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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Ge by Materials Project

Ge is BC8 structured and crystallizes in the trigonal R-3 space group. The structure is three-dimensional. there are two inequivalent Ge sites. In the first Ge site, Ge is bonded to four Ge atoms to form corner-sharing GeGe4 trigonal pyramids. There are three shorter (2.53 Å) and one longer (2.56 Å) Ge–Ge bond lengths. In the second Ge site, Ge is bonded to four Ge atoms to form corner-sharing GeGe4 trigonal pyramids. There are one shorter (2.50 Å) and two longer (2.54 Å) Ge–Ge bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ge by Materials Project

Ge crystallizes in the tetragonal P4_32_12 space group. The structure is three-dimensional. there are two inequivalent Ge sites. In the first Ge site, Ge is bonded to four equivalent Ge atoms to form distorted corner-sharing GeGe4 tetrahedra. There are two shorter (2.52 Å) and two longer (2.53 Å) Ge–Ge bond lengths. In the second Ge site, Ge is bonded in a rectangular see-saw-like geometry to four Ge atoms. Both Ge–Ge bond lengths are 2.55 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ge by Materials Project

Ge crystallizes in the orthorhombic Fmmm space group. The structure is three-dimensional. there are two inequivalent Ge sites. In the first Ge site, Ge is bonded in a 6-coordinate geometry to six Ge atoms. There are a spread of Ge–Ge bond distances ranging from 2.71–2.96 Å. In the second Ge site, Ge is bonded to five Ge atoms to form a mixture of distorted edge and corner-sharing GeGe5 trigonal bipyramids. There are one shorter (2.61 Å) and two longer (2.64 Å) Ge–Ge bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ge by Materials Project

Ge is diamond-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are two inequivalent Ge sites. In the first Ge site, Ge is bonded to four Ge atoms to form corner-sharing GeGe4 tetrahedra. There are one shorter (2.47 Å) and three longer (2.50 Å) Ge–Ge bond lengths. In the second Ge site, Ge is bonded to four Ge atoms to form corner-sharing GeGe4 tetrahedra. The Ge–Ge bond length is 2.50 Å.

36 MATERIALS SCIENCE↗
NASA NTRS1995

Characterization of High Ge Content SiGe Heterostructures and Graded Alloy Layers Using Spectroscopic Ellipsometry

Si(x)Ge(1-x)heterostructures on Si substrates have been widely studied due to the maturity of Si technology. However, work on Si(x)Ge)1-x) heterostructures on Ge substrates has not received much attention. A Si(x)Ge(1-x) layer on a Si substrate is under compressive strain while Si(x)Ge(1-x) on Ge is under tensile strain; thus the critical points will behave differently. In order to accurately characterize high Ge content Si(x)Ge(1-x) layers the energy shift algorithm used to calculate alloy compositions, has been modified. These results have been used along with variable angle spectroscopic ellipsometry (VASE) measurements to characterize Si(x)Ge(1-x)/Ge superlattices grown on Ge substrates. The results agree closely with high resolution x-ray diffraction measurements made on the same samples. The modified energy shift algorithm also allows the VASE analysis to be upgraded in order to characterize linearly graded layers. In this work VASE has been used to characterize graded Si(x)Ge(1-x) layers in terms of the total thickness, and the start and end alloy composition. Results are presented for a 1 micrometer Si(x)Ge(1-x) layer linearly graded in the range 0.5 less than or equal to x less than or equal to 1.0.

Heyd, A. R.↗
DOE OSTI2024

Elucidating the Role of InGaAs and InAlAs Buffers on Carrier Dynamics of Tensile-Strained Ge Double Heterostructures

