Ab Initio Study Of Electronic Structure And Optical Properties Of A^ⅠB^ⅢC₂^Ⅵ

In the21st century, while under the condition of limited resources and environmentalprotection, human face to the realistic problems of realizing the sustainable development ofeconomy and society, especially the energy problem. Solar energy is a kind of radiant energy,which is not only cleanest but also the most reliable, and the sun will illuminate the earth foras long as5-6billion years, thus it is almost inexhaustible and has a unique attraction. Ourresearch object chalcopyrite semiconductors AIBIIICVI2, due to its large nonlinear opticalcoefficient, high transmittance in the far infrared and unique photovoltaic characteristics, iscurrently the most widely used photoelectric material and has been widely used in nonlineardevices，detectors，solar cells, etc. In addition to the pure ternary semiconductors, itsquaternary alloy systems become known to us recently as they have direct band gaps that canbe adjusted, which are in the range satisfactory for applications in solid state lighting，high-efficiency tandem solar cells and so on.This article uses the first principles calculation method based on density functionaltheory, also combining the theory of energy band structure and the generalized gradientapproximation, and Kohn-Sham equation to calculate the lattice structures、electrical andoptical properties of both CuAlX2(X=S, Se, Te) and CuGa(SexS1-x)2, then a comparative studyis made. The results show that: the band gaps of the three kinds of ternary semiconductorsdecrease along with the Ⅲ group elements from aluminum(Al) to gallium to indium while thecorresponding lattice constants、the static dielectric constants and refractive index increase. At the same time, the wave of both the dielectric constants and refractive index has a red shiftphenomenon. In addition, attributing to the similar electronic structures, the optical propertiesof the three kinds of pure compounds are rather similar, perform on the spectra curve ishaving broadly consistent behavior. What is worth mentioned is CuInTe2, which is differentfrom the other two compounds and has obvious anisotropy during0~2eV. The band gaps ofthe quaternary alloys decrease significantly along with the increase of component x and tendto1.4eV, which is the band gap of the ideal single section of solar cell, also there is noobvious improvement during the middle of the gradient process. Despite the large GGA errorin the calculations, which would not be assumed to be linear with composition x, differentbowing parameters are obtained. Furthermore, we also predict the anion position parameters uusing the model of Abrahams and Bernstein and compare them with the experimental andtheoretical data, which are only available for the ternary parents CuGaS2and CuGaSe2. Theamount of Se has almost no influence on the DOS of both Cu and Ga.