Position-Dependent Transport of n-p-n Junctions in Axially Doped SiGe Nanowire Transistors.
Abstract not provided.
Delker, Collin James↗
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Results for “SiGe”
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Sensitized Near-Infrared Emission of SiGe Nanocrystals via Heterostructuring with Quasi Two-Dimensional Perovskite
The near-infrared (NIR) emission of silicon–germanium alloy nanocrystals (SiGe NCs) was sensitized by heterostructuring with a quasi two-dimensional (Q-2D) perovskite (CsPbBr 3 blended with butylammonium bromide (BABr)). Colloidal SiGe NCs were synthesized by using a nonthermal plasma method with chloride precursors. As-synthesized SiGe NCs showed no detectable photoluminescence (PL). Embedding the SiGe NCs within the perovskite matrix via spin coating led to a heterostructure exhibiting dual emissions: green emission at 520 nm from the perovskite and NIR emission at 1035 nm from the SiGe NCs. Time-integrated and resolved PL measurements and transient absorption spectroscopy revealed energy transfer from the perovskite to the SiGe NCs, which sensitized the NIR emission from the SiGe NCs and quenched the green PL for the perovskite. These results demonstrate that Ge alloying can effectively tune the bandgap of Si NCs and highlight the feasibility of heterostructuring perovskites and photoluminescent NCs to enhance or activate their PL. In conclusion, this approach broadens their potential applications in the NIR region.
36 MATERIALS SCIENCE↗
Phosphorus diffusion and deactivation during SiGe oxidation
Dopant profiles near the semiconductor–oxide interface are critical for microelectronic device performance. As the incorporation of Si 1−x Ge x into transistors continues to increase, it is necessary to understand the behavior of dopants in Si 1−x Ge x . In this paper, the diffusion and electrical activation of phosphorus within a strained, single-crystal Si 0.7 Ge 0.3 layer on Si during oxidation are reported. Both layers were uniformly doped, in situ, with an average phosphorus concentration of 4 × 10 19 atoms/cm 3 . After high-temperature oxidation, secondary ion mass spectrometry measurements revealed that the bulk of the phosphorus diffuses out of only the SiGe layer and segregates at the oxidizing SiGe–SiO 2 interface. Hall effect measurements corroborate the observed phosphorus loss and show that the phosphorus diffusing to the oxidizing interface is electrically inactive. Through density functional theory (DFT) calculations, it is shown that phosphorus interstitials prefer sites near the SiGe–SiO 2 interface. Finally, based on a combination of experimental data and DFT calculations, we propose that the phosphorus atoms are displaced from their lattice sites by Ge interstitials that are generated during SiGe oxidation. The phosphorus atoms then migrate toward the SiGe–SiO 2 interface through a novel mechanism of hopping between Ge sites as P–Ge split interstitials. Once they reach the interface, they are electrically inactive, potentially in the form of interstitial clusters or as part of the reconstructed interface or oxide.
Thornton, Chappel S.↗
Selective amorphization of SiGe in Si/SiGe nanostructures via high energy Si+ implant
Here, the selective amorphization of SiGe in Si/SiGe nanostructures via a 1 MeV Si + implant was investigated, resulting in single-crystal Si nanowires (NWs) and quantum dots (QDs) encapsulated in amorphous SiGe fins and pillars, respectively. The Si NWs and QDs are formed during high-temperature dry oxidation of single-crystal Si/SiGe heterostructure fins and pillars, during which Ge diffuses along the nanostructure sidewalls and encapsulates the Si layers. The fins and pillars were then subjected to a 3 × 10 15 ions/cm 2 1 MeV Si + implant, resulting in the amorphization of SiGe, while leaving the encapsulated Si crystalline for larger, 65-nm wide NWs and QDs. Interestingly, the 26-nm diameter Si QDs amorphize, while the 28-nm wide NWs remain crystalline during the same high energy ion implant. This result suggests that the Si/SiGe pillars have a lower threshold for Si-induced amorphization compared to their Si/SiGe fin counterparts. However, Monte Carlo simulations of ion implantation into the Si/SiGe nanostructures reveal similar predicted levels of displacements per cm 3 . Molecular dynamics simulations suggest that the total stress magnitude in Si QDs encapsulated in crystalline SiGe is higher than the total stress magnitude in Si NWs, which may lead to greater crystalline instability in the QDs during ion implant. The potential lower amorphization threshold of QDs compared to NWs is of special importance to applications that require robust QD devices in a variety of radiation environments.
