[Show abstract][Hide abstract] ABSTRACT: In this letter, we study the formation and electrical properties of Ni-GaSb alloys by direct reaction of Ni with GaSb. It is found that several properties of Ni-antimonide alloys, including low thermal budget processing (300°C), low Schottky barrier height for holes (~0.1 eV), low sheet resistance of Ni-InGaSb (53 Ω/square), and low specific contact resistivity (7.6×10)-7Ω cm2), show good progress toward antimonide-based metal source/drain (S/D) p-channel metal-oxide-semiconductor field-effect transistors. Devices with a self-aligned metal S/D were demonstrated, in which heterostructure design is adopted to further improve the performance, e.g., ON/OFF ratio , subthreshold swing (140 mV/decade), and high effective-field hole mobility of ~510 cm2/Vs at sheet charge density of 2×1012 cm-2.
IEEE Electron Device Letters 11/2013; 34(11):1367-1369. · 3.02 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this work, the effect of Ge point defect healing process between 550 °C and 650 °C is investigated, in the aspect of leakage (off) current and junction depth of Ge n+/p junction diodes using ECV, TEM, J-V, and SIMS analyses. After 600 °C anneal, off-current density (2 × 10−4 A/cm2) is dramatically reduced due to the defect healing phenomenon that decreases the number of point defects, subsequently providing a higher on/off-current ratio of 5 × 103. In spite of the high healing temperature, junction diodes seem not to suffer from the deep diffusion of phosphorus (P) in Ge because those diffuse mostly through VGe. In addition, it is also confirmed that Ti is an appropriate material in terms of diffusion barrier and diffusivity for Ge n+/p junction contact metal.
Journal of Applied Physics 09/2013; 114(9):094515-6. · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper, a theoretical analysis of unstrained GeSn alloys as a laser gain medium was performed. Using the empirical pseudopotential method, the band structure of GeSn alloys was simulated and verified against experimental data. This model shows that GeSn becomes direct bandgap with 6.55% Sn concentration. The optical gain of GeSn alloys with 0-10% Sn concentration was calculated with different n-type doping concentrations and injection levels. It is shown theoretically that adding Sn greatly increases the differential gain owing to the reduction of energy between the direct and indirect conduction bands. For a double-heterostructure laser, the model shows that at a cavity loss of 50 cm-1, the minimum threshold current density drops 60 times from Ge to Ge0.9Sn0.1, and the corresponding optimum n-doping concentration of the active layer drops by almost two orders of magnitude. These results indicate that GeSn alloys are good candidates for a Si-compatible laser.
IEEE Journal of Selected Topics in Quantum Electronics 09/2013; 19(5):1502706-1502706. · 3.47 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Process conditions of gallium phosphide (GaP) metal-organic chemical vapor deposition growth on silicon (Si) are optimized by material characterization. Thorough investigation of GaP-Si interface at this optimized growth condition is carried out by electrical characterization with the perspective of applying this heterostructure system for improving the performance of logic transistors and retention time of capacitorless single-transistor dynamic RAM (1T-DRAM). Fabricated GaP-Si heterojunction diodes exhibit an ON-OFF ratio of 108 with similar reverse current as the ideal device simulation results signify immunity to the existing antiphase domains. Finally, MOSFET devices with GaP source-drain having subthreshold swing of 70 mV/dec and an ON-OFF ratio of 105 are demonstrated.
IEEE Transactions on Electron Devices 07/2013; 60(7):2238-2245. · 2.36 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Semiconductor heterostructures play a vital role in photonics and electronics. They are typically realized by growing layers of different materials, complicating fabrication and limiting the number of unique heterojunctions on a wafer. In this article, we present single-material nanowires which behave exactly like traditional heterostructures. These pseudo-heterostructures have electronic band profiles that are custom-designed at the nanoscale by strain engineering. Since the band profile depends only on the nanowire geometry with this approach, arbitrary band profiles can be individually tailored at the nanoscale using existing nanolithography. We report the first experimental observations of spatially-confined, greatly enhanced (>200x), and wavelength-shifted (>500 nm) emission from strain-induced potential wells that facilitate effective carrier collection at room temperature. This work represents a fundamentally new paradigm for creating nanoscale devices with full heterostructure behavior in photonics and electronics.
[Show abstract][Hide abstract] ABSTRACT: The effect of uniaxial-strain, band-structure, mobility, effective masses, density of states, channel orientation and high-field transport on the drive current, off-state leakage and switching delay in nano-scale, Silicon (Si) and Germanium (Ge), p-MOS DGFETs is thoroughly and systematically investigated. To accurately model and capture all these complex effects, different simulation techniques, such as the Non-local Empirical Pseudopotential method (bandstructure), Full-Band Monte-Carlo Simulations (transport), 1-D Poisson-Schrodinger (electrostatics) and detailed Band-To-Band-Tunneling (BTBT) (including bandstructure and quantum effects) simulations, were used in this study.
[Show abstract][Hide abstract] ABSTRACT: Using the Non-local Empirical Pseudopotential method (bandstructure), Full-Band Monte-Carlo Simulations (transport), 1-D Poisson-Schrodinger (electrostatics) and detailed Band-To-Band-Tunneling (BTBT) (including bandstructure and quantum effects) simulations, the effect of uniaxial-and biaxial-strain, band-structure, mobility, effective masses, density of states, channel orientation and high-field transport on the drive current, off-state leakage and switching delay in nano-scale, Si, SiGe and Ge, p-MOS DGFETs is thoroughly and systematically investigated.
