带隙
晶体结构
半导体
电子结构
价(化学)
直接和间接带隙
化学
二次谐波产生
结晶学
空间组
钻石
材料科学
激光器
光学
光电子学
X射线晶体学
计算化学
衍射
物理
有机化学
作者
Jordan C. Kelly,Chad E. Hoyer,Seung Han Shin,Jeong Bin Cho,Stanislav S. Stoyko,Allyson Bonnoni,Andrew J. Craig,Kate E. Rosello,Evan T O’Hara,Joon I. Jang,Jennifer A. Aitken
标识
DOI:10.1016/j.jallcom.2023.172437
摘要
The novel I4-II-IV2-VI7 quaternary diamond-like semiconductors (DLSs), Cu4ZnGe2S7 and Cu4CdGe2S7, were prepared from the constituent elemental powders at elevated temperatures. Cu4ZnGe2S7 crystallizes in the polar, chiral space group C2 and adopts the Cu4NiSi2S7 structure-type, which can be considered a derivative of the cubic diamond structure. The cadmium analog takes on the Cu5Si2S7 structure-type, which is related to the hexagonal diamond structure, and displays polar, Cc space group symmetry. Both compounds contain [Ge2S7]6- anions created by corner-sharing GeS4 tetrahedra. The crystal structures were carefully evaluated using: 1) extended connectivity tables, 2) minimum bounding ellipsoid analysis, and 3) bond valence sum (BVS) and global instability index (G) calculations. Both compounds are thermally stable up to temperatures exceeding 950 °C and melt incongruently. As assessed using diffuse reflectance spectroscopy, Cu4ZnGe2S7 and Cu4CdGe2S7 possess optical bandgaps of 1.65 eV and 1.90 eV, respectively, which are narrower than the analogous I2-II-IV-VI4 DLSs. Electronic structure calculations show that both compounds are direct-bandgap semiconductors with significant contributions of Cu-d and S-p orbitals to the states at the top of the valence band. While Cu4CdGe2S7 displays a weak second harmonic generation (SHG) response, the second-order nonlinear optical susceptibility, χ(2), of Cu4ZnGe2S7 is 14.8 ± 1.5 pm V-1, assessed using the Kurtz-Perry powder method and an optical-grade AgGaSe2 (AGSe) reference. Both compounds exhibit laser-induced damage threshold values similar to AGSe, ~0.1 GW cm-2, for λ = 1.064 μm using picosecond laser pulses. Most importantly, Cu4ZnGe2S7 exhibits a phase-matching behavior at λ = 3.1 μm. These results suggest that Cu4ZnGe2S7 holds potential for use in low-powered laser applications involving efficient wave mixing in the mid-IR region.
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