36 MATERIALS SCIENCE↗
Direct growth of crystalline SiGe nanowires on superconducting NbTiN thin films
Novel heterostructures created by coupling one-dimensional semiconductor nanowires with a superconducting thin film show great potential toward next-generation quantum computing. Here, by growing high-crystalline SiGe nanowires on a NbTiN thin film, the resulting heterostructure exhibits Ohmic characteristics as well as a shift of the superconducting transition temperature (T c ). The structure was characterized at atomic resolution showing a sharp SiGe/NbTiN interface without atomic interdiffusion. Lattice spacing, as calculated from large-area x-ray diffraction experiments, suggests a potential preferred d-spacing matching between (200) NbTiN and (110) SiGe grains. The observed out-of-plane compressive strain within the NbTiN films coupled with SiGe nanowires explains the downward shift of the superconductivity behavior. The presented results post scientific insights toward functional heterostructures by coupling multi-dimensional materials, which could enable tunable superconductivity that benefits the quantum science applications.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Rapid Solidification Effects in Additively Manufactured Si and SiGe Compositions
SiGe alloys have a proven track record as robust high-temperature thermoelectric materials, powering NASA missions like SNAP-10A, LES-9, and Voyager 1 and 2. Enhancing thermoelectric efficiency hinges on minimizing thermal conductivity while preserving electrical conductivity. Rapid solidification via LPBF can generate microstructural features such as subgrain cellular boundaries and twinning, which may help reduce thermal conductivity while preserving semiconducting behavior. Here, this study investigates the potential of laser powder bed fusion (LPBF) additive manufacturing to fabricate nanostructured Si and SiGe thermoelectric materials. High cooling rates (10 5 to 10 7 K/s) rates inherent to the LPBF process are conducive to forming such nanostructures. Moreover, this fabrication technique could also be suitable for fabricating complex geometries needed to achieve improved device level performance. Process mapping of commercial Si powder with irregular morphology was first performed to understand the LPBF processing behavior of this semiconductor material. Subsequent studies included in-house synthesized B-doped (p-type) Si7 8 Ge 22 spherical powder that was produced via ultrasonic atomization. Scan strategies involved multiple laser exposures to mitigate solidification cracking: a high density of >98% was achieved, but solidification cracking could not be fully eliminated. Subsequently, a high electrical resistivity (i.e., low conductivity) was observed, but the measured Seebeck coefficient, ∼230 μV/K @ 500 °C, proved that good semiconductor material was being fabricated. A subgrain cellular structure (5–10 μm) was observed as defined by Ge segregation to the intercellular boundaries. The remelting strategies helped lower the cooling rates in processing SiGe, but this still resulted in high residual stresses, which induced a remarkably high density of twins (78–95%) to accommodate the deformation. This unique grain structure offers an avenue for phonon scattering and potential improvements in thermoelectric performance.
