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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

A Comparative Analysis of Catalysts for the Preparation of Germanium through Hydrogen Reduction of Germanium Tetrachloride

We have synthesized catalysts for the hydrogen reduction of germanium tetrachloride: a catalyst based on multiwalled carbon nanotubes and a hybrid catalyst based on multiwalled carbon nanotubes whose surface was decorated with copper-containing nanoparticles. The hybrid catalyst has been characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results demonstrate that it consists of multiwalled carbon nanotubes whose surface is decorated with copper nanoparticles in a cuprous oxide shell (Cu{sub 2}O/Cu/MWCNTs). The catalytic activity of the hybrid catalyst exceeds that of the as-prepared MWCNTs. The use of the Cu{sub 2}O/Cu/MWCNT hybrid catalyst as a catalyst for the hydrogen reduction of germanium tetrachloride allows the reaction temperature to be lowered and ensures 95.7% germanium tetrachloride conversion at 873 K.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Characterization of high-purity germanium detectors with amorphous germanium contacts in cryogenic liquids

For the first time, planar high-purity germanium detectors with thin amorphous germanium contacts were successfully operated directly in liquid nitrogen and liquid argon in a cryostat at the Max-Planck-Institut für Physics in Munich. The detectors were fabricated at the Lawrence Berkeley National Laboratory and the University of South Dakota, using crystals grown at the University of South Dakota. They survived long-distance transportation and multiple thermal cycles in both cryogenic liquids and showed reasonable leakage currents and spectroscopic performance. Also discussed are the pros and cons of using thin amorphous semiconductor materials as an alternative contact technology in large-scale germanium experiments searching for physics beyond the Standard Model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Attosecond quantum kinetics of photoexcited Germanium

© 2017 IEEE. Attosecond transient reflectivity is developed to observe the photoexcitation dynamics in germanium. Attosecond time-resolved measurements of the dielectric function reveal a fewfemtosecond collective electronic response time, which renormalizes the Coulomb interaction between the excited carriers.

Kraus, Peter↗
NASA NTRS1979

Germanium and germanium-diamond bolometers operated at 4.2K, 2.0K, 1.2K, 0.3K and 0.1K

The design, construction, and performance of state of the art germanium and germanium-diamond bolometers operated at 4.2, 2.0, 1.2, and 0.3 K are discussed. These detectors have a broad range of applications, and are particularly important for the long wavelength (far infrared to millimeter) regions. Current results may be extrapolated to lower temperatures and higher levels of performance. A system which will operate at 0.1 K using a He-4-He-3 dilution refrigerator is under development.

Johnson, C.↗
NASA NTRS1999

Determination of the Wetting Angle of Germanium and Germanium-Silicon Melts on Different Substrate Materials

During Bridgman growth of semiconductors detachment of the crystal and the melt meniscus has occasionally been observed, mainly under microgravity (microg) conditions. An important factor for detached growth is the wetting angle of the melt with the crucible material. High contact angles are more likely to result in detachment of the growing crystal from the ampoule wall. In order to achieve detached growth of germanium (Ge) and germanium-silicon (GeSi) crystals under 1g and microg conditions, sessile drop measurements were performed to determine the most suitable ampoule material as well as temperature dependence of the surface tension for GeSi. Sapphire, fused quartz, glassy carbon, graphite, SiC, pyrolytic Boron Nitride (pBN), AIN, and diamond were used as substrates. Furthermore, different cleaning procedures and surface treatments (etching, sandblasting, etc.) of the same substrate material and their effect on the wetting behavior were studied during these experiments. pBN and AIN substrates exhibited the highest contact angles with values around 170 deg.

Kaiser, Natalie↗
NASA NTRS2001

Detached Bridgman Growth of Germanium and Germanium-Silicon Alloy Crystals

Earth based experiments on the science of detached crystal growth are being conducted on germanium and germanium-silicon alloys (2at% Si average composition) in preparation for a series of experiments aboard the International Space Station (ISS) to differentiate among proposed mechanisms contributing to detachment. Sessile drop measurements were first carried out for a large number of substrates made of potential ampoule materials to determine the contact angles and the surface tension as a function of temperature and composition. The process atmosphere and duration of the experiment (for some cases) were also found to have significant influence on the wetting angle. Growth experiments have used pyrolytic boron nitride (pBN) and fused silica ampoules with the majority of the detached results occurring predictably in the pBN. The contact angles were 173 deg (Ge) and 165 deg (GeSi) for pBN. For fused silica, the contact angle decreases to an equilibrium value with duration of measurement ranging from 150 to 117 deg (Ge), 129 to 100 deg (GeSi). Forming gas (Ar + 2% H2) and vacuum have been used in the growth ampoules. With gas in the ampoule, a variation of the temperature profile during growth has been used to control the pressure difference between the top of the melt and the volume below the melt caused by detachment of the growing crystal. The stability of detachment has been modeled and substantial insight has been gained into the reasons that detachment has most often been observed in reduced gravity but nonetheless has occurred randomly even there. An empirical model for the conditions necessary to achieve sufficient stability to maintain detached growth for extended periods has been developed and will be presented. Methods for determining the nature and extent of detachment include profilometry and optical and electron microscopy. This surface study is the subject of another presentation at this Congress. Results in this presentation will show that we have established the effects of different ampoule materials, temperature profiles, pressure differences, and silicon concentrations and that samples that are nearly completely detached can be grown repeatedly.

