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GeH4 is alpha carbon monoxide-like structured and crystallizes in the orthorhombic Cmcm space group. The structure is zero-dimensional and consists of four germanium molecules and eight hydrogen molecules.
GeH4 crystallizes in the orthorhombic Cmmm space group. The structure is two-dimensional and consists of two hydrogen molecules and one GeH2 sheet oriented in the (0, 0, 1) direction. In the GeH2 sheet, Ge2+ is bonded in a square co-planar geometry to four equivalent H+0.50- atoms. All Ge–H bond lengths are 1.79 Å. H+0.50- is bonded in a linear geometry to two equivalent Ge2+ atoms.
GeH4 is Silicon tetrafluoride-like structured and crystallizes in the monoclinic P2/c space group. The structure is zero-dimensional and consists of four germane molecules. Ge2+ is bonded in a tetrahedral geometry to four H+0.50- atoms. There is two shorter (1.53 Å) and two longer (1.54 Å) Ge–H bond length. There are four inequivalent H+0.50- sites. In the first H+0.50- site, H+0.50- is bonded in a single-bond geometry to one Ge2+ atom. In the second H+0.50- site, H+0.50- is bonded in a single-bond geometry to one Ge2+ atom. In the third H+0.50- site, H+0.50- is bonded in a single-bond geometry to one Ge2+ atom. In the fourth H+0.50- site, H+0.50- is bonded in a single-bond geometry to one Ge2+ atom.
GeH4 crystallizes in the monoclinic P2_1/m space group. The structure is one-dimensional and consists of two hydrogen molecules and two GeH2 ribbons oriented in the (0, 0, 1) direction. In each GeH2 ribbon, Ge2+ is bonded in a bent 150 degrees geometry to two H+0.50- atoms. There are one shorter (2.17 Å) and one longer (2.18 Å) Ge–H bond lengths. There are two inequivalent H+0.50- sites. In the first H+0.50- site, H+0.50- is bonded in a single-bond geometry to one Ge2+ and one H+0.50- atom. The H–H bond length is 0.80 Å. In the second H+0.50- site, H+0.50- is bonded in a single-bond geometry to one Ge2+ and one H+0.50- atom.
GeH4 crystallizes in the monoclinic C2/c space group. The structure is one-dimensional and consists of four hydrogen molecules and two GeH2 ribbons oriented in the (0, 0, 1) direction. In each GeH2 ribbon, Ge2+ is bonded in a distorted rectangular see-saw-like geometry to four equivalent H+0.50- atoms. There is two shorter (1.68 Å) and two longer (2.00 Å) Ge–H bond length. H+0.50- is bonded in a water-like geometry to two equivalent Ge2+ atoms.
Metalattices are crystalline arrays of uniform particles in which the period of the crystal is close to some characteristic physical length scale of the material. In this work, we explore the synthesis and properties of a germanium metalattice in which the similar to 70 nm periodicity of a silica colloidal crystal template is close to the similar to 24 nm Bohr exciton radius of the nanocrystalline Ge replica. The problem of Ge surface oxidation can be significant when exploring quantum confinement effects or designing electronically coupled nanostructures because of the high surface area to volume ratio at the nanoscale. To eliminate surface oxidation, we developed a coreshell synthesis in which the Ge metalattice is protected by an oxide-free Si interfacial layer, and we explore its properties by transmission electron microscopy (TEM), Raman spectroscopy, and electron energy loss spectroscopy (EELS). The interstices of a colloidal crystal film grown from 69 nm diameter spherical silica particles were filled with polycrystalline Ge by high-pressure confined chemical vapor deposition (HPcCVD) from GeH4. After the SiO2 template was etched away with aqueous HF, the Ge replica was uniformly coated with an amorphous Si shell by HPcCVD as confirmed by TEM-EDS (energy-dispersive X-ray spectroscopy) and Raman spectroscopy. Formation of the shell prevents oxidation of the Ge core within the detection limit of XPS. The electronic properties of the core-shell structure were studied by accessing the Ge 3d edge onset using STEM-EELS. A blue shift in the edge onset with decreasing size of Ge sites in the metalattices suggests quantum confinement of the Ge core. The degree of quantum confinement of the Ge core depends on the void sizes in the template, which is tunable by using silica particles of varying size. The edge onset also shows a shift to higher energy near the shell in comparison with the Ge core. This shift along with the observation of Ge-Si vibrational modes in the Raman spectrum indicate interdiffusion of Ge and Si. Both the size of the voids in the template and core-shell interdiffusion of Si and Ge can in principle be tuned to modify the electronic properties of the Ge metalattice.