figure of merit↗
Plasmonic Enhancement of the Photoluminescence in Hybrid Structures with SiGe Quantum Dots and Ag Nanoislands
Plasmonic enhancement of the photoluminescence in hybrid structures with SiGe quantum dots and Ag nanoislands was found. Ag nanoislands grown on the top of the multilayer structures with SiGe quantum dots (QDs) support a surface plasmon resonance that can be tuned to the QD emission wavelength by changing of Ag nanoparticle parameters. Photoluminescence measurements of the hybrid metal-semiconductor nanostructures revealed a fourfold increase of the integral intensity of SiGe QD emission in the spectral range from 0.8 to 1 eV.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Plastic recovery and self-healing in longitudinally twinned SiGe nanowires
This paper reports on plastic recovery and self-healing behavior in longitudinally-twinned and [112] orientated SiGe nanowire (NW) beams when they are subjected to large bending strains. The NW alloys are comprised of lamellar nanotwin platelet(s) sandwiched between two semi-cylindrical twins. The loading curves, which are acquired from atomic force microscope (AFM) based three-point bending tests, reveal the onset of plastic deformation at a characteristic stress threshold, followed by further straining of the NWs. This ductility is attributed to dislocation activity within the semi-cylindrical crystal portions of the NW, which are hypothesized to undergo a combination of elastic and plastic straining. On the other hand, the lamellar nanoplatelets undergo purely elastic stretching. During the unloading process, the release of internal elastic stresses enables dislocation backflow and escape at the surface. As a result, the dislocations are predominantly annihilated and the NW samples evidenced self-healing via plastic recovery even at ultra-large strains, which are estimated using finite-element models at 16.3% in one of the tested devices. Finite element analysis also establishes the independence of the observed nanomechanical behavior on the relative orientation of the load with respect to the nanoplatelet. This first observation of reversible plasticity in the SiGe material system, which is aided by a concurrent evolution of segmented elastic and plastic deformation within its grains during the loading process, presents an important new pathway for mechanical stabilization of technologically important group-IV semiconductor nanomaterials.
36 MATERIALS SCIENCE↗
Formation of tubular conduction channel in a SiGe(P)/Si core/shell nanowire heterostructure
Realizing a tubular conduction channel within a one-dimensional core–shell nanowire (NW) enables better understanding of quantum phenomena and exploration of electronic device applications. Herein, we report the growth of a SiGe(P)/Si core/shell NW heterostructure using a chemical vapor deposition coupled with vapor–liquid–solid growth mechanism. The entire NW heterostructure behaves as a p-type semiconductor, which demonstrates that the high-density carriers are confined within the 4 nm-thick Si shell and form a tubular conduction channel. These findings are confirmed by both calculations and the gate-dependent current–voltage ( I d – V g ) characteristics. Atomic resolution microscopic analyses suggest a coherent epitaxial core/shell interface where strain is released by forming dislocations along the axial direction of the NW heterostructure. Additional surface passivation achieved via growing a SiGe(P)/Si/SiGe core/multishell NW heterostructure suggests potential strategies to enhance the tubular carrier density, which could be further modified by improving multishell crystallinity and structural design.
36 MATERIALS SCIENCE↗
Materials Data on SiGe by Materials Project
SiGe is Zincblende, Sphalerite structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Ge4+ is bonded to four equivalent Si4- atoms to form corner-sharing GeSi4 tetrahedra. All Ge–Si bond lengths are 2.42 Å. Si4- is bonded to four equivalent Ge4+ atoms to form corner-sharing SiGe4 tetrahedra.
36 MATERIALS SCIENCE↗
Materials Data on SiGe by Materials Project
SiGe crystallizes in the monoclinic P2_1 space group. The structure is three-dimensional. there are eight inequivalent Ge4+ sites. In the first Ge4+ site, Ge4+ is bonded in a single-bond geometry to one Si4- atom. The Ge–Si bond length is 2.41 Å. In the second Ge4+ site, Ge4+ is bonded in a trigonal non-coplanar geometry to three Si4- atoms. All Ge–Si bond lengths are 2.42 Å. In the third Ge4+ site, Ge4+ is bonded in a single-bond geometry to one Si4- atom. The Ge–Si bond length is 2.42 Å. In the fourth Ge4+ site, Ge4+ is bonded in a trigonal non-coplanar geometry to three Si4- atoms. There are a spread of Ge–Si bond distances ranging from 2.42–2.44 Å. In the fifth Ge4+ site, Ge4+ is bonded in a single-bond geometry to one Si4- atom. The Ge–Si bond length is 2.43 Å. In the sixth Ge4+ site, Ge4+ is bonded in a trigonal non-coplanar geometry to three Si4- atoms. There are one shorter (2.42 Å) and two longer (2.43 Å) Ge–Si bond lengths. In the seventh Ge4+ site, Ge4+ is bonded in a trigonal non-coplanar geometry to three Si4- atoms. There are a spread of Ge–Si bond distances ranging from 2.42–2.44 Å. In the