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1. Room-Temperature Intrinsic and Extrinsic Damping in Polycrystalline Fe Thin Films

Author

Wu, Shuang, Smith, David A., Nakarmi, Prabandha, Rai, Anish, Clavel, Michael, Hudait, Mantu K., Zhao, Jing, Michel, F. Marc, Mewes, Claudia, Mewes, Tim, and Emori, Satoru

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We examine room-temperature magnetic relaxation in polycrystalline Fe films. Out-of-plane ferromagnetic resonance (FMR) measurements reveal Gilbert damping parameters of $\approx$ 0.0024 for Fe films with thicknesses of 4-25 nm, regardless of their microstructural properties. The remarkable invariance with film microstructure strongly suggests that intrinsic Gilbert damping in polycrystalline metals at room temperature is a local property of nanoscale crystal grains, with limited impact from grain boundaries and film roughness. By contrast, the in-plane FMR linewidths of the Fe films exhibit distinct nonlinear frequency dependences, indicating the presence of strong extrinsic damping. To fit our in-plane FMR data, we have used a grain-to-grain two-magnon scattering model with two types of correlation functions aimed at describing the spatial distribution of inhomogeneities in the film. However, neither of the two correlation functions is able to reproduce the experimental data quantitatively with physically reasonable parameters. Our findings advance the fundamental understanding of intrinsic Gilbert damping in structurally disordered films, while demonstrating the need for a deeper examination of how microstructural disorder governs extrinsic damping.

Published
2021
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2. Magnetic Damping in Epitaxial Fe Alloyed with Vanadium and Aluminum

Author

Smith, David A., Rai, Anish, Lim, Youngmin, Hartnett, Timothy, Sapkota, Arjun, Srivastava, Abhishek, Mewes, Claudia, Jiang, Zijian, Clavel, Michael, Hudait, Mantu K., Viehland, Dwight D., Heremans, Jean J., Balachandran, Prasanna V., Mewes, Tim, and Emori, Satoru

Subjects
Condensed Matter - Materials Science
Abstract

To develop low-moment, low-damping metallic ferromagnets for power-efficient spintronic devices, it is crucial to understand how magnetic relaxation is impacted by the addition of nonmagnetic elements. Here, we compare magnetic relaxation in epitaxial Fe films alloyed with light nonmagnetic elements of V and Al. FeV alloys exhibit lower intrinsic damping compared to pure Fe, reduced by nearly a factor of 2, whereas damping in FeAl alloys increases with Al content. Our experimental and computational results indicate that reducing the density of states at the Fermi level, rather than the average atomic number, has a more significant impact in lowering damping in Fe alloyed with light elements. Moreover, FeV is confirmed to exhibit an intrinsic Gilbert damping parameter of $\simeq$0.001, among the lowest ever reported for ferromagnetic metals., Comment: 28 pages, 9 figures

Published
2020
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7. Electronic and optical properties of highly boron-doped epitaxial Ge/AlAs(001) heterostructures.

Author

Clavel, Michael B., Liu, Jheng-Sin, Meeker, Michael A., Khodaparast, Giti A., Xie, Yuantao, Heremans, Jean J., Bhattacharya, Shuvodip, and Hudait, Mantu K.

Subjects
*OPTICAL properties, *MOLECULAR beam epitaxy, *SPIN-orbit interactions, *EPITAXIAL layers, *VALENCE bands, *BORON
Abstract

