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ZnO6GeF6 is Tetraauricupride structured and crystallizes in the trigonal R-3 space group. The structure is zero-dimensional and consists of three GeF6 clusters and three zinc;hexahydrate molecules. In each GeF6 cluster, Ge is bonded in an octahedral geometry to six equivalent F atoms. All Ge–F bond lengths are 1.83 Å. F is bonded in a single-bond geometry to one Ge atom.
In this work, two quaternary diamond-like semiconductors (DLSs) in the Cu-Zn-Ge-Se system, the known Cu 2 ZnGeSe 4 (also referred to as CZGSe) and the new Cu 4 ZnGe 2 Se 7 , are compared in terms of their crystal structures, electronic structures and physicochemical properties. Both compounds were prepared by high-temperature, solid-state synthesis at 800 degrees C. Single crystal X-ray diffraction was used to determine the structure of Cu 4 ZnGe 2 Se 7 . The structures of both Cu 2 ZnGeSe 4 and Cu 4 ZnGe 2 Se 7 can be considered as derivatives of cubic diamond. Cu 4 ZnGe 2 Se 7 , with a reduced symmetry due to the cation ordering pattern, adopts the Cu 4 NiSi 2 S 7 structure type, with space group C2. The corner-sharing tetrahedra in Cu 4 ZnGe 2 Se 7 are slightly distorted because the charge for some of the S 2 - anions is not compensated by the first-nearest-neighbor cations. Rietveld refinements using synchrotron X-ray powder diffraction data were used to assess the phase purity of the samples and confirm the bulk structural behavior. Diffuse reflectance UV/Vis/NIR spectroscopy shows that Cu 2 ZnGeSe 4 and Cu 4 ZnGe 2 Se 7 have direct optical bandgaps of 1.38 and 0.91 eV, respectively. Electronic structure calculations implementing density functional theory confirm the direct bandgap for Cu 4 ZnGe 2 Se 7 , with a calculated value of 0.62 eV. Both compounds are air stable, thermally stable up to relatively high temperatures, undergo phase transitions and have wide windows of optical clarity. The Kurtz-Perry powder technique was used to determine the second harmonic generation (SHG) responses using a commercial AgGaSe 2 standard. While Cu 4 ZnGe 2 Se 7 displays a weak SHG response, Cu 2 ZnGeSe 4 exhibits a response that is greater than several benchmark materials, with a large SHG coefficient, χ (2) , of 43 ± 6 pm/V at λ = 2900 nm.
Yb2(ZnGe)3 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Yb sites. In the first Yb site, Yb is bonded in a 10-coordinate geometry to six Zn and eight Ge atoms. There are a spread of Yb–Zn bond distances ranging from 3.08–3.26 Å. There are a spread of Yb–Ge bond distances ranging from 3.04–3.57 Å. In the second Yb site, Yb is bonded in a 6-coordinate geometry to five Zn and six Ge atoms. There are a spread of Yb–Zn bond distances ranging from 3.28–3.49 Å. There are a spread of Yb–Ge bond distances ranging from 3.02–3.14 Å. There are three inequivalent Zn sites. In the first Zn site, Zn is bonded in a 4-coordinate geometry to five Yb, one Zn, and four Ge atoms. The Zn–Zn bond length is 2.67 Å. There are a spread of Zn–Ge bond distances ranging from 2.51–2.69 Å. In the second Zn site, Zn is bonded in a 4-coordinate geometry to five Yb and four Ge atoms. There are a spread of Zn–Ge bond distances ranging from 2.49–2.78 Å. In the third Zn site, Zn is bonded in a 4-coordinate geometry to one Yb, one Zn, and four Ge atoms. There are a spread of Zn–Ge bond distances ranging from 2.53–2.74 Å. There are three inequivalent Ge sites. In the first Ge site, Ge is bonded in a 9-coordinate geometry to six Yb, two Zn, and one Ge atom. The Ge–Ge bond length is 2.48 Å. In the second Ge site, Ge is bonded in a 9-coordinate geometry to four Yb and six Zn atoms. In the third Ge site, Ge is bonded in a 7-coordinate geometry to four Yb and four Zn atoms.
The epitaxial growth of ZnGe(1-x)Si(x)P2-Ge alloys on GaP substrates by open tube organometallic chemical vapor deposition (OMCVD) is reported. The chemical composition of the alloys characterized by energy dispersive X-ray spectroscopy shows that alloys with x up to 0.13 can be deposited on (001) GaP. Epitaxial growth with mirror smooth surface morphology was achieved for x less than or equal to 0.05. Transmission electron microscopy (TEM) micrographs of these alloys show specular epitaxy and the absence of microstructural defects indicating a defect density of less than 10(exp 7) cm(sup -2). Selected area electron diffraction pattern of the alloy shows that the epitaxial layer crystallizes in the chalcopyrite structure with relatively weak superlattice reflections indicating certain degree of randomness in the cation sublattice. Hall measurements show that the alloys are p-type, like the unalloyed films; the carrier concentration, however, dropped about 10 times from 2 x 10(exp 18) to 2 x 10(exp 17) cm(sup -3). Absorption measurements indicate that the band tailing in the absorption spectra of the alloy was shifted about 0.04 eV towards shorter wavelength as compared to the unalloyed material. Diodes fabricated from the n(+)-GaP/p-ZnSiP2-ZnGeP2-Ge heterostructure at x = 0.05 have a reverse break-down voltage of -10.8 V and a reverse saturation current density of approximately 6 x 10(exp -8) A/sq cm.