Electronic structure, linear, nonlinear optical susceptibilities and birefringence of CuInX2(X = S, Se, Te) chalcopyrite-structure compounds

The electronic structure, linear and nonlinear optical properties have been calculated for CuInX 2 (X = S, Se, Te) chalcopyrite-structure single crystals using the state-of-the-art full potential linear augmented plane wave (FP-LAPW) method. We present results for band structure, density of states, and imaginary part of the frequency-dependent linear and nonlinear optical susceptibilities. We find that these crystals are semiconductors with direct band gaps. We have calculated the birefringence of these crystals. The birefringence is negative for CuInS 2 and CuInSe 2 while it is positive for CuInTe 2 in agreement with the experimental data. Calculations are reported for the frequency-dependent complex second-order non-linear optical susceptibilities χ 123 ( 2 ) ( ω ) MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacqaIXaqmcqaIYaGmcqaIZaWmaeaacqGGOaakcqaIYaGmcqGGPaqkaaGcdaqadaqaaiabeM8a3bGaayjkaiaawMcaaaaa@35B5@ . The intra-band and inter-band contributions to the second harmonic generation increase when we replace S by Se and decrease when we replace Se by Te. We find that smaller energy band gap compounds have larger values of χ 123 ( 2 ) ( 0 ) MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacqaIXaqmcqaIYaGmcqaIZaWmaeaacqGGOaakcqaIYaGmcqGGPaqkaaGcdaqadaqaaiabicdaWaGaayjkaiaawMcaaaaa@34D6@ in agreement with the experimental data and previous theoretical calculations. PACS Codes: 71.15.-m, 31.15.-p