We describe an alternative strategy to the fabrication of Ge–Sn based materials on Si by using chlorogermane (GeH 3 Cl) instead of the specialty Ge hydrides (Ge 2 H 6 , Ge 3 H 8 , Ge 4 H 10 ) currently employed as ultra-low temperature sources of Ge. This simpler and potentially more practical chlorinated derivative is obtained in high yields and in research-grade purity by direct reactions of commercial GeH 4 and SnCl 4 and exhibits favorable physical and chemical properties that make it an effective source of Ge for a wide range of chemical vapor deposition (CVD) processing conditions. As a proof-of concept, we have employed GeH 3 Cl to demonstrate deposition of pure Ge and GeSn hetero-structures on large-area Si wafers, at conditions compatible with current specialty methods for next generation technologies but with higher deposition efficiency, ensuring an optimal use of the Ge feedstock. In the case of pure Ge, GeH 3 Cl has enabled growth of thick and uniform Ge layers with flat surfaces and relaxed microstructures at 330–360 °C, exhibiting lower residual doping than obtained by alternate Ge hydride methods. GeH 3 Cl allows for in situ doping with the same facility as the Ge hydrides, and this has enabled the design and fabrication of homo-structure pin photodetectors exhibiting low dark current densities and closer to ideal optical collection efficiencies when compared to devices produced by other Ge-on-Si approaches. In the case of GeSn, the high reactivity of GeH 3 Cl toward Sn hydrides has enabled the formation of mono-crystalline alloy layers at ultra-low temperatures between 200–300 °C and conditions akin to molecular beam epitaxy (MBE). Combined, these results suggest an intriguing potential for this new CVD process in the device-application space. The deployment of GeH 3 Cl as a highly reactive low-temperature Ge-source could not only improve on the current wasteful methods that use GeH 4 , but also eliminate the need for the higher-cost polygermanes.
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Dehydrocoupling – an alternative approach to functionalizing germanium nanoparticle surfaces
Surface functionalization is an essential aspect of nanoparticle design and preparation; it can impart stability, processability, functionality, as well as tailor optoelectronic properties that facilitate future applications. Herein we report a new approach toward modifying germanium nanoparticle (GeNP) surfaces and for the first time tether alkyl chains to the NP surfaces through Si–Ge bonds. This was achieved via heteronuclear dehydrocoupling reactions involving alkylsilanes and Ge–H moieties on the NP surfaces. The resulting solution processable RR′ 2 Si–GeNPs (R = octadecyl or PDMS; R′ = H or CH 3 ) were characterized using FTIR, Raman, 1 H-NMR, XRD, TEM, HAADF, and EELS and were found to retain the crystallinity of the parent GeNP platform.
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- Award ID(s):
- 2018427
- NSF-PAR ID:
- 10292813
- Date Published:
- Journal Name:
- Nanoscale
- Volume:
- 12
- Issue:
- 11
- ISSN:
- 2040-3364
- Page Range / eLocation ID:
- 6271 to 6278
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The nature of halogen bonding under different dielectric conditions remains underexplored, especially for inorganic systems. The structural and energetic properties of model halogen bonded complexes (R3M−I—NH3for R=H and F, and M=C, Si, and Ge) are examined computationally for relative permittivities between 1 and 109 using an implicit solvent model. We confirm and assess the exceptionally high maximum potentials at the sigma hole on I (
V s,max ) in F3Ge−I relative to cases where M=C or Si. In particular, Ge far outperforms Si in mediating inductive effects. Linear relationships, typically with R2>0.97, are identified betweenV s,max , the full point charge on I in R3M−I, and the interaction energy, and optimized I—N distance in the complexes. An anomalous trend is identified in which, for each M, F3M−I—NH3becomesless stable as the optimized I—N distance getsshorter in different dielectric environments; it is explained using the F−I—NH3complex as a reference. -
