Browsing by Author "Goley, Patrick S."

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    Design, Theoretical, and Experimental Investigation of Tensile-Strained Germanium Quantum-Well Laser Structure
    Hudait, Mantu K.; Murphy-Armando, Felipe; Saladukha, Dzianis; Clavel, Michael B.; Goley, Patrick S.; Maurya, Deepam; Bhattacharya, Shuvodip; Ochalski, Tomasz J. (American Chemical Society, 2021-10-14)
    Strain and band gap engineered epitaxial germanium (ϵ-Ge) quantum-well (QW) laser structures were investigated on GaAs substrates theoretically and experimentally for the first time. In this design, we exploit the ability of an InGaAs layer to simultaneously provide tensile strain in Ge (0.7-1.96%) and sufficient optical and carrier confinement. The direct band-to-band gain, threshold current density (Jth), and loss mechanisms that dominate in the ϵ-Ge QW laser structure were calculated using first-principles-based 30-band k·p electronic structure theory, at injected carrier concentrations from 3 × 1018 to 9 × 1019 cm-3. The higher strain in the ϵ-Ge QW increases the gain at higher wavelengths; however, a decreasing thickness is required by higher strain due to critical layer thickness for avoiding strain relaxation. In addition, we predict that a Jth of 300 A/cm2 can be reduced to <10 A/cm2 by increasing strain from 0.2% to 1.96% in ϵ-Ge lasing media. The measured room-temperature photoluminescence spectroscopy demonstrated direct band gap optical emission, from the conduction band at the Γ-valley to heavy-hole (0.6609 eV) from 1.6% tensile-strained Ge/In0.24Ga0.76As heterostructure grown by molecular beam epitaxy, is in agreement with the value calculated using 30-band k·p theory. The detailed plan-view transmission electron microscopic (TEM) analysis of 0.7% and 1.2% tensile-strained ϵ-Ge/InGaAs structures exhibited well-controlled dislocations within each ϵ-Ge layer. The measured dislocation density is below 4 × 106 cm-2 for the 1.2% ϵ-Ge layer, which is an upper bound, suggesting the superior ϵ-Ge material quality. Structural analysis of the experimentally realistic 1.95% biaxially strained In0.28Ga0.72As/13 nm ϵ-Ge/In0.28Ga0.72As QW structure demonstrated a strained Ge/In0.28Ga0.72As heterointerface with minimal relaxation using X-ray and cross-sectional TEM analysis. Therefore, our monolithic integration of a strained Ge QW laser structure on GaAs and ultimately the transfer of the process to the Si substrate via an InGa(Al)As/III-V buffer architecture would provide a significant step toward photonic technology based on strained Ge on a Si platform.
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    Germanium Based Field-Effect Transistors: Challenges and Opportunities
    Goley, Patrick S.; Hudait, Mantu K. (MDPI, 2014-03-19)
    The performance of strained silicon (Si) as the channel material for today’s metal-oxide-semiconductor field-effect transistors may be reaching a plateau. New channel materials with high carrier mobility are being investigated as alternatives and have the potential to unlock an era of ultra-low-power and high-speed microelectronic devices. Chief among these new materials is germanium (Ge). This work reviews the two major remaining challenges that Ge based devices must overcome if they are to replace Si as the channel material, namely, heterogeneous integration of Ge on Si substrates, and developing a suitable gate stack. Next, Ge is compared to compound III-V materials in terms of p-channel device performance to review how it became the first choice for PMOS devices. Different Ge device architectures, including surface channel and quantum well configurations, are reviewed. Finally, state-of-the-art Ge device results and future prospects are also discussed.
