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All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Modeling and Simulation of Electrostatics of Ge$_{\text{1-x}}$Sn$_{\text{x}}$ Layers Grown on Ge Substrates

This work introduces a comprehensive simulation tool that provides a robust 1D Schrödinger – Poisson solver for modeling the electrostatics of heterostructures with an arbitrary number of layers, and non-uniform doping profiles along with the treatment of partial ionization of dopants at low temperatures. The effective masses are derived from the first-principles calculations. The solver is used to characterize three Ge 1-x Sn x /Ge heterostructures with non-uniform doping profiles and determine the subband structure at various temperatures. Here, the simulation results of the sheet carrier densities show excellent agreement with the experimentally extracted data, thus demonstrating the capabilities of the solver.

42 ENGINEERING↗
DOE OSTI2026

Strain Relaxation and Relative Defect Density with Thickness in MBE-Grown Ge 0.85 Sn 0.15 on Ge(001)

Germanium–tin (GeSn) alloys are emerging as promising materials for mid-infrared optoelectronics and silicon-compatible photonic devices, owing to their tunable direct bandgap. However, the growth of high-quality GeSn films with high Sn content remains challenging due to strain-induced defect formation. In this study, we investigate the role of film thickness on strain-induced relaxation, defect density, and Sn segregation. A series of five samples with varying thicknesses and ∼15% Sn-containing GeSn layers were grown, ranging from the critical thickness for strain relaxation to the onset of Sn segregation. All GeSn samples were analyzed using X-ray diffraction reciprocal space mapping (XRD-RSM) to explore the evolution of strain-induced relaxation as a function of thickness. Photoluminescence measurements reveal that increasing the GeSn thickness enhances strain relaxation while reducing defect-related emission, indicating a decrease in effective defect density prior to reaching the threshold thickness of GeSn layer. At a thickness of ∼150 nm, the GeSn layer shows the onset of Sn segregation, evident in the XRD-RSM spectrum, marking the threshold thickness for Sn segregation. This work defines an effective growth window in terms of thickness (35 to 150 nm) for fabricating relaxed, defect-suppressed GeSn layers with 15% Sn content. These findings emphasize the crucial role of thickness control in balancing strain relaxation and defect suppression, advancing the fabrication of high-quality, high Sn-content relaxed GeSn using molecular beam epitaxy.

Defects↗
DOE OSTI2020

Materials Data on Ge(TePd4)2 by Materials Project

Ge(Pd4Te)2 crystallizes in the trigonal R3c space group. The structure is three-dimensional. there are eight inequivalent Pd sites. In the first Pd site, Pd is bonded in a 3-coordinate geometry to six Pd, one Ge, and two equivalent Te atoms. There are a spread of Pd–Pd bond distances ranging from 2.84–3.36 Å. The Pd–Ge bond length is 2.61 Å. There are one shorter (2.70 Å) and one longer (2.78 Å) Pd–Te bond lengths. In the second Pd site, Pd is bonded in a 3-coordinate geometry to six Pd and three Te atoms. There are a spread of Pd–Pd bond distances ranging from 2.86–3.24 Å. There are a spread of Pd–Te bond distances ranging from 2.70–2.79 Å. In the third Pd site, Pd is bonded in a 4-coordinate geometry to three equivalent Pd, one Ge, and three equivalent Te atoms. All Pd–Pd bond lengths are 3.09 Å. The Pd–Ge bond length is 2.58 Å. All Pd–Te bond lengths are 2.82 Å. In the fourth Pd site, Pd is bonded in a 1-coordinate geometry to seven Pd, one Ge, and three equivalent Te atoms. There are three shorter (2.82 Å) and one longer (2.87 Å) Pd–Pd bond lengths. The Pd–Ge bond length is 2.50 Å. All Pd–Te bond lengths are 2.86 Å. In the fifth Pd site, Pd is bonded in a 4-coordinate geometry to nine Pd, one Ge, and three equivalent Te atoms. All Pd–Pd bond lengths are 3.08 Å. The Pd–Ge bond length is 2.59 Å. All Pd–Te bond lengths are 2.81 Å. In the sixth Pd site, Pd is bonded in a 11-coordinate geometry to seven Pd and four Te atoms. All Pd–Pd bond lengths are 2.90 Å. There are one shorter (2.64 Å) and three longer (2.80 Å) Pd–Te bond lengths. In the seventh Pd site, Pd is bonded in a 2-coordinate geometry to nine Pd, two Ge, and two Te atoms. There are a spread of Pd–Pd bond distances ranging from 2.80–3.17 Å. There are one shorter (2.55 Å) and one longer (2.66 Å) Pd–Ge bond lengths. There are one shorter (2.84 Å) and one longer (2.92 Å) Pd–Te bond lengths. In the eighth Pd site, Pd is bonded in a 1-coordinate geometry to nine Pd, two Ge, and two Te atoms. There are one shorter (2.55 Å) and one longer (2.81 Å) Pd–Ge bond lengths. There are one shorter (2.69 Å) and one longer (2.93 Å) Pd–Te bond lengths. There are two inequivalent Ge sites. In the first Ge site, Ge is bonded in a 10-coordinate geometry to ten Pd atoms. In the second Ge site, Ge is bonded in a body-centered cubic geometry to eight Pd atoms. There are two inequivalent Te sites. In the first Te site, Te is bonded in a distorted q6 geometry to ten Pd atoms. In the second Te site, Te is bonded in a 10-coordinate geometry to ten Pd atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Impact of Arsenic- and Indium-Terminated InGaAs Stressors on Carrier Confinement, Strain, Defects, and Transport Properties of Tensile-Strained Ge