The impact of elemental boron (B) doping on the structural, optical, and magnetotransport properties of epitaxial Ge/AlAs/GaAs(001) heterostructures, grown by solid-source molecular beam epitaxy, was comprehensively investigated. Cross-sectional transmission electron microscopy analysis revealed atomically abrupt Ge:B/AlAs and AlAs/GaAs heterointerfaces and a lack of observable long-range defect formation or B segregation in the epitaxial Ge:B layer. Spectral broadening observed in the measured temperature-dependent photoluminescence spectra suggested valence band mixing during recombination, implying a splitting of the valence band heavy- and light-hole degeneracy due to residual strain resulting from substitutional B incorporation in the Ge epilayer. Temperature-dependent magnetotransport analysis of the B-doped Ge thin films exhibited the tell-tale signature of antilocalization, indicating observable spin–orbit interaction in the Ge:B system. Moreover, the temperature- and magnetic field-dependent magnetotransport results indicate the presence of single-carrier, p-type conduction in the Ge:B film, further affirming the successful incorporation and activation of B at a high concentration (∼4 × 1019 cm−3) and elimination of parallel conduction via the large-bandgap AlAs buffer. Together, these results provide insights into the effects of heavy doping (via elemental solid-source doping) on Ge-based heterostructures and their feasibility in future electronic and photonic applications. [ABSTRACT FROM AUTHOR]

Published
2020
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14. Kilovolt Tri-Gate GaN Junction HEMTs with High Thermal Stability

Author

Ma, Yunwei, primary, Xiao, Ming, additional, Zhang, Yuhao, additional, Du, Zhonghao, additional, Yan, Xiaodong, additional, Wang, Han, additional, Cheng, Kai, additional, Clavel, Michael, additional, Hudait, Mantu K., additional, Tao, Lei, additional, Lin, Feng, additional, and Kravchenko, Ivan, additional

Published
2021
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16. Tri-gate GaN junction HEMT

Author

Ma, Yunwei, primary, Xiao, Ming, additional, Du, Zhonghao, additional, Yan, Xiaodong, additional, Cheng, Kai, additional, Clavel, Michael, additional, Hudait, Mantu K., additional, Kravchenko, Ivan, additional, Wang, Han, additional, and Zhang, Yuhao, additional

Published
2020
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18. Magnetic Damping in Epitaxial Iron Alloyed with Vanadium and Aluminum

Author

Smith, David A., primary, Rai, Anish, additional, Lim, Youngmin, additional, Hartnett, Timothy Q., additional, Sapkota, Arjun, additional, Srivastava, Abhishek, additional, Mewes, Claudia, additional, Jiang, Zijian, additional, Clavel, Michael, additional, Hudait, Mantu K., additional, Viehland, Dwight D., additional, Heremans, Jean J., additional, Balachandran, Prasanna V., additional, Mewes, Tim, additional, and Emori, Satoru, additional

Published
2020
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20. TBAL: Tunnel FET-Based Adiabatic Logic for Energy-Efficient, Ultra-Low Voltage IoT Applications

Author

Liu, Jheng-Sin, Clavel, Michael B., Hudait, Mantu K., and Electrical and Computer Engineering

Subjects
FinFETs, strained Ge/InGaAs heterojunctions, Hardware_INTEGRATEDCIRCUITS, Adiabatic logic, tunnel field-effect transistors, Hardware_PERFORMANCEANDRELIABILITY, TBAL, Hardware_LOGICDESIGN
Abstract

A novel, tunnel field-effect transistor (TFET)-based adiabatic logic (TBAL) circuit topology has been proposed, evaluated and benchmarked with several device architectures (planar MOSFET, FinFET, and TFET) and AL implementations (efficient charge recovery logic, 2N-2N2P, positive feedback adiabatic logic) operating in the ultra-low voltage (0.3 V ≥ VDD ≤ 0.6 V) regime. By incorporating adiabatic logic functionality into standard combinational logic, an 80% reduction in energy/cycle was achieved. A further 80% reduction in energy/cycle was demonstrated by utilizing near broken-gap TFET devices and simultaneous scaling of supply voltage to 0.3 V, resulting in a 96% reduction in energy/cycle as compared to conventional Si CMOS. Extension of operating frequency beyond 10 MHz, coupled with sub-threshold circuit operation, shows the feasibility of TBAL for energy-efficient Internet of Things applications.

Published
2019

21. Growth and characterization of metamorphic InAs/GaSb tunnel heterojunction on GaAs by molecular beam epitaxy.

Author

Jheng-Sin Liu, Clavel, Michael B., Pandey, Rahul, Datta, Suman, Meeker, Michael, Khodaparast, Giti A., and Hudait, Mantu K.