Szofran, F. R.↗
NASA NTRS2002

Detached Bridgman Growth of Germanium and Germanium-Silicon Alloy Crystals

Earth based experiments on the science of detached crystal growth are being conducted on germanium and germanium-silicon alloys (2 at% Si average composition) in preparation for a series of experiments aboard the International Space Station (ISS). The purpose of the microgravity experiments includes differentiating among proposed mechanisms contributing to detachment, and confirming or refining our understanding of the detachment mechanism. Because large contact angle are critical to detachment, sessile drop measurements were used to determine the contact angles as a function of temperature and composition for a large number of substrates made of potential ampoule materials. Growth experiments have used pyrolytic boron nitride (pBN) and fused silica ampoules with the majority of the detached results occurring predictably in the pBN. The contact angles were 173 deg (Ge) and 165 deg (GeSi) for pBN. For fused silica, the contact angle decreases from 150 deg to an equilibrium value of 117 deg (Ge) or from 129 deg to an equilibrium value of 100 deg (GeSi) over the duration of the experiment. The nature and extent of detachment is determined by using profilometry in conjunction with optical and electron microscopy. The stability of detachment has been analyzed, and an empirical model for the conditions necessary to achieve sufficient stability to maintain detached growth for extended periods has been developed. Results in this presentation will show that we have established the effects on detachment of ampoule material, pressure difference above and below the melt, and silicon concentration; samples that are nearly completely detached can be grown repeatedly in pBN.

Szofran, F. R.↗
DOE OSTI2018

Defect reduction by liquid phase epitaxy of germanium on single-crystalline-like germanium templates on flexible, low-cost metal substrates

Single-crystalline-like germanium (Ge) templates were demonstrated on low-cost, flexible metal substrates and have been used to fabricate III–V materials and devices for photovoltaics and flexible electronics applications. However, these Ge templates, fabricated by magnetron sputtering or plasma enhanced chemical vapor deposition, contain a high density of defects. In order to improve the performance of optoelectronic devices made using the Ge templates, a homo-epitaxial Ge layer has been additionally grown by a liquid phase epitaxy (LPE) method. The LPE Ge layer is composed of significantly larger grains (~26 μm) compared to that of the Ge template (~200 nm). This large size of the LPE Ge grains effectively reduces the volume fraction of grain boundaries. The LPE Ge shows an out-of-plane texture Δω of ~0.63° and an in-plane texture ΔΦ of ~1.26°, which signify improvements of ~39.3% and ~76.6% compared to that of the vapor-deposited Ge template, respectively. Further, the LPE Ge is strain free, compared to the strained Ge template hetero-epitaxially grown on cerium oxide. Defects caused by low-angle grain boundaries, impurities and strain relaxation in the Ge template are found to be suppressed in the LPE Ge. The threading dislocation density is roughly estimated to be ~5 × 10 6 cm -2 in the LPE Ge compared to ~1 × 10 10 cm -2 in the Ge template.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Response of Waveguide-Integrated Germanium-on-Silicon p-i-n Photodiodes to Neutron Displacement Damage

The effects of 14-MeV neutron displacement damage (DD) on waveguide-integrated germanium-on-silicon p-i-n photodiodes (PDs) for silicon photonics have been investigated up to fluences of 7.5×1012 n/cm2 (14 MeV), or 1.4×1013 n1-MeVeq/cm2(Si). The study includes measurements of dark current-voltage characteristics across temperature from 150-375 K, measurements of PD junction capacitance, spectral response measurements from 1260 nm to 1360 nm, and frequency response measurements. The devices are found to be susceptible to DD-induced carrier removal effects; however, they also continue to operate without meaningful impact to performance for the DD dose levels examined. Since the PD test chips include silicon photonic integrated grating couplers and waveguides which carry the optical signal to the PD, some assessment of the impact of DD on these passive devices can also be inferred. Finally, this work does not examine the short-term annealing or transient behavior of the DD, and instead has only considered the lasting damage that remains after any initial period of room temperature annealing.

42 ENGINEERING↗
DOE OSTI2020

Investigation of the electrical conduction mechanisms in P-type amorphous germanium electrical contacts for germanium detectors in searching for rare-event physics

For the first time, electrical conduction mechanisms in the disordered material system is experimentally studied for p-type amorphous germanium (a-Ge) used for high-purity Ge detector contacts. The localization length and the hopping parameters in a-Ge are determined using the surface leakage current measured from three high-purity planar Ge detectors. The temperature dependent hopping distance and hopping energy are obtained for a-Ge fabricated as the electrical contact materials for high-purity Ge planar detectors. As a result, we find that the hopping energy in a-Ge increases as temperature increases while the hopping distance in a-Ge decreases as temperature increases. The localization length of a-Ge is on the order of 2.13$^{-0.05}_{+0.07}$A° to 5.07$^{0.83}_{+2.58}$A°,depending on the density of states near the Fermi energy level within bandgap. Using these parameters, we predict that the surface leakage current from a Ge detector with a-Ge contacts can be much smaller than one yocto amp (yA) at helium temperature, suitable for rare-event physics searches.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Phase Transitions in Amorphous Germanium under Non-Hydrostatic Compression

As the pioneer semiconductor in transistor, germanium (Ge) has been widely applied in information technology for over half a century. Although many phase transitions in Ge have been reported, the complicated phenomena of the phase structures in amorphous Ge under extreme conditions are still not fully investigated. Here, we report the different routes of phase transition in amorphous Ge under different compression conditions utilizing diamond anvil cell (DAC) combined with synchrotron-based X-ray diffraction (XRD) and Raman spectroscopy techniques. Upon non-hydrostatic compression of amorphous Ge, we observed that shear stress facilitates a reversible pressure-induced phase transformation, in contrast to the pressure-quenchable structure under a hydrostatic compression. These findings afford better understanding of the structural behaviors of Ge under extreme conditions, which contributes to more potential applications in the semiconductor field.

Xu, Jianing (ORCID:0000000325474344)↗