Extensive research efforts of strained germanium (Ge) are currently underway due to its unique properties, namely, (i) possibility of band gap and strain engineering to achieve a direct band gap, thus exhibiting superior radiative properties, and (ii) higher electron and hole mobilities than Si for upcoming technology nodes. Realizing lasing structures is vital to leveraging the benefits of tensile-strained Ge (ε-Ge). Here, we use a combination of different analytical tools to elucidate the effect of the underlying InGaAs/InAlAs and InGaAs overlaying heterostructures on the material quality and strain state of ε-Ge grown by molecular beam epitaxy. Using X-ray analysis, we show the constancy of tensile strain in sub-50 nm ε-Ge in a quantum-well (QW) heterostructure. Further, effective carrier lifetime using photoconductive decay as a function of buffer type exhibited a high (low) defect-limited carrier lifetime of ~68 ns (~13 ns) in 0.61% (0.66%) ε-Ge grown on an InGaAs (InAlAs) buffer. These results correspond well with the measured surface roughness of 1.289 nm (6.303 nm), consistent with the surface effect of the ε-Ge/III–V heterointerface. Furthermore, a reasonably high effective lifetime of ~78 ns is demonstrated in a QW of ~30 nm 1.6% ε-Ge, a moderate reduction from ~99 ns in uncapped ε-Ge, alluding to the surface effect of the overlying heterointerface. Thus, the above results highlight the prime quality of ε-Ge that can be achieved via III–V heteroepitaxy and paves a path for integrated Ge photonics.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Complex Dirac-like Electronic Structure in Atomic Site-Ordered Rh 3 In 3.4 Ge 3.6

We report the synthesis via an indium flux method of a novel single-crystalline compound Rh 3 In 3.4 Ge 3.6 that belongs to the cubic Ir 3 Ge 7 structure type. In Rh 3 In 3.4 Ge 3.6 , the In and Ge atoms preferentially occupy, respectively, the 12d and 16f sites of the Im3¯m space group, thus creating a colored variant of the Ir 3 Ge 7 structure. Like the other compounds of the Ir 3 Ge 7 family, Rh 3 In 3.4 Ge 3.6 shows potential as a thermoelectric, displaying a relatively large power factor, PF ~ 2 mW/cm K 2 , at a temperature T ~ 225 K, albeit showing a modest figure of merit, ZT = 8 x 10 -4 , because of the lack of a finite band gap. These figures might improve through a use of chemical substitution strategies to achieve band gap opening. Remarkably, electronic band structure calculations reveal that this compound displays a complex Dirac-like electronic structure relatively close to the Fermi level. The electronic structure is composed of several Dirac type-I and type-II nodes, and even Dirac type-III nodes that result from the touching between a flat band and a linearly dispersing band. Here, this rich Dirac-like electronic dispersion suggests the possibility to observe experimentally Dirac type-III nodes and study their role in the physical properties of Rh 3 In 3.4 Ge 3.6 and related Ir 3 Ge 7 -type materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Halide Vapor Phase Epitaxy of Ge from an Elemental Source

Halide vapor phase epitaxy shows promise for low-cost photovoltaic device manufacturing because of its high growth rates and lower cost elemental precursors but previously has not been used to deposit epitaxial Ge. Here, we demonstrate Ge deposition by generating GeCl 2 in situ from solid Ge and HCl in a N 2 ambient. To achieve Ge growth, we inject AsH 3 and PH 3 as sources of active hydrogen to the growth surface to create a driving force for growth. We do not observe Ge growth unless a supply of hydrogen is added, consistent with thermodynamic calculations. Furthermore, we show the hydrogen source must crack readily on the substrate surface to enable growth; relatively stable sources such as H 2 do not cause growth. Unintentional group V doping is one drawback of using AsH 3 and PH 3 to drive the Ge reaction. We observed As or P concentrations in the Ge films ranging from 4 x 10 17 to 1 x 10 18 atoms/cm 3 , concentrations that can drastically influence device characteristics. However, we note there are numerous other "helper molecule" options that can provide active hydrogen without doping or etching the material. This work provides a path forward for Ge deposition for optoelectronic devices from an elemental source.

