Sb）

The ZnXY2(X=Si,Ge and Sn;Y=P,As and Sb)compounds belong to the chalcopyrite structure semiconductors of the form Ⅱ-Ⅳ-Ⅴ2.They have been broadly applied in many fields including non-linear optics,semiconductor lasers,Infrared optical parametric oscillators and solar cells for their special electronic structure and optical properties.In order to further understand the correlation between the electronic structure and the nonlinear frequency doubling effect of them,it is necessary to carry out further theoretical research.The lattice constants,elastic constants,bulk modulus,shear modulus,Young’s modulus,Poisson’s ratio,electronic density of states,band structures and optical properties of the ZnXY2(X=Si,Ge and Sn;Y=P,As and Sb)compounds have been obtained using first-principles calculations based on the density function theory.The Debye temperature,bulk modulus,thermal expansion coefficients and heat capacity of these compounds were also calculated using quasi-harmonic Debye model.The results as shown in follows:(1)The calculated values of the lattice constant of ZnSiY2(X=Si,Ge and Sn)compounds are in accordance with the experimental values and other theoretical values.The calculated elastic constants satisfy the criteria of mechanical stability for the tetragonal systems and these compounds are mechanically stable.The elastic modulus shows that the resistance of compression are stronger than that of shear.The stiffness of ZnSiP2 is biggest among them.The B/G ratio shows that these compounds are brittle semiconductors.ZnSiP2,ZnSiAs2 and ZnSiSb2 are direct band gap semiconductors from their electronic structure.The difficulty of phase matching of ZnSiP2,ZnSiAs2 and ZnSiSb2 is reduced successively.However the difficulty of the light transmission in the IR region of them is increased in turn.Finally,the thermophysical properties show that the Debye temperature is reduced successively when Y atom varies from P to Sb for the ZnSi Y2 compounds.The bulk modulus of the compounds decreases with the increase of temperature,while increases with the increase of pressure.The thermal expansion coefficients and heat capacity of the compounds vary similarly with temperature and pressure,they increase with increasing temperature but decrease with increasing pressure.(2)The calculated values of the lattice constant of ZnGeY2(X=Si,Ge and Sn)compounds are in good agreement with the experimental values and other theoretical values.These compounds are mechanically stable.The elastic modulus shows that the compressive resistance of these crystal materials are stronger than their shear resistance.The stiffness of ZnGeP2 is biggest among them.The B/G ratio shows that these compounds are brittle semiconductors.ZnGeP2 is indirect band gap semiconductor,while ZnGeAs2 and ZnGeSb2 are direct band gap semiconductors.It is easier to realize the phase matching for ZnGeAs2.The difficulty of the light transmission in the IR region of them is increased in turn.The Debye temperature is reduced successively when Y atom varies from P to Sb for the ZnGeY2 compounds.The bulk modulus of the compounds decreases with the increase of temperature but increases with the increase of pressure.The thermal expansion coefficients and heat capacity of the compounds vary similarly with temperature and pressures,namely,they increase with increasing temperature but decrease with increasing pressure.(3)The calculated values of the lattice constant of ZnSnY2(X=Si,Ge and Sn)compounds accord with the experimental values and other theoretical values.These compounds are mechanically stable.The elastic modulus shows that the compressive resistance of these crystal materials are stronger than their shear resistance.The stiffness of ZnSnP2 is biggest among them.The B/G ratio shows that ZnSnP2 and ZnSnAs2 are brittle semiconductors,while ZnSnSb2 is a ductile semiconductor.ZnSnP2,ZnSnAs2 and ZnSnSb2 are all direct band gap semiconductors from their electronic structure.It is easier to realize the phase matching condition for ZnSnP2 and ZnSnSb2.The difficulty of the light transmission in the IR region of them is increased in turn.The Debye temperature is reduced successively when Y atom varies from P to Sb for the ZnSnY2 compounds.The bulk modulus of the compounds decreases with the increase of temperature but increases with the increase of pressure.The thermal expansion coefficients and heat capacity of the compounds vary similarly with temperature and pressures,namely,they increase with increasing temperature but decrease with increasing pressure.