Ab initio study of the linear and nonlinear optical properties of chalcopyrite CdGeAs2

We present an ab initio theoretical study of the electronic, linear and nonlinear optical properties of CdGeAs2 using a pseudopotential plane-wave method. Specifically, we evaluate the band structure, density of states, charge density, the dielectric function ε (ω ) and the second harmonic generation response susceptibility View the MathML sourceχ312(2)(−2ω;ω,ω) over a large frequency range. As LDA underestimates the band gap, we have applied the GW approximation method to calculate the quasiparticle band structure and obtain an energy band gap in agreement with experiment. In this case the opening of the gap due to the GW correction can be used as scissor shift to calculate the linear and nonlinear optical properties. The intra- and inter-band contributions to the imaginary part of View the MathML sourceχ312(2)(−2ω;ω,ω) are presented over a broad energy range. It is found that the small energy gap semiconductor CdGeAs2 has larger values of ε 1(0) and View the MathML sourceχ312(2)(0) than other chalcopyrite structures.