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Igura K, Nozawa K, Ishiyama T, Suemasu T, Toko K. Strain-dependent grain boundary properties of n-type germanium layers. Sci Rep 2024; 14:7812. [PMID: 38565560 PMCID: PMC10987518 DOI: 10.1038/s41598-024-56282-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2023] [Accepted: 03/04/2024] [Indexed: 04/04/2024] Open
Abstract
Polycrystalline Ge thin films have attracted considerable attention as potential materials for use in various electronic and optical devices. We recently developed a low-temperature solid-phase crystallization technology for a doped Ge layer and achieved the highest electron mobility in a polycrystalline Ge thin film. In this study, we investigated the effects of strain on the crystalline and electrical properties of n-type polycrystalline Ge layers. By inserting a GeOx interlayer directly under Ge and selecting substrates with different coefficients of thermal expansion, we modulated the strain in the polycrystalline Ge layer, ranging from approximately 0.6% (tensile) to - 0.8% (compressive). Compressive strain enlarged the grain size to 12 µm, but decreased the electron mobility. The temperature dependence of the electron mobility clarified that changes in the potential barrier height of the grain boundary caused this behavior. Furthermore, we revealed that the behavior of the grain boundary barrier height with respect to strain is opposite for the n- and p-types. This result strongly suggests that this phenomenon is due to the piezoelectric effect. These discoveries will provide guidelines for improving the performance of Ge devices and useful physical knowledge of various polycrystalline semiconductor thin films.
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Affiliation(s)
- Kota Igura
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8573, Japan
| | - Koki Nozawa
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8573, Japan.
| | - Takamitsu Ishiyama
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8573, Japan
- JSPS Research Fellow, 8 Ichiban-cho, Chiyoda-ku, Tokyo, 102-8472, Japan
| | - Takashi Suemasu
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8573, Japan
| | - Kaoru Toko
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8573, Japan.
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2
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Maeda S, Ishiyama T, Nishida T, Ozawa T, Saitoh N, Yoshizawa N, Suemasu T, Toko K. High Thermoelectric Performance in Polycrystalline GeSiSn Ternary Alloy Thin Films. ACS APPLIED MATERIALS & INTERFACES 2022; 14:54848-54854. [PMID: 36450141 DOI: 10.1021/acsami.2c14785] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Group IV materials are promising candidates for highly reliable and human-friendly thin-film thermoelectric generators, used for micro-energy harvesting. In this study, we investigated the synthesis and thermoelectric applications of a Ge-based ternary alloy thin film, Ge1-x-ySixSny. The solid-phase crystallization of the highly densified amorphous precursors allowed the formation of high-quality polycrystalline Ge1-x-ySixSny layers on an insulating substrate. The small compositions of Si and Sn in Ge1-x-ySixSny (x < 0.15 and y < 0.05) lowered the thermal conductivity (3.1 W m-1 K-1) owing to the alloy scattering of phonons, while maintaining a high carrier mobility (approximately 200 cm2 V-1 s-1). The solid-phase diffusion of Ga and P allowed us to control the carrier concentration to the order of 1019 cm-3 for holes and 1018 cm-3 for electrons. For both p- and n-type Ge1-x-ySixSny, the power factor peaked at x = 0.06 and y = 0.02, reaching 1160 μW m-1 K-2 for p-type and 2040 μW m-1 K-2 for n-type. The resulting dimensionless figure of merits (0.12 for p-type and 0.20 for n-type) are higher than those of most environmentally friendly thermoelectric thin films. These results indicate that group IV alloys are promising candidates for high-performance, reliable thin-film thermoelectric generators.