eighth Ge4+ site, Ge4+ is bonded in a single-bond geometry to one Si4- atom. The Ge–Si bond length is 2.41 Å. There are eight inequivalent Si4- sites. In the first Si4- site, Si4- is bonded to one Ge4+ and three Si4- atoms to form corner-sharing SiSi3Ge tetrahedra. There are one shorter (2.38 Å) and two longer (2.39 Å) Si–Si bond lengths. In the second Si4- site, Si4- is bonded to three Ge4+ and one Si4- atom to form corner-sharing SiSiGe3 tetrahedra. The Si–Si bond length is 2.38 Å. In the third Si4- site, Si4- is bonded to one Ge4+ and three Si4- atoms to form corner-sharing SiSi3Ge tetrahedra. There are one shorter (2.37 Å) and two longer (2.38 Å) Si–Si bond lengths. In the fourth Si4- site, Si4- is bonded to three Ge4+ and one Si4- atom to form corner-sharing SiSiGe3 tetrahedra. The Si–Si bond length is 2.36 Å. In the fifth Si4- site, Si4- is bonded to one Ge4+ and three Si4- atoms to form corner-sharing SiSi3Ge tetrahedra. In the sixth Si4- site, Si4- is bonded to three Ge4+ and one Si4- atom to form corner-sharing SiSiGe3 tetrahedra. In the seventh Si4- site, Si4- is bonded to three Ge4+ and one Si4- atom to form corner-sharing SiSiGe3 tetrahedra. In the eighth Si4- site, Si4- is bonded to one Ge4+ and three Si4- atoms to form corner-sharing SiSi3Ge tetrahedra.
36 MATERIALS SCIENCE↗
Controlled Formation of Stacked Si Quantum Dots in Vertical SiGe Nanowires
In this work, we demonstrate the ability to fabricate vertically stacked Si quantum dots (QDs) within SiGe nanowires with QD diameters down to 2 nm. These QDs are formed during high-temperature dry oxidation of Si/SiGe heterostructure pillars, during which Ge diffuses along the pillars’ sidewalls and encapsulates the Si layers. Continued oxidation results in QDs with sizes dependent on oxidation time. The formation of a Ge-rich shell that encapsulates the Si QDs is observed, a configuration which is confirmed to be thermodynamically favorable with molecular dynamics and density functional theory. The type-II band alignment of the Si dot/SiGe pillar suggests that charge trapping on the Si QDs is possible, and electron energy loss spectra show that a conduction band offset of at least 200 meV is maintained for even the smallest Si QDs. Our approach is compatible with current Si-based manufacturing processes, offering a new avenue for realizing Si QD devices.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Humble planar defects in SiGe nanopillars
We report a {001} planar defect found in SiGe nanopillars. The defect structure, determined by atomic-resolution electron microscopy, matches the Humble defect model proposed for diamond. We also investigate several possible variants of the Humble structure using first-principles calculations and find that the one lowest in energy is in agreement with the scanning transmission electron microscope images. The pillar composition has been analyzed with electron energy loss spectroscopy, which hints at how the defect is formed. Our results show that the structure and formation process of defects in nanostructured group IV semiconductors can be different from their bulk counterparts.
36 MATERIALS SCIENCE↗
Atomic-layer doping of SiGe heterostructures for atomic-precision donor devices
As a first step to porting scanning tunneling microscopy methods of atomic-precision fabrication to a strained-Si/SiGe platform, we demonstrate post-growth P atomic-layer doping of SiGe heterostructures. To preserve the substrate structure and elastic state, we use a T ≤ 800 °C process to prepare clean Si 0.86 Ge 0.14 surfaces suitable for atomic-precision fabrication. P-saturated atomic-layer doping is incorporated and capped with epitaxial Si under a thermal budget compatible with atomic-precision fabrication. Hall measurements at T = 0.3 K show that the doped heterostructure has R $\square$ = 570 ± 30 Ω , yielding an electron density n e = 2.1 ± 0.1 × 10 14 cm -2 and mobility μ e = 52 ± 3 cm 2 V -1 s -1 , similar to saturated atomic-layer doping in pure Si and Ge. The magnitude of μ e and the complete absence of Shubnikov–de Haas oscillations in magnetotransport measurements indicate that electrons are overwhelmingly localized in the donor layer, and not within a nearby buried Si well. Finally, this conclusion is supported by self-consistent Schrödinger-Poisson calculations that predict electron occupation primarily in the donor layer.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Quantification of Dopant Profiles in SiGe HBT Devices
We report on the use of atom probe tomography (APT), scanning transmission electron microscopy (STEM), and secondary ion mass spectroscopy (SIMS) to characterize doping profiles in the base region of SiGe HBT devices. We compare SIMS profiles obtained from large regions (400 um 2 ) of the device wafer to profiles obtained from individual devices of different emitter window widths (0.25 and 0.18 um 2 ) using APT. From this comparison we show how APT can provide a deeper insight into evaluating the fabrication process and its effects on electrical models of device performance and enabling the building of higher performance systems. We also demonstrate that APT can be used to characterize defects within the intrinsic regions of a device.