14 SOLAR ENERGY↗
DOE OSTI2024

Characterization of Mn 5 Ge 3 Contacts on a Shallow Ge/SiGe Heterostructure

Mn 5 Ge 3 is a ferromagnetic phase of the Mn-Ge system that is a potential contact material for efficient spin injection and detection. Here, we investigate the creation of Mn 5 Ge 3 -based contacts on a Ge/SiGe quantum well heterostructure via solid-state synthesis. X-ray diffraction spectra fitting indicates the formation of Mn 5 Ge 3 -based contacts on bulk Ge and Ge/SiGe. High-resolution scanning transmission electron microscopy imaging and energy dispersive X-ray spectroscopy verify the correct Mn 5 Ge 3 -based phase formation. Schottky diode measurements, transmission line measurements, and Hall measurements reveal that Mn 5 Ge 3 -based contacts serve as good p-type contacts for Ge/SiGe quantum well heterostructures due to having a low Schottky barrier height of 0.10 eV (extracted from a Mn 5 Ge 3 /n-Ge analogue) and a contact resistance in the order of 1 kΩ. Furthermore, we show that these electrical characteristics have a gate-voltage dependence, thereby providing tunability.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ge(BrF5)2 by Materials Project

Ge(BrF5)2 crystallizes in the monoclinic P2_1/c space group. The structure is one-dimensional and consists of two Ge(BrF5)2 ribbons oriented in the (1, 0, 0) direction. Ge is bonded in an octahedral geometry to six F atoms. There is two shorter (1.76 Å) and four longer (1.89 Å) Ge–F bond length. Br is bonded in a rectangular see-saw-like geometry to four F atoms. There are a spread of Br–F bond distances ranging from 1.78–2.20 Å. There are five inequivalent F sites. In the first F site, F is bonded in a single-bond geometry to one Br atom. In the second F site, F is bonded in a single-bond geometry to one Br atom. In the third F site, F is bonded in a distorted bent 120 degrees geometry to one Ge and one Br atom. In the fourth F site, F is bonded in a distorted bent 120 degrees geometry to one Ge and one Br atom. In the fifth F site, F is bonded in a single-bond geometry to one Ge atom.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Single crystal growth and thermoelectric properties of Nowotny chimney-ladder compound Fe 2 Ge 3

Fe 2 Ge 3 with an incommensurate Nowotny chimney-ladder (NCL) structure is a promising material for thermoelectric applications due to its low thermal conductivity. Previous experimental studies on Fe 2 Ge 3 have mainly focused on polycrystalline samples, resulting in a limited understanding of the material's intrinsic thermoelectric properties and the underlying causes of its low thermal conductivity. Here we report the synthesis and thermoelectric properties of single crystalline Fe 2 Ge 3 . Millimeter-sized Fe 2 Ge 3 single crystals grown by the chemical vapor transport method enable the study of the intrinsic thermoelectric properties. The Seebeck coefficient of Fe 2 Ge 3 is negative and its magnitude increases linearly with temperature, showing a degenerate n-type semiconductor behavior. Analysis of the electrical resistivity and specific heat data indicates the existence of an Einstein mode with a characteristic temperature of about 60 K, suggesting the presence of low-energy optical phonons. Further, the thermal conductivity of Fe 2 Ge 3 along the c axis is as low as 1.9Wm -1 K -1 at 300 K and exhibits a nearly temperature-independent characteristic, which is distinct from the previous theoretical calculations with a stronger temperature dependence. The low thermal conductivity may be attributed to the scattering of acoustic phonons by low-energy optical modes and the presence of non-extended diffuson modes, as reported in another NCL compound, MnSi 1.74 . This study provides valuable insights into the electrical and thermal properties of Fe 2 Ge 3 , which can open up possibilities for future advances in thermoelectric applications.

36 MATERIALS SCIENCE↗
NASA NTRS1984

Ge abundances in the lunar mantle and implications for the origin of the Moon

Regardless of the origin of the Moon, metal segregation must have occurred within the moon in order to account for its low siderophile element abundances relative to the Earth or chondrites. Germanium is a strongly siderophile element whose bulk distribution coefficient indicates that it is not fractionated during igneous processes on the Moon. The variability in absolute Ge abundances in mare basalts and pristine highland rocks, rather than elemental ratios, can be used to infer lunar mantle abundances and processes. Literature data have been compiled for Ge abundances in mare basalts and pristine highland rocks. For some landing sites, samples with 12 ppb Ge were considered to be extreme outliers and are not included. The Apollo 15 samples are enriched in Ge by a factor of 2.5 over the Apollo 12, 16 and 17 samples. Other siderophile element variations have been found in the Moon. Based on this data, best estimate of the average Ge abundance in the silicate portion of the Moon is 3.52 ppb. The Moon is depleted, relative to chondritic abundances, by a factor of 38,000 normalized to Si. Two possible explanations for the observed variations in Ge abundance in the Moon are: (1) more metal may have segregated from some regions of the Moon than from others; or Ge-bearing material may been been added later in the evolution of the Moon.