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Affiliation(s)
- Shintaro Maeda
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki305-8573, Japan
| | - Takamitsu Ishiyama
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki305-8573, Japan
| | - Takeshi Nishida
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki305-8573, Japan
| | - Tomoki Ozawa
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki305-8573, Japan
| | - Noriyuki Saitoh
- Electron Microscope Facility, TIA, AIST, 1-2-1 Namiki, Tsukuba, Ibaraki305-8564, Japan
| | - Noriko Yoshizawa
- Global Zero Emission Research Center, AIST, 16-1 Onogawa, Tsukuba, Ibaraki305-8569, Japan
| | - Takashi Suemasu
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki305-8573, Japan
| | - Kaoru Toko
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki305-8573, Japan
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3
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Imajo T, Ishiyama T, Nozawa K, Suemasu T, Toko K. Acceptor defects in polycrystalline Ge layers evaluated using linear regression analysis. Sci Rep 2022; 12:14941. [PMID: 36056074 PMCID: PMC9440008 DOI: 10.1038/s41598-022-19221-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2022] [Accepted: 08/25/2022] [Indexed: 11/09/2022] Open
Abstract
Polycrystalline Ge thin films have recently attracted renewed attention as a material for various electronic and optical devices. However, the difficulty in the Fermi level control of polycrystalline Ge films owing to their high density of defect-induced acceptors has limited their application in the aforementioned devices. Here, we experimentally estimated the origin of acceptor defects by significantly modulating the crystallinity and electrical properties of polycrystalline Ge layers and investigating their correlation. Our proposed linear regression analysis method, which is based on deriving the acceptor levels and their densities from the temperature dependence of the hole concentration, revealed the presence of two different acceptor levels. A systematic analysis of the effects of grain size and post annealing on the hole concentration suggests that deep acceptor levels (53-103 meV) could be attributed to dangling bonds located at grain boundaries, whereas shallow acceptor levels (< 15 meV) could be attributed to vacancies in grains. Thus, this study proposed a machine learning-based simulation method that can be widely applied in the analysis of physical properties, and can provide insights into the understanding and control of acceptor defects in polycrystalline Ge thin films.
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Affiliation(s)
- Toshifumi Imajo
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8573, Japan.,JSPS Research Fellow, 8 Ichiban-cho, Chiyoda-ku, Tokyo, 102-8472, Japan
| | - Takamitsu Ishiyama
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8573, Japan
| | - Koki Nozawa
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8573, Japan
| | - Takashi Suemasu
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8573, Japan
| | - Kaoru Toko
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8573, Japan.
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4
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Yamashita Y, Takayanagi K, Gotoh K, Toko K, Usami N, Suemasu T. Zn 1-xGe xO y Passivating Interlayers for BaSi 2 Thin-Film Solar Cells. ACS APPLIED MATERIALS & INTERFACES 2022; 14:13828-13835. [PMID: 35170952 DOI: 10.1021/acsami.1c23070] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
BaSi2 is a promising absorber material for next-generation thin-film solar cells (TFSCs). For high-efficiency TFSCs, a suitable interlayer should be found for every light absorber. However, such an interlayer has not been studied for BaSi2. In this study, we investigated amorphous Zn1-xGexOy films as interlayers for BaSi2. The Zn/Ge atomic ratio in the Zn1-xGexOy film and the optical band gap depend on the substrate temperature during sputtering deposition. A suitable i-Zn1-xGexOy/BaSi2 heterointerface with spike-type conduction band offset was achieved when Zn1-xGexOy was deposited on BaSi2 at 50 °C. Furthermore, photoresponsivity measurements revealed that Zn1-xGexOy has an excellent surface passivation effect on BaSi2. When the thickness of Zn1-xGexOy was 2 nm, a high photoresponsivity of 0.9 A/W was obtained for a 500 nm thick BaSi2 layer at a wavelength of 780 nm under an applied bias voltage of 0.5 V between the front and rear electrodes, where the photoresponsivity in the short-wavelength region was significantly improved compared with that of BaSi2 capped with an amorphous Si layer. X-ray photoelectron spectroscopy revealed that the Zn1-xGexOy films suppressed the oxidation of the BaSi2 surface, decreasing the carrier recombination rate. This is the first demonstration of passivation interlayers for BaSi2 with suitable band alignment for carrier transport and surface passivation effects.