Novel optoelectronic device designs based on the heterostructures of III-N and II-IV-N 2 are promising to advance device performance significantly. For example, by utilizing InGaN-ZnGeN 2 quantum well (QW) structures instead of pure InGaN, the band structure engineering in the QW active region can lead to improved electron-hole wavefunction overlap, and thus enhance the radiative efficiency for photon generation. These novel heterostructures have great potential to address the current challenge of low quantum efficiency in InGaN QW based light emitting diodes emitting in green and beyond. The materials development of ZnGeN 2 is still at an early stage as compared to the much matured GaN material system. In an ideal octet rule preserving ordered structure of ZnGeN 2 , every N atom is coordinated by exactly two Zn and two Ge atoms. However, local violation of octet rule can be caused by non-ideal coordination of N by the cations. The disordered structure is thermodynamically less favorable but can still be achieved, for example, in kinetics-limited growth regime. The ordered ZnGeN 2 has a bandgap very close to that of GaN (~3.4 eV) and a lattice mismatch of <0.1% with GaN. Interestingly, the valence band of ZnGeN 2 has been predicted to be ~1 eV above that of GaN, which has inspired novel designs for high efficiency light emitters. In this work, we investigated the metalorganic chemical vapor deposition (MOCVD) of ZnGeN 2 films on GaN/c-sapphire templates. Diethylzinc (DEZn), germane (GeH4) and ammonia were used as the precursors for Zn, Ge and N, respectively. A systematic study was conducted to investigate the cation stoichiometry as a function of growth temperature (TG), total reactor pressure (P) and DEZn/GeH 4 molar flow rate ratio (RII/IV). Under the investigated growth window, the Zn/(Zn+Ge) composition in the films, determined from energy dispersive X-ray spectroscopy, decreased monotonically with increase in TG but increased with increase in P and RII/IV. Atom probe tomography data did not indicate the presence of any secondary phases such as Zn 3 N 2 or Ge 3 N 4 . The surface morphology and crystallinity of the grown films had strong correlation with the Zn/(Zn+Ge) composition. The scanning electron microscopy images showed that the near-stoichiometric films have planar surfaces whereas Zn-rich films had crystallites on their surface and the Zn-poor films had faceted surface. Scanning transmission electron microscopy (STEM) imaging revealed that the Zn-rich and Zn-poor films have columnar and filament-like morphology, respectively, whereas the near-stoichiometric films have continuous film-like cross-sectional morphology. TEM nano-diffraction patterns as well as X-ray diffraction 2θ-ω scan profiles indicate that the near stoichiometric films are single crystalline. Nano-diffraction pattern of the stoichiometric films resembled that of a disordered ZnGeN 2 structure. Room temperature Raman spectra of near-stoichiometric films showed only the phonon density of states like features of a cation disordered ZnGeN 2 . Cathodoluminescence and photoluminescence spectra measured at different temperatures had similar features with peak emission wavelength at ~ 2 eV. In conclusion, the stoichiometry of ZnGeN 2 films can be widely tuned by tuning the MOCVD growth parameters. The surface morphology and the crystallinity of the films were found to have strong correlation with the Zn/(Zn+Ge) composition. The stoichiometric ZnGeN 2 films grown on GaN were demonstrated with uniform surface morphology and high crystalline quality. The results from this work will provide pathway to implement ZnGeN 2 in device structures.