Subjects
*TUNNEL diodes, *MOLECULAR beam epitaxy, *X-rays, *PHOTOLUMINESCENCE, *TRANSISTORS
Abstract

The structural, morphological, optical, and electrical transport characteristics of a metamorphic, broken-gap InAs/GaSb p-i-n tunnel diode structure, grown by molecular beam epitaxy on GaAs, were demonstrated. Precise shutter sequences were implemented for the strain-balanced InAs/GaSb active layer growth on GaAs, as corroborated by high-resolution X-ray analysis. Cross-sectional transmission electron microscopy and detailed micrograph analysis demonstrated strain relaxation primarily via the formation of 90° Lomer misfit dislocations (MDs) exhibiting a 5.6 nm spacing and intermittent 60° MDs at the GaSb/GaAs heterointerface, which was further supported by a minimal lattice tilt of 180 arc sec observed during X-ray analysis. Selective area diffraction and Fast Fourier Transform patterns confirmed the full relaxation of the GaSb buffer layer and quasi-ideal, strain-balanced InAs/GaSb heteroepitaxy. Temperature-dependent photoluminescence measurements demonstrated the optical band gap of the GaSb layer. Strong optical signal at room temperature from this structure supports a high-quality material synthesis. Current–voltage characteristics of fabricated InAs/GaSb p-i-n tunnel diodes measured at 77K and 290K demonstrated two bias-dependent transport mechanisms. The Shockley–Read–Hall generation-recombination mechanism at low bias and band-to-band tunneling transport at high bias confirmed the p-i-n tunnel diode operation. This elucidated the importance of defect control in metamorphic InAs/GaSb tunnel diodes for the implementation of low-voltage and high-performance tunnel field effect transistor applications. [ABSTRACT FROM AUTHOR]

Published
2016
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22. AIP Advances

Author

Hudait, Mantu K., Clavel, Michael B., Saluru, Sarat K., Liu, Jheng-Sin, Meeker, Michael A., Khodaparast, Giti A., Bodnar, Robert J., and Electrical and Computer Engineering

Abstract

The impact of bulk and surface defect states on the vibrational and optical properties of step-graded epitaxial GaAs₁₋ySby (0 ≤ y ≤ 1) materials with and without chemical surface treatment by (NH₄)₂S was investigated. Tunable antimony (Sb) composition GaAs₁₋ySby epitaxial layers, grown by solid source molecular beam epitaxy (MBE), were realized on GaAs and Si substrates by varying key growth parameters (e.g., Sb/Ga flux ratio, growth temperature). Raman and photoluminescence (PL) spectroscopic analysis of (NH₄)₂S-treated GaAs₁₋ySby epitaxial layers revealed composition-independent Raman spectral widths and enhanced PL intensity (1.3x) following (NH₄)₂S surface treatment, indicating bulk defect-minimal epitaxy and a reduction in the surface recombination velocity corresponding to reduced surface defect sites, respectively. Moreover, quantification of the luminescence recombination mechanisms across a range of measurement temperatures and excitation intensities (i.e., varying laser power) indicate the presence of free-electron to neutral acceptor pair or Sb-defect-related recombination pathways, with detectable bulk defect recombination discernible only in binary GaSb PL spectra. In addition, PL analysis of the short- and long-term thermodynamic stability of sulfur-treated GaAs₁₋ySby/Al₂O₃ heterointerfaces revealed an absence of quantifiable atomic interdiffusion or native oxide formation. Leveraging the combined Raman and PL analysis herein, the quality of the heteroepitaxial step-graded epitaxial GaAs₁₋ySby materials can be optimized for optical devices.