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Affiliation(s)
- Yudai Yamashita
- Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan
| | - Kaori Takayanagi
- Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan
| | - Kazuhiro Gotoh
- Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
| | - Kaoru Toko
- Department of Applied Physics, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan
| | - Noritaka Usami
- Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
| | - Takashi Suemasu
- Department of Applied Physics, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan
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Ozawa T, Murata M, Suemasu T, Toko K. Flexible Thermoelectric Generator Based on Polycrystalline SiGe Thin Films. MATERIALS 2022; 15:ma15020608. [PMID: 35057324 PMCID: PMC8782019 DOI: 10.3390/ma15020608] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 12/25/2021] [Accepted: 01/12/2022] [Indexed: 12/07/2022]
Abstract
Flexible and reliable thermoelectric generators (TEGs) will be essential for future energy harvesting sensors. In this study, we synthesized p- and n-type SiGe layers on a high heat-resistant polyimide film using metal-induced layer exchange (LE) and demonstrated TEG operation. Despite the low process temperature (<500 °C), the polycrystalline SiGe layers showed high power factors of 560 µW m−1 K−2 for p-type Si0.4Ge0.6 and 390 µW m−1 K−2 for n-type Si0.85Ge0.15, owing to self-organized doping in LE. Furthermore, the power factors indicated stable behavior with changing measurement temperature, an advantage of SiGe as an inorganic material. An in-plane π-type TEG based on these SiGe layers showed an output power of 0.45 µW cm−2 at near room temperature for a 30 K temperature gradient. This achievement will enable the development of environmentally friendly and highly reliable flexible TEGs for operating micro-energy devices in the future Internet of Things.
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Affiliation(s)
- Tomoki Ozawa
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8573, Japan; (T.O.); (T.S.)
| | - Masayuki Murata
- Research Institute for Energy Conservation, AIST, Tsukuba 305-8569, Japan
- Correspondence: (M.M.); (K.T.)
| | - Takashi Suemasu
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8573, Japan; (T.O.); (T.S.)
| | - Kaoru Toko
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8573, Japan; (T.O.); (T.S.)
- Correspondence: (M.M.); (K.T.)
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6
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Toko K, Murata H. Layer exchange synthesis of multilayer graphene. NANOTECHNOLOGY 2021; 32:472005. [PMID: 34384058 DOI: 10.1088/1361-6528/ac1d05] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2021] [Accepted: 08/11/2021] [Indexed: 06/13/2023]
Abstract
Low-temperature synthesis of multilayer graphene (MLG) on arbitrary substrates is the key to incorporating MLG-based functional thin films, including transparent electrodes, low-resistance wiring, heat spreaders, and battery anodes in advanced electronic devices. This paper reviews the synthesis of MLG via the layer exchange (LE) phenomenon between carbon and metal from its mechanism to the possibility of device applications. The mechanism of LE is completely different from that of conventional MLG precipitation methods using metals, and the resulting MLG exhibits unique features. Modulation of metal species and growth conditions enables synthesis of high-quality MLG over a wide range of growth temperatures (350 °C-1000 °C) and MLG thicknesses (5-500 nm). Device applications are discussed based on the high electrical conductivity (2700 S cm-1) of MLG and anode operation in Li-ion batteries. Finally, we discuss the future challenges of LE for MLG and its application to flexible devices.
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Affiliation(s)
- Kaoru Toko
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, Japan
| | - Hiromasa Murata
- Device Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
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7
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Grain size dependent photoresponsivity in GaAs films formed on glass with Ge seed layers. Sci Rep 2021; 11:10159. [PMID: 33980891 PMCID: PMC8115577 DOI: 10.1038/s41598-021-89342-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2021] [Accepted: 04/22/2021] [Indexed: 11/21/2022] Open
Abstract
The strong correlation between grain size and photoresponsivity in polycrystalline GaAs films on glass was experimentally demonstrated using Ge seed layers with a wide range of grain sizes (1‒330 μm). The crystal evaluations using Raman spectroscopy, scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy revealed that 500-nm-thick GaAs films epitaxially grown from the Ge seed layers at 550 °C inherited the grain boundaries and crystal orientations in Ge. With increasing grain size, the photoresponsivity corresponding to GaAs increased from 0.01 to 3 A W−1 under a bias voltage of 0.3 V. The maximum value approached that of the GaAs film formed simultaneously on a single-crystal Ge wafer, indicating the high potential of the large-grained GaAs film. Knowledge gained from this study will be essential for designing advanced solar cells based on polycrystalline III–V compound semiconductors using inexpensive substrates.
