Second-Harmonic Generation and Crystal Structure of the Diamond-like Semiconductors Li₂CdGeS₄ and Li₂CdSnS₄

Abstract

The semiconductors Li(2)CdGeS(4) and Li(2)CdSnS(4), which are of interest for their nonlinear optical properties, were synthesized using high-temperature solid-state and polychalcogenide flux syntheses. Both compounds were found to crystallize in Pmn2(1), with R1 (for all data) = 1.93% and 1.86% for Li(2)CdGeS(4) and Li(2)CdSnS(4), respectively. The structures of both compounds are diamond-like with the tetrahedra pointing in the same direction along the c axis. The alignment of the tetrahedra results in the structure lacking an inversion center, a prerequisite for second-harmonic generation (SHG). A modified Kurtz nonlinear optical powder technique was used to determine the SHG responses of both compounds. Li(2)CdGeS(4) displayed a type I phase-matchable response of approximately 70x alpha-quartz, while Li(2)CdSnS(4) displayed a type I non-phase-matchable response of approximately 100x alpha-quartz. Diffuse-reflectance spectroscopy was used to determine band gaps of 3.10 and 3.26 eV for Li(2)CdGeS(4) and Li(2)CdSnS(4), respectively.

First Principles Investigations on Structural, Elastic, Electronic, and Optical Properties of Li₂CdGeS₄

“…12). The calculated band gap of LDA result agrees with the previous theoretical value (2.83 eV), 12) but is smaller than the experimental value 3.10 eV, 11) due to the well-known underestimation of conduction band state energies in DFT calculations. In Table 3, we collected the direct and indirect band gaps and compared them with experimental 11) and theoretical 12) ones.…”

“…The calculated band gap of LDA result agrees with the previous theoretical value (2.83 eV), 12) but is smaller than the experimental value 3.10 eV, 11) due to the well-known underestimation of conduction band state energies in DFT calculations. In Table 3, we collected the direct and indirect band gaps and compared them with experimental 11) and theoretical 12) ones. From Table 3, we can find that the band gap in LDA is larger than that in GGA, it is perhaps due to the smaller lattice constants predicted in LDA and the difference of methods in LDA and GGA which deal with the electron density.…”

“…Meanwhile, the axial ratio c/a with minimum total energy is also obtained. By fitting the calculated energyvolume (EV) data to the three-order natural strain equation of state, 18) the calculated lattice constants a, b, c, V 0 , bulk modulus B 0 at zero pressure and its pressure derivative B 0 A with available experimental 11) and theoretical 12) data for Li 2 CdGeS 4 are summarized in Table 1, which shows that the calculated values of GGA calculation are in better agreement with the experiments than that of LDA calculations. Unfortunately, there are no experimental value of bulk modulus and its pressure derivative for comparisons.…”

“…However, there are only a few studies about Li 2 CdGeS 4 . Lekse et al 11) reported that semiconductor Li 2 CdGeS 4 was firstly synthesized in both single crystal and polycrystalline forms by high-temperature solid-state and polychalcogenide flux syntheses. They also proposed that the replacement of Cu by Li may enlarge the band gap of this compound, which may result in higher laser damage thresholds.…”

First-principles study on electronic and optical properties of Cu2ZnSiV I4 (VI=S, Se, and Te) quaternary semiconductors

“…These materials are considered to have potential applications in photovoltaic, thermoelectric and optoelectronic devices. [1][2][3][4][5][6][7] For example, Cu 2 ZnSnS 4 and Cu 2 ZnSnSe 4 are found to be good substitutes of conventional CIG(S, Se) solar cells because their band gaps are very close to 1.5 eV.…”