Dickinson, T.↗
NASA NTRS1990

Possibilities for LWIR detectors using MBE-grown Si(/Si(1-x)Ge(x) structures

Traditionally, long wavelength infrared (LWIR) detection in Si-based structures has involved either extrinsic Si or Si/metal Schottky barrier devices. Molecular beam epitaxially (MBE) grown Si and Si/Si(1-x)Ge(x) heterostructures offer new possibilities for LWIR detection, including sensors based on intersubband transitions as well as improved conventional devices. The improvement in doping profile control of MBE in comparison with conventional chemical vapor deposited (CVD) Si films has resulted in the successful growth of extrinsic Si:Ga, blocked impurity-band conduction detectors. These structures exhibit a highly abrupt step change in dopant profile between detecting and blocking layers which is extremely difficult or impossible to achieve through conventional epitaxial growth techniques. Through alloying Si with Ge, Schottky barrier infrared detectors are possible, with barrier height values between those involving pure Si or Ge semiconducting materials alone. For both n-type and p-type structures, strain effects can split the band edges, thereby splitting the Schottky threshold and altering the spectral response. Measurements of photoresponse of n-type Au/Si(1-x)Ge(x) Schottky barriers demonstrate this effect. For intersubband multiquntum well (MQW) LWIR detection, Si(1-x)Ge(x)/Si detectors grown on Si substrates promise comparable absorption coefficients to that of the Ga(Al)As system while in addition offering the fundamental advantage of response to normally incident light as well as the practical advantage of Si-compatibility. Researchers grew Si(1-x)Ge(x)/Si MQW structures aimed at sensitivity to IR in the 8 to 12 micron region and longer, guided by recent theoretical work. Preliminary measurements of n- and p-type Si(1-x)Ge(x)/Si MQW structures are given.

Hauenstein, Robert J.↗
NASA NTRS1994

P/N InP solar cells on Ge wafers

Indium phosphide (InP) P-on-N one-sun solar cells were epitaxially grown using a metalorganic chemical vapor deposition process on germanium (Ge) wafers. The motivation for this work is to replace expensive InP wafers, which are fragile and must be thick and therefore heavy, with less expensive Ge wafers, which are stronger, allowing use of thinner, lighter weight wafers. An intermediate InxGs1-xP grading layer starting as In(0.49)Ga(0.51) at the GaAs-coated Ge wafer surface and ending as InP at the top of the grading layer (backside of the InP cell) was used to attempt to bend some of the threading dislocations generated by lattice-mismatch between the Ge wafer and InP cell so they would be harmlessly confined in this grading layer. The best InP/Ge cell was independently measured by NASA-Lewis with a one-sun 25 C AMO efficiently measured by NASA-Lewis with a one-circuit photocurrent 22.6 mA/sq cm. We believe this is the first published report of an InP cell grown on a Ge wafer. Why get excited over a 9 percent InP/Ge cell? If we look at the cell weight and efficiency, a 9 percent InP cell on an 8 mil Ge wafer has about the same cell power density, 118 W/kg (BOL), as the best InP cell ever made, a 19 percent InP cell on an 18 mil InP wafer, because of the lighter Ge wafer weight. As cell panel materials become lighter, the cell weight becomes more important, and the advantage of lightweight cells to the panel power density becomes more important. In addition, although InP/Ge cells have a low beginning-of-life (BOL) efficiency due to dislocation defects, the InP/Ge cells are very radiation hard (end-of-life power similar to beginning-of-life). We have irradiated an InP/Ge cell with alpha particles to an equivalent fluence of 1.6 x 10(exp 16) 1 MeV electrons/sq cm and the efficiency is still 83 percent of its BOL value. At this fluence level, the power output of these InP/Ge cells matches the GaAs/Ge cell data tabulated in the JPL handbook. Data are presented indicating InP/Ge has more power output than GaAs/Ge cells at fluences in excess of this value.

