Clathrates of Tetrel elements (Si, Ge, Sn) have attracted interest for their potential use in batteries and other applications. Sodium-filled silicon clathrates are conventionally synthesized through thermal decomposition of the Zintl precursor Na4Si4, but phase selectivity of the product is often difficult to achieve. Herein, we report the selective formation of the type I clathrate Na8Si46using electrochemical oxidation at 450 °C and 550 °C. A two-electrode cell design inspired by high-temperature sodium-sulfur batteries is employed, using Na4Si4as working electrode, Na
Synthesis of short-wave infrared Ge1− y Sn y semiconductors directly on Si(100) via ultralow temperature molecular routes for monolithic integration applications
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.
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- Award ID(s):
- 2119583
- NSF-PAR ID:
- 10447841
- Date Published:
- Journal Name:
- Journal of Vacuum Science & Technology A
- Volume:
- 40
- Issue:
- 6
- ISSN:
- 0734-2101
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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β″ -alumina solid electrolyte, and counter electrode consisting of molten Na or Sn. Galvanostatic intermittent titration is implemented to observe the oxidation characteristics and reveals a relatively constant cell potential under quasi-equilibrium conditions, indicating a two-phase reaction between Na4Si4and Na8Si46. We further demonstrate that the product selection and morphology can be altered by tuning the reaction temperature and Na vapor pressure. Room temperature lithiation of the synthesized Na8Si46is evaluated for the first time, showing similar electrochemical characteristics to those in the type II clathrate Na24Si136. The results show that solid-state electrochemical oxidation of Zintl phases at high temperatures can lead to opportunities for more controlled crystal growth and a deeper understanding of the formation processes of intermetallic clathrates. -
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.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1116/6.0002052