Device-quality tensile-strained Ge (ε-Ge) grown on a large bandgap semiconductor with superior electrical and optical carrier confinement is essential for group-IV-based optoelectronics. Properties of ε-Ge active layers synthesized on In 0.24 Ga 0.76 As buffers with two different surface terminations─arsenic-rich and indium-rich─were experimentally demonstrated, highlighting the factors not considered in theoretical calculations. High-resolution X-ray diffraction and Raman spectroscopy analyses of these ε-Ge/In 0.24 Ga 0.76 As heterostructures confirmed the fully strained (1.6%) and partially relaxed (0.82%) nature of the ε-Ge bonded with arsenic-terminated (Ge As-terminated ) and indium-terminated (Ge In-terminated ) In 0.24 Ga 0.76 As stressors, respectively. High-resolution cross-sectional transmission electron microscopy showed a coherent, sharp, and fully strained ε-Ge/In 0.24 Ga 0.76 As heterointerface in the Ge As-terminated heterostructure, whereas microtwin defects were present in the Ge In-terminated heterostructure. These heterostructures were further characterized by evaluating the minority carrier lifetimes, high for Ge As-terminated (525 ns) and low for Ge In-terminated (69 ns), using the photoconductive decay technique. Moreover, band alignment was constructed using X-ray photoelectron spectroscopy, where the Ge As-terminated heterostructure revealed that both holes and electrons were confined within the ε-Ge active layer as a type-I band alignment with ΔE V, As-terminated = 0.22 eV and ΔE C,As-terminated = 0.38 eV. On the other hand, the Ge In-terminated heterostructure exhibited a type-II band alignment with ΔE V,In-terminated = – 0.02 eV and ΔE C,In-terminated = 0.53 eV. Furthermore, the magnetotransport properties revealed high mobility (321 cm 2 /(V s)) with single-electron transport in Ge As-terminated heterostructure and low mobility (3.34 cm 2 /(V s)) with multihole transport in the Ge In-terminated heterostructure. Therefore, preferring the ε-Ge on the arsenic-rich surface of In 0.24 Ga 0.76 As stressor over the indium-rich surface during material synthesis offers device-quality materials with high carrier lifetime and superior carrier confinement, which can provide an opportunity to fabricate efficient group-IV-based optoelectronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ge by Materials Project

Ge is Clathrate-like structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. there are three inequivalent Ge sites. In the first Ge site, Ge is bonded to four equivalent Ge atoms to form corner-sharing GeGe4 tetrahedra. All Ge–Ge bond lengths are 2.47 Å. In the second Ge site, Ge is bonded to four Ge atoms to form corner-sharing GeGe4 tetrahedra. All Ge–Ge bond lengths are 2.49 Å. In the third Ge site, Ge is bonded to four Ge atoms to form corner-sharing GeGe4 tetrahedra. There are two shorter (2.49 Å) and one longer (2.52 Å) Ge–Ge bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ge by Materials Project

Ge crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. there are three inequivalent Ge sites. In the first Ge site, Ge is bonded in a tetrahedral geometry to four equivalent Ge atoms. All Ge–Ge bond lengths are 2.81 Å. In the second Ge site, Ge is bonded to four Ge atoms to form corner-sharing GeGe4 tetrahedra. All Ge–Ge bond lengths are 2.48 Å. In the third Ge site, Ge is bonded in a distorted see-saw-like geometry to four Ge atoms. There are two shorter (2.50 Å) and one longer (2.60 Å) Ge–Ge bond lengths.

36 MATERIALS SCIENCE↗
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↗
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↗