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8
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Imajo T, Suemasu T, Toko K. Strain effects on polycrystalline germanium thin films. Sci Rep 2021; 11:8333. [PMID: 33859279 PMCID: PMC8050231 DOI: 10.1038/s41598-021-87616-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Accepted: 03/24/2021] [Indexed: 11/11/2022] Open
Abstract
Polycrystalline Ge thin films have attracted increasing attention because their hole mobilities exceed those of single-crystal Si wafers, while the process temperature is low. In this study, we investigate the strain effects on the crystal and electrical properties of polycrystalline Ge layers formed by solid-phase crystallization at 375 °C by modulating the substrate material. The strain of the Ge layers is in the range of approximately 0.5% (tensile) to -0.5% (compressive), which reflects both thermal expansion difference between Ge and substrate and phase transition of Ge from amorphous to crystalline. For both tensile and compressive strains, a large strain provides large crystal grains with sizes of approximately 10 μm owing to growth promotion. The potential barrier height of the grain boundary strongly depends on the strain and its direction. It is increased by tensile strain and decreased by compressive strain. These findings will be useful for the design of Ge-based thin-film devices on various materials for Internet-of-things technologies.
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Affiliation(s)
- Toshifumi Imajo
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8573, Japan. .,JSPS Research Fellow, 8 Ichiban-cho, Chiyoda-ku, Tokyo, 102-8472, Japan.
| | - Takashi Suemasu
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8573, Japan
| | - Kaoru Toko
- Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8573, Japan. .,PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama, 332-0012, Japan.
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9
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Weißhaupt D, Funk HS, Kern M, Dettling MM, Schwarz D, Oehme M, Sürgers C, van Slageren J, Fischer IA, Schulze J. Weak localization and weak antilocalization in doped Ge 1-y Sn y layers with up to 8% Sn. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:085703. [PMID: 33290269 DOI: 10.1088/1361-648x/abcb68] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Low-temperature magnetoresistance measurements of n- and p-doped germanium-tin (Ge1-y Sn y ) layers with Sn concentrations up to 8% show contributions arising from effects of weak localization for n-type and weak antilocalization for p-type doped samples independent of the Sn concentration. Calculations of the magnetoresistance using the Hikami-Larkin-Nagaoka model for two-dimensional transport allow us to extract the phase-coherence length for all samples as well as the spin-orbit length for the p-type doped samples. For pure Ge, we find phase-coherence lengths as long as (349.0 ± 1.4) nm and (614.0 ± 0.9) nm for n-type and p-type doped samples, respectively. The phase-coherence length decreases with increasing Sn concentration. From the spin-orbit scattering length, we determine the spin-diffusion scattering length in the range of 20-30 nm for all highly degenerate p-type doped samples irrespective of Sn concentration. These results show that Ge1-y Sn y is a promising material for future spintronic applications.