We report the synthesis of Ge1−ySny films containing 6%–13% Sn directly on Si(100) for monolithic integration applications, circumventing the use of conventional Ge-buffer layers. The films are produced in a gas source molecular epitaxy chamber at ultralow temperatures of 185–210 °C and a pressure of 10−5 Torr by the reactions of pure vapor Ge4H10 and SnD4 or SnH4 without carrier gases. Very small amounts of Si, incorporated via the Si4H10 precursor, can be used to improve the structural properties. All samples were characterized by XRD, RBS, IR-ellipsometry, AFM, and TEM, indicating the formation of monocrystalline single-phase films with relatively low defectivity and flat surfaces. A notable highlight is that the residual strains of the alloy layers are much lower compared to those grown on Ge buffers and can be further reduced by rapid thermal annealing without decomposition, indicating that growth on bare silicon should produce bulklike, high Sn content alloys that cannot be accessed using Ge buffers. N-type analogs of the above samples doped with phosphorus were also produced using P(SiH3)3 as the in situ dopant precursor. The results collectively illustrate the potential of our chemistry-based method to generate good quality Ge1−ySny layers directly on large area Si wafers bypassing Ge buffers that typically lead to complications such as multiple hetero-interfaces and epitaxial breakdown at high Sn concentrations.more » « less
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Abstract The chemical dynamics of the elementary reaction of ground state atomic silicon (Si;3P) with germane (GeH4; X1A1) were unraveled in the gas phase under single collision condition at a collision energy of 11.8±0.3 kJ mol−1exploiting the crossed molecular beams technique contemplated with electronic structure calculations. The reaction follows indirect scattering dynamics and is initiated through an initial barrierless insertion of the silicon atom into one of the four chemically equivalent germanium‐hydrogen bonds forming a triplet collision complex (HSiGeH3;
3 i1 ). This intermediate underwent facile intersystem crossing (ISC) to the singlet surface (HSiGeH3;1 i1 ). The latter isomerized via at least three hydrogen atom migrations involving exotic, hydrogen bridged reaction intermediates eventually leading to the H3SiGeH isomeri5 . This intermediate could undergo unimolecular decomposition yielding the dibridged butterfly‐structured isomer1 p1 (Si(μ‐H2)Ge) plus molecular hydrogen through a tight exit transition state. Alternatively, up to two subsequent hydrogen shifts toi6 andi7 , followed by fragmentation of each of these intermediates, could also form1 p1 (Si(μ‐H2)Ge) along with molecular hydrogen. The overall non‐adiabatic reaction dynamics provide evidence on the existence of exotic dinuclear hydrides of main group XIV elements, whose carbon analog structures do not exist. -
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Abstract We have explored the structural and energetic properties of a series of RMX3‐NH3(M=Si, Ge; X=F, Cl; R=CH3, C6H5) complexes using density functional theory and low‐temperature infrared spectroscopy. In the minimum‐energy structures, the NH3binds axially to the metal, opposite a halogen, while the organic group resides in an equatorial site. Remarkably, the primary mode of interaction in several of these systems seems to be hydrogen bonding (C‐H‐‐N) rather than a tetrel (N→M) interaction. This is particularly clear for the RMCl3‐NH3complexes, and analyses of the charge distributions of the acid fragment corroborate this assessment. We also identified a set of metastable geometries in which the ammonia binds opposite the organic substituent in an axial orientation. Acid fragment charge analyses also provide a clear rationale as to why these configurations are less stable than the minimum‐energy structures. Matrix‐isolation infrared spectra provide clear evidence for the occurrence of the minimum‐energy form of CH3SiCl3–NH3, but analogous results for CH3GeCl3–NH3are less conclusive. Computational scans of the M‐N distance potentials for CH3SiCl3–NH3and CH3GeCl3–NH3, both in the gas phase and bulk dielectric media, reveal a great deal of anharmonicity and a propensity for condensed‐phase structural change.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/c9nr10837h