Published
2018

23. Tensile-Strained Ge/III-V Heterostructures for Low-Power Nanoelectronic Devices

Author

Clavel, Michael Brian

Subjects
Nanoelectronics, Microelectronics, Semiconductor Devices, Semiconductor Materials, Tunnel Field-Effect Transistors, Molecular Beam Epitaxy, Germanium, Compound Semiconductors
Abstract

The aggressive reduction of feature size in silicon (Si)-based complimentary metal-oxide-semiconductor (CMOS) technology has resulted in an exponential increase in computing power. Stemming from increases in device density and substantial progress in materials science and transistor design, the integrated circuit has seen continual performance improvements and simultaneous reductions in operating power (VDD). Nevertheless, existing Si-based metal-oxide-semiconductor field-effect transistors (MOSFETs) are rapidly approaching the physical limits of their scaling potential. New material innovations, such as binary group IV or ternary III-V compound semiconductors, and novel device architectures, such as the tunnel field-effect transistor (TFET), are projected to continue transistor miniaturization beyond the Si CMOS era. Unlike conventional MOSFET technology, TFETs operate on the band-to-band tunneling injection of carriers from source to channel, thereby resulting in steep switching characteristics. Furthermore, narrow bandgap semiconductors, such as germanium (Ge) and InxGa1-xAs, enhance the ON-state current and improve the switching behavior of TFET devices, thus making these materials attractive candidates for further study. Moreover, epitaxial growth of Ge on InxGa1-xAs results in tensile stress (ε) within the Ge thin-film, thereby giving device engineers the ability to tune its material properties (e.g., mobility, bandgap) via strain engineering and in so doing enhance device performance. For these reasons, this research systematically investigates the material, optical, electronic transport, and heterointerfacial properties of ε-Ge/InxGa1-xAs heterostructures grown on GaAs and Si substrates. Additionally, the influence of strain on MOS interfaces with Ge is examined, with specific application toward low-defect density ε-Ge MOS device design. Finally, vertical ε-Ge/InxGa1-xAs tunneling junctions are fabricated and characterized for the first time, demonstrating their viability for the continued development of next-generation low-power nanoelectronic devices utilizing the Ge/InxGa1-xAs material system.

Published
2024

30. Tensile-Strained Ge/InₓGa₁₋ₓAs Heterostructures for Electronic and Photonic Applications

Author

Clavel, Michael Brian, Electrical and Computer Engineering, Hudait, Mantu K., Heremans, Jean J., and Orlowski, Marius K.

Subjects
Tunnel Field-Effect Transistor, Silicon, Photonics, InGaAs, Tensile Strain, Germanium, Molecular Beam Epitaxy, Heterogeneous Integration
Abstract

The continued scaling of feature size in silicon (Si)-based complimentary metal-oxide-semiconductor (CMOS) technology has led to a rapid increase in compute power. Resulting from increases in device densities and advances in materials and transistor design, integrated circuit (IC) performance has continued to improve while operational power (VDD) has been substantially reduced. However, as feature sizes approach the atomic length scale, fundamental limitations in switching characteristics (such as subthreshold slope, SS, and OFF-state power dissipation) pose key technical challenges moving forward. Novel material innovations and device architectures, such as group IV and III-V materials and tunnel field-effect transistors (TFETs), have been proposed as solutions for the beyond Si era. TFETs benefit from steep switching characteristics due to the band-to-band tunneling injection of carriers from source to channel. Moreover, the narrow bandgaps of III-V and germanium (Ge) make them attractive material choices for TFETs in order to improve ON-state current and reduce SS. Further, Ge grown on InₓGa₁₋ₓAs experiences epitaxy-induced strain (ε), further reducing the Ge bandgap and improving carrier mobility. Due to these reasons, the ε-Ge/InₓGa₁₋ₓAs system is a promising candidate for future TFET architectures. In addition, the ability to tune the bandgap of Ge via strain engineering makes ε-Ge/InₓGa₁₋ₓAs heterostructures attractive for nanoscale group IV-based photonics, thereby benefitting the monolithic integration of electronics and photonics on Si. This research systematically investigates the material, optical, and heterointerface properties of ε-Ge/InₓGa₁₋ₓAs heterostructures on GaAs and Si substrates. The effect of strain on the heterointerface band alignment is comprehensively studied, demonstrating the ability to modulate the effective tunneling barrier height (Ebeff) and thus the threshold voltage (VT), ON-state current, and SS in future ε-Ge/InₓGa₁₋ₓAs TFETs. Further, band structure engineering via strain modulation is shown to be an effective technique for tuning the emission properties of Ge. Moreover, the ability to heterogeneously integrate these structures on Si is demonstrated for the first time, indicating their viability for the development of next-generation high performance, low-power logic and photonic integrated circuits on Si. Master of Science

Published
2015

31. Device Characterization of a Sulfur-Implanted p<inline-formula><tex-math notation="LaTeX">$^{++}$</tex-math></inline-formula>/p GaSb Photovoltaic Camel Diode

Author

Herrera, Daniel J., Clavel, Michael B., Hudait, Mantu K., and Lester, Luke F.