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Affiliation(s)
- David Weißhaupt
- Institute of Semiconductor Engineering (IHT), University of Stuttgart, Stuttgart, Germany
| | - Hannes S Funk
- Institute of Semiconductor Engineering (IHT), University of Stuttgart, Stuttgart, Germany
| | - Michal Kern
- Institute of Physical Chemistry (IPC), University of Stuttgart, Stuttgart, Germany
| | - Marco M Dettling
- Institute of Semiconductor Engineering (IHT), University of Stuttgart, Stuttgart, Germany
| | - Daniel Schwarz
- Institute of Semiconductor Engineering (IHT), University of Stuttgart, Stuttgart, Germany
| | - Michael Oehme
- Institute of Semiconductor Engineering (IHT), University of Stuttgart, Stuttgart, Germany
| | - Christoph Sürgers
- Physikalisches Institut (PHI), Karlsruhe Institute of Technology, Karlsruhe, Germany
| | - Joris van Slageren
- Institute of Physical Chemistry (IPC), University of Stuttgart, Stuttgart, Germany
| | - Inga A Fischer
- Experimental Physics and Functional Materials, Brandenburg University of Technology (BTU), Cottbus, Germany
| | - Jörg Schulze
- Institute of Semiconductor Engineering (IHT), University of Stuttgart, Stuttgart, Germany
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10
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Shklyaev AA, Latyshev AV. Dewetting behavior of Ge layers on SiO 2 under annealing. Sci Rep 2020; 10:13759. [PMID: 32792554 PMCID: PMC7426840 DOI: 10.1038/s41598-020-70723-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2020] [Accepted: 07/27/2020] [Indexed: 11/09/2022] Open
Abstract
The solid-state dewetting phenomenon in Ge layers on SiO2 is investigated as a function of layer thickness dGe (from 10 to 86 nm) and annealing temperature. The dewetting is initiated at about 580-700 °C, depending on dGe, through the appearance of surface undulation leading to the particle formation and the rupture of Ge layers by narrow channels or rounded holes in the layers with the thicknesses of 10-60 and 86 nm, respectively. The channel widths are significantly narrower than the distance between the particles that causes the formation of thinned Ge layer areas between particles at the middle dewetting stage. The thinned areas are then agglomerated into particles of smaller sizes, leading to the bimodal distributions of the Ge particles which are different in shape and size. The existence of a maximum in the particle pair correlation functions, along with the quadratic dependence of the corresponding particle spacing on dGe, may indicate the spinodal mechanism of the dewetting in the case of relatively thin Ge layers. Despite the fact that the particle shape, during the solid-state dewetting, is not thermodynamically equilibrium, the use of the Young's equation and contact angles allows us to estimate the particle/substrate interface energy.
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Affiliation(s)
- A A Shklyaev
- A.V. Rzhanov Institute of Semiconductor Physics, SB RAS, Novosibirsk, 630090, Russia.
| | - A V Latyshev
- A.V. Rzhanov Institute of Semiconductor Physics, SB RAS, Novosibirsk, 630090, Russia
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Maity G, Ojha S, Dubey S, Kulriya PK, Sulania I, Dhar S, Som T, Kanjilal D, Patel SP. Crystallization of Ge in ion-irradiated amorphous-Ge/Au thin films. CrystEngComm 2020. [DOI: 10.1039/c9ce01584a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Herein, the structural, optical, and electrical properties of Au-induced crystallization in amorphous germanium (a-Ge) thin films are presented for future solar energy material applications.