Wojtczuk, Steven↗
DOE OSTI2020

Unidirectional growth of graphene nano-islands from carbon cluster seeds on Ge(1 1 0)

The anisotropic twofold symmetry of Ge(1 1 0) makes it a unique substrate for the growth of single-crystalline graphene. However, the underlying mechanism during the initial stage of growth of graphene on Ge(1 1 0) surface is not well understood. Here, we use in-situ cryogenic scanning tunneling microscopy (STM) and spectroscopy (STS), to study the initial growth properties of graphene synthesized on Ge(1 1 0) surface with ethylene precursor gases. The STM results reveal that the unidirectional growth of the graphene nanoribbons (GNRs) initiates from carbon cluster seeds on terraces during the early stage of the growth. The orientations of the GNRs show the same directions which are nearly parallel to the direction of the Ge(1 1 0) surface. This orientation is the same as that of the wafer-scale graphene grown on Ge(1 1 0). Subsequent growth, transformed the GNRs to graphene nanoislands (GNIs), which eventually coalesced to form single crystalline monolayer graphene. STS measurements demonstrated that the GNRs have small bandgaps induced by the confinement effect of graphene. Furthermore, this study provides an in-depth understanding of the growth mechanism of graphene on Ge(1 1 0) surface in various synthesis conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2022

The Diffusion Mechanism of Ge During Oxidation of Si/SiGe Nanofins

A recently discovered, enhanced Ge diffusion mechanism along the oxidizing interface of Si/SiGe nanostructures has enabled the formation of single-crystal Si nanowires and quantum dots embedded in a defect-free, single-crystal SiGe matrix. Here, we report oxidation studies of Si/SiGe nanofins aimed at gaining a better understanding of this novel diffusion mechanism. Here, a superlattice of alternating Si/Si 0.7 Ge 0.3 layers was grown and patterned into fins. After oxidation of the fins, the rate of Ge diffusion down the Si/SiO 2 interface was measured through the analysis of HAADF-STEM images. The activation energy for the diffusion of Ge down the sidewall was found to be 1.1 eV, which is less than one-quarter of the activation energy previously reported for Ge diffusion in bulk Si. Through a combination of experiments and DFT calculations, we propose that the redistribution of Ge occurs by diffusion along the Si/SiO 2 interface followed by a reintroduction into substitutional positions in the crystalline Si.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ge by Materials Project

Ge is graphite structured and crystallizes in the hexagonal P6_3mc space group. The structure is two-dimensional and consists of two Ge sheets oriented in the (0, 0, 1) direction. Ge is bonded in a trigonal non-coplanar geometry to three equivalent Ge atoms. All Ge–Ge bond lengths are 2.44 Å.

36 MATERIALS SCIENCE↗
NASA NTRS1994

Si 1-X Ge X /Si Heterojunction Internal Photoemission Long Wavelength Infrared Detector

Long wavelength Si 1-X Ge X /Si heterojunction internal photoemission (HIP) infrared detectors have been successfully demonstrated utilizing the growth of degenerately boron doped Si 1-X Ge X layers on Si. Recently, Si 0.7 GE 0.3 /SI HIP detectors with either a Si 1-X Ge X single layer or a Si 1-X Ge X /Si multilayer have been demonstrated with cutoff wavelengths out to 23 µm. Near-ideal thermionic emission dark current characteristics were measured and the electrical potential barriers were determined by the Richardson plot. A photoresponse model, similar to the modified Fowler Equation has been developed for the Si 1-X Ge X /Si heterojunction internal photoemission infrared detector at wavelengths corresponding to photon energies less than the Fermi energy. The optical potential barriers, the corresponding cutoff wavelengths, and the emission coefficients, C 1 , for the HIP detectors have been determined from the measured spectral responses using the photoresponse model. Similar optical and thermal potential barriers were obtained.

infrared↗