Abstract

The implantation and rapid thermal annealing of sulfur (S+) ions has previously been shown to be an effective method in non-epitaxially attaining hole carrier concentrations as high as $1\times {10^{19}} \; \rm cm^{-3}$ in gallium antimonide (GaSb). This technique was used to fabricate a photovoltaic diode by delta-doping the front surface of a p-type GaSb substrate and forming a p++/p junction. The steep potential created using this process is increased by strong Fermi level pinning at the metal/p++ interface, resulting in a camel diode with a barrier height of 0.51 eV. A post-fabrication etch process succeeded in improving the short circuit current density to 41.8 mA/cm$^2$ and the internal quantum efficiency to 90% by enhancing the carrier lifetime away from the front metal contact grid. Likewise, the open circuit voltage improved to 0.21 V, with an intrinsic fill factor above 40%. These results offer the potential of a significantly higher power output than similar non-epitaxial devices made on n-type GaSb substrates.

Published
2020
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36. Structural and optical properties of sulfur passivated epitaxial step-graded GaAs1-ySby materials.

Author

Hudait, Mantu K., Clavel, Michael B., Saluru, Sarat, Liu, Jheng-Sin, Meeker, Michael A., Khodaparast, Giti A., and Bodnar, Robert J.

Subjects
*EPITAXY, *PASSIVATION, *OPTICAL properties
Abstract

The impact of bulk and surface defect states on the vibrational and optical properties of step-graded epitaxial GaAs1-ySby (0 ≤ y ≤ 1) materials with and without chemical surface treatment by (NH4)2S was investigated. Tunable antimony (Sb) composition GaAs1-ySby epitaxial layers, grown by solid source molecular beam epitaxy (MBE), were realized on GaAs and Si substrates by varying key growth parameters (e.g., Sb/Ga flux ratio, growth temperature). Raman and photoluminescence (PL) spectroscopic analysis of (NH4)2S-treated GaAs1-ySby epitaxial layers revealed composition-independent Raman spectral widths and enhanced PL intensity (1.3×) following (NH4)2S surface treatment, indicating bulk defect-minimal epitaxy and a reduction in the surface recombination velocity corresponding to reduced surface defect sites, respectively. Moreover, quantification of the luminescence recombination mechanisms across a range of measurement temperatures and excitation intensities (i.e., varying laser power) indicate the presence of free-electron to neutral acceptor pair or Sb-defect-related recombination pathways, with detectable bulk defect recombination discernible only in binary GaSb PL spectra. In addition, PL analysis of the short- and long-term thermodynamic stability of sulfur-treated GaAs1-ySby/Al2O3 heterointerfaces revealed an absence of quantifiable atomic interdiffusion or native oxide formation. Leveraging the combined Raman and PL analysis herein, the quality of the heteroepitaxial step-graded epitaxial GaAs1-ySby materials can be optimized for optical devices. [ABSTRACT FROM AUTHOR]

Published
2018
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46. Lead-free epitaxial ferroelectric material integration on semiconducting (100) Nb-doped SrTiO3 for low-power non-volatile memory and efficient ultraviolet ray detection

Author

Kundu, Souvik, primary, Clavel, Michael, additional, Biswas, Pranab, additional, Chen, Bo, additional, Song, Hyun-Cheol, additional, Kumar, Prashant, additional, Halder, Nripendra N., additional, Hudait, Mantu K., additional, Banerji, Pallab, additional, Sanghadasa, Mohan, additional, and Priya, Shashank, additional

Published
2015
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