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Affiliation(s)
- G. Maity
- Department of Pure and Applied Physics
- Guru Ghasidas Vishwavidyalaya (A Central University)
- Bilaspur 495009
- India
| | - S. Ojha
- Inter University Accelerator Centre
- New Delhi 110067
- India
| | - S. Dubey
- Department of Physics
- School of Engineering
- University of Petroleum and Energy Studies
- Dehradun-248007
- India
| | - P. K. Kulriya
- Inter University Accelerator Centre
- New Delhi 110067
- India
| | - I. Sulania
- Inter University Accelerator Centre
- New Delhi 110067
- India
| | - S. Dhar
- Department of Physics
- Shiv Nadar University
- Nagar-201314
- India
| | - T. Som
- Institute of Physics
- Bhubaneswar-751005
- India
| | - D. Kanjilal
- Inter University Accelerator Centre
- New Delhi 110067
- India
| | - Shiv P. Patel
- Department of Pure and Applied Physics
- Guru Ghasidas Vishwavidyalaya (A Central University)
- Bilaspur 495009
- India
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12
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High-electron-mobility (370 cm 2/Vs) polycrystalline Ge on an insulator formed by As-doped solid-phase crystallization. Sci Rep 2019; 9:16558. [PMID: 31719607 PMCID: PMC6851082 DOI: 10.1038/s41598-019-53084-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2019] [Accepted: 10/21/2019] [Indexed: 11/08/2022] Open
Abstract
High-electron-mobility polycrystalline Ge (poly-Ge) thin films are difficult to form because of their poor crystallinity, defect-induced acceptors and low solid solubility of n-type dopants. Here, we found that As doping into amorphous Ge significantly influenced the subsequent solid-phase crystallization. Although excessive As doping degraded the crystallinity of the poly-Ge, the appropriate amount of As (~1020 cm−3) promoted lateral growth and increased the Ge grain size to approximately 20 μm at a growth temperature of 375 °C. Moreover, neutral As atoms in poly-Ge reduced the trap-state density and energy barrier height of the grain boundaries. These properties reduced grain boundary scattering and allowed for an electron mobility of 370 cm2/Vs at an electron concentration of 5 × 1018 cm−3 after post annealing at 500 °C. The electron mobility further exceeds that of any other n-type poly-Ge layers and even that of single-crystal Si wafers with n ≥ 1018 cm−3. The low-temperature synthesis of high-mobility Ge on insulators will provide a pathway for the monolithic integration of high-performance Ge-CMOS onto Si-LSIs and flat-panel displays.
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13
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Improving carrier mobility of polycrystalline Ge by Sn doping. Sci Rep 2018; 8:14832. [PMID: 30287869 PMCID: PMC6172198 DOI: 10.1038/s41598-018-33161-z] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Accepted: 09/24/2018] [Indexed: 11/23/2022] Open
Abstract
To improve the performance of electronic devices, extensive research efforts have recently focused on the effect of incorporating Sn into Ge. In the present work, we investigate how Sn composition x (0 ≤ x ≤ 0.12) and deposition temperature Td (50 ≤ Td ≤ 200 °C) of the Ge1−xSnx precursor affect subsequent solid-phase crystallization. Upon incorporating 3.2% Sn, which is slightly above the solubility limit of Sn in Ge, the crystal grain size increases and the grain-boundary barrier decreases, which increases the hole mobility from 80 to 250 cm2/V s. Furthermore, at Td = 125 °C, the hole mobility reaches 380 cm2/V s, which is tentatively attributed to the formation of a dense amorphous GeSn precursor. This is the highest hole mobility for semiconductor thin films on insulators formed below 500 °C. These results thus demonstrate the usefulness of Sn doping of polycrystalline Ge and the importance of temperature while incorporating Sn. These findings make it possible to fabricate advanced Ge-based devices including high-speed thin-film transistors.
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High Temperature High Sensitivity Multipoint Sensing System Based on Three Cascade Mach⁻Zehnder Interferometers. SENSORS 2018; 18:s18082688. [PMID: 30115819 PMCID: PMC6111578 DOI: 10.3390/s18082688] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/29/2018] [Accepted: 08/08/2018] [Indexed: 02/04/2023]
Abstract
A temperature multipoint sensing system based on three cascade Mach⁻Zehnder interferometers (MZIs) is introduced. The MZIs with different lengths are fabricated based on waist-enlarged fiber bitapers. The fast Fourier transformation is applied to the overlapping transmission spectrum and the corresponding interference spectra can be obtained via the cascaded frequency spectrum based on the inverse Fourier transformation. By analyzing the drift of interference spectra, the temperature response sensitivities of 0.063 nm/°C, 0.071 nm/°C, and 0.059 nm/°C in different furnaces can be detected from room temperature up to 1000 °C, and the temperature response at different regions can be measured through the sensitivity matrix equation. These results demonstrate feasibility of multipoint measurement, which also support that the temperature sensing system provides new solution to the MZI cascade problem.
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