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    Growth, strain relaxation properties and high-kappa dielectric integration of mixed-anion GaAs1-ySby metamorphic materials
    Zhu, Yizheng; Clavel, M.; Goley, Patrick S.; Hudait, Mantu K. (American Institute of Physics, 2014-10-17)
    Mixed-anion, GaAs1-ySby metamorphic materials with a wide range of antimony (Sb) compositions extending from 15% to 62%, were grown by solid source molecular beam epitaxy (MBE) on GaAs substrates. The impact of different growth parameters on the Sb composition in GaAs1-ySby materials was systemically investigated. The Sb composition was well-controlled by carefully optimizing the As/Ga ratio, the Sb/Ga ratio, and the substrate temperature during the MBE growth process. High-resolution x-ray diffraction demonstrated a quasi-complete strain relaxation within each composition of GaAs1-ySby. Atomic force microscopy exhibited smooth surface morphologies across the wide range of Sb compositions in the GaAs1-ySby structures. Selected high-kappa dielectric materials, Al2O3, HfO2, and Ta2O5 were deposited using atomic layer deposition on the GaAs0.38Sb0.62 material, and their respective band alignment properties were investigated by x-ray photoelectron spectroscopy (XPS). Detailed XPS analysis revealed a valence band offset of > 2 eV for all three dielectric materials on GaAs0.38Sb0.62, indicating the potential of utilizing these dielectrics on GaAs0.38Sb0.62 for p-type metal-oxide-semiconductor (MOS) applications. Moreover, both Al2O3 and HfO2 showed a conduction band offset of > 2 eV on GaAs0.38Sb0.62, suggesting these two dielectrics can also be used for n-type MOS applications. The well-controlled Sb composition in several GaAs1-ySby material systems and the detailed band alignment analysis of multiple high-kappa dielectric materials on a fixed Sb composition, GaAs0.38Sb0.62, provides a pathway to utilize GaAs1-ySby materials in future microelectronic and optoelectronic applications. (C) 2014 AIP Publishing LLC.
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    Heteroepitaxial Ge MOS Devices on Si Using Composite AlAs/GaAs Buffer
    Nguyen, Peter D.; Clavel, Michael B.; Goley, Patrick S.; Liu, Jheng-Sin; Allen, Noah P.; Guido, Louis J.; Hudait, Mantu K. (IEEE, 2015-07-01)
    Structural and electrical characteristics of epitaxial germanium (Ge) heterogeneously integrated on silicon (Si) via a composite, large bandgap AlAs/GaAs buffer are investigated. Electrical characteristics of N-type metal-oxide-semiconductor (MOS) capacitors, fabricated from the aforementioned material stack are then presented. Simulated and experimental X-ray rocking curves show distinct Ge, AlAs, and GaAs epilayer peaks. Moreover, secondary ion mass spectrometry, energy dispersive X-ray spectroscopy (EDS) profile, and EDS line profile suggest limited interdiffusion of the underlying buffer into the Ge layer, which is further indicative of the successful growth of device-quality epitaxial Ge layer. The Ge MOS capacitor devices demonstrated low frequency dispersion of 1.80% per decade, low frequency-dependent flat-band voltage, VFB , shift of 153 mV, efficient Fermi level movement, and limited C-V stretch out. Low interface state density (Dit) from 8.55 × 1011 to 1.09 × 1012 cm-2 eV-1 is indicative of a high-quality oxide/Ge heterointerface, an effective electrical passivation of the Ge surface, and a Ge epitaxy with minimal defects. These superior electrical and material characteristics suggest the feasibility of utilizing large bandgap III-V buffers in the heterointegration of high-mobility channel materials on Si for future high-speed complementary metal-oxide semiconductor logic applications.
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    Heterogeneous Integration of Epitaxial Ge on Si using AlAs/GaAs Buffer Architecture: Suitability for Low-power Fin Field-Effect Transistors
    Hudait, Mantu K.; Clavel, Michael B.; Goley, Patrick S.; Jain, Nikhil; Zhu, Yan (Nature Publishing Group, 2014-11-07)
    Germanium-based materials and device architectures have recently appeared as exciting material systems for future low-power nanoscale transistors and photonic devices. Heterogeneous integration of germanium (Ge)-based materials on silicon (Si) using large bandgap buffer architectures could enable the monolithic integration of electronics and photonics. In this paper, we report on the heterogeneous integration of device-quality epitaxial Ge on Si using composite AlAs/GaAs large bandgap buffer, grown by molecular beam epitaxy that is suitable for fabricating low-power fin field-effect transistors required for continuing transistor miniaturization. The superior structural quality of the integrated Ge on Si using AlAs/GaAs was demonstrated using high-resolution x-ray diffraction analysis. High-resolution transmission electron microscopy confirmed relaxed Ge with high crystalline quality and a sharp Ge/AlAs heterointerface. X-ray photoelectron spectroscopy demonstrated a large valence band offset at the Ge/AlAs interface, as compared to Ge/GaAs heterostructure, which is a prerequisite for superior carrier confinement. The temperature-dependent electrical transport properties of the n-type Ge layer demonstrated a Hall mobility of 370 cm2/Vs at 290 K and 457 cm2/Vs at 90 K, which suggests epitaxial Ge grown on Si using an AlAs/ GaAs buffer architecture would be a promising candidate for next-generation high-performance and energy-efficient fin field-effect transistor applications.