Jones, Eric↗
Materials Data on V10(SiGe)3 by Materials Project
V10(GeSi)3 crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. there are three inequivalent V sites. In the first V site, V is bonded in a 8-coordinate geometry to two equivalent V, three equivalent Ge, and three equivalent Si atoms. There are one shorter (2.40 Å) and one longer (2.50 Å) V–V bond lengths. All V–Ge bond lengths are 2.54 Å. All V–Si bond lengths are 2.52 Å. In the second V site, V is bonded in a 5-coordinate geometry to three equivalent Ge and two equivalent Si atoms. There are two shorter (2.48 Å) and one longer (2.58 Å) V–Ge bond lengths. Both V–Si bond lengths are 2.65 Å. In the third V site, V is bonded in a 5-coordinate geometry to two equivalent Ge and three equivalent Si atoms. Both V–Ge bond lengths are 2.67 Å. There are two shorter (2.46 Å) and one longer (2.62 Å) V–Si bond lengths. Ge is bonded in a 9-coordinate geometry to nine V atoms. Si is bonded in a 9-coordinate geometry to nine V atoms.
36 MATERIALS SCIENCE↗
Materials Data on Mn10(SiGe)3 by Materials Project
Mn10(GeSi)3 crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. there are three inequivalent Mn sites. In the first Mn site, Mn is bonded in a 5-coordinate geometry to three equivalent Ge and two equivalent Si atoms. There are two shorter (2.44 Å) and one longer (2.51 Å) Mn–Ge bond lengths. Both Mn–Si bond lengths are 2.66 Å. In the second Mn site, Mn is bonded in a 5-coordinate geometry to two equivalent Ge and three equivalent Si atoms. Both Mn–Ge bond lengths are 2.67 Å. There are two shorter (2.42 Å) and one longer (2.54 Å) Mn–Si bond lengths. In the third Mn site, Mn is bonded in a 6-coordinate geometry to three equivalent Ge and three equivalent Si atoms. All Mn–Ge bond lengths are 2.48 Å. All Mn–Si bond lengths are 2.46 Å. Ge is bonded in a 9-coordinate geometry to nine Mn atoms. Si is bonded in a 9-coordinate geometry to nine Mn atoms.
36 MATERIALS SCIENCE↗
Materials Data on Y10(SiGe)3 by Materials Project
Y10(GeSi)3 crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. there are three inequivalent Y sites. In the first Y site, Y is bonded in a 6-coordinate geometry to three equivalent Ge and three equivalent Si atoms. All Y–Ge bond lengths are 3.08 Å. All Y–Si bond lengths are 3.06 Å. In the second Y site, Y is bonded in a 3-coordinate geometry to three equivalent Ge and two equivalent Si atoms. There are two shorter (2.93 Å) and one longer (3.08 Å) Y–Ge bond lengths. Both Y–Si bond lengths are 3.45 Å. In the third Y site, Y is bonded in a 5-coordinate geometry to two equivalent Ge and three equivalent Si atoms. Both Y–Ge bond lengths are 3.45 Å. There are two shorter (2.93 Å) and one longer (3.09 Å) Y–Si bond lengths. Ge is bonded in a 9-coordinate geometry to nine Y atoms. Si is bonded in a 9-coordinate geometry to nine Y atoms.
36 MATERIALS SCIENCE↗