[Show abstract][Hide abstract] ABSTRACT: Low density-of-states (DOS) of carriers and higher dielectric constants in III-Vs warrants transistor architecture with better electrostatics than conventional bulk FinFETs . Additionally, the integration of III-V FinFETs on 300mm silicon wafers is a key technological challenge due to the large lattice-mismatch between III-Vs and silicon . This paper presents a statistical variability study of III-V and Si FinFETs, from which SOI-FinFET architecture is recommended for III-Vs. The co-integration of InAs-OI NMOS and GaSb-OI PMOS on silicon is proposed for its excellent carrier transport and favorable band-lineup. Such hetero-integration is demonstrated on silicon substrate using rapid-melt-growth technique.
[Show abstract][Hide abstract] ABSTRACT: In this work, we demonstrate the low temperature fabrication of high quality GeSn-On-Insulator (GSOI) which forms the crucial module for monolithic 3DIC. The use of GeSn and Ge overcomes many challenges of monolithic 3D integration, including the need for Si-compatible high-mobility and direct gap materials. Furthermore, we introduce excellent passivation of the semiconductor/buried oxide (BOX) interface which is crucial to the high performance of devices on the stacked layers.
[Show abstract][Hide abstract] ABSTRACT: We propose a vertical gate all around 1-transistor DRAM cell with silicon channel and gallium phosphide source drain (GaP-SD) as a viable alternative to the present 1T-1C DRAM technology. The valence band offset at GaP and Si interface helps to store more holes in the transistor body and thus improves the retention time by 2 order over conventional Si-SD 1T DRAM. By examining body thickness variability, we conclude that GaP-SD memory cell can withstand the performance degradation due to device variability to meet the ITRS retention time requirements. Finally the GaP-SD memory cell is optimized for scaled dimensions upto 20nm body thickness to establish its superiority at lower technology nodes.
Simulation of Semiconductor Processes and Devices (SISPAD), 2013 International Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: We report uniaxial tensile strains up to 5.0% in lithographically patterned germanium nanowires, which is enough strain to make germanium a direct bandgap semiconductor. Theoretically, this strain can reduce a germanium laser's threshold by >16,000x.
Group IV Photonics (GFP), 2013 IEEE 10th International Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: High-Mobility n-MOSFET options with Ge and InGaAs channels are of intense interests. As the well-known interfacial trap (Dit) problem appears now contained, new challenges are emerging from above the interface. The evidence of oxide border traps (BT) in high-k dielectrics and its effect on the on-state performance of Ge and InGaAs n-MOSFETs are presented in this study through combined trap and transport analyses. The impact of the oxide traps on device frequency response and threshold voltage (Vth) stability could challenge the commercial realization of the high mobility channel MOSFET.
[Show abstract][Hide abstract] ABSTRACT: We provide a theoretical analysis of the relative merits of tensile strain and n-type doping as approaches to realizing an efficient low-power germanium laser. Ultimately, tensile strain offers threshold reductions of over 200x, and significant improvements in slope efficiency compared with the recently demonstrated 0.25% strained electrically pumped germanium laser. In contrast, doping offers fundamentally limited benefits, and too much doping is harmful. Moreover, we predict that tensile strain reduces the optimal doping value and that experimentally demonstrated doping has already reached its fundamental limit. We therefore theoretically show large (>; 1%) tensile strain to be the most viable path to a practical germanium-on-silicon laser.
[Show abstract][Hide abstract] ABSTRACT: Recent experiments have demonstrated a reduction of Fermi-level pinning in contacts to n-type Ge by the insertion of a thin tunnel barrier at the interface. The presence of fixed charge in these interface layers can contribute to Schottky-barrier reduction. This work theoretically studies the effect of tunnel-barrier fixed charge on the specific contact resistivity. By simulating various tunnel-barrier materials and fixed-charge densities, we estimate the magnitude of fixed charge required for this mechanism to play an important role in Fermi-level unpinning.
IEEE Electron Device Letters 06/2012; 33(6):761-763. · 3.02 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We demonstrate room-temperature electroluminescence (EL) from light-emitting
diodes (LED) on highly strained germanium (Ge) membranes. An external stressor
technique was employed to introduce a 0.76% bi-axial tensile strain in the
active region of a vertical PN junction. Electrical measurements show an on-off
ratio increase of one order of magnitude in membrane LEDs compared to bulk. The
EL spectrum from the 0.76% strained Ge LED shows a 100nm redshift of the center
wavelength because of the strain-induced direct band gap reduction. Finally,
using tight-binding and FDTD simulations, we discuss the implications for
highly efficient Ge lasers.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate electroluminescence (EL) from light-emitting diodes (LEDs) on highly strained germanium (Ge) membranes. Electrical measurements show an on-off ratio increase of one order of magnitude in membrane LEDs compared to bulk. The EL spectrum from the 0.76% strained Ge LED shows a 100nm redshift of the center wavelength. We also discuss the implications for highly efficient Ge lasers.
[Show abstract][Hide abstract] ABSTRACT: Transistors based on III-V semiconductor materials have been used for a variety of analog and high frequency applications driven by the high electron mobilities in III-V materials. On the other hand, the hole mobility in III-V materials has always lagged compared to group-IV semiconductors such as germanium. In this paper, we explore the use of strain and heterostructure design guided by bandstructure modeling to enhance the hole mobility in III-V materials. Parameters such as strain, valence band offset, effective masses, and splitting between the light and heavy hole bands that are important for optimizing hole transport are measured quantitatively using various experimental techniques. A peak Hall mobility for the holes of 960 cm2/Vs is demonstrated and the high hole mobility is maintained even at high sheet charge.
Journal of Applied Physics 01/2012; 111(10):103706-103706-12. · 2.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Germanium-on-silicon lasers have recently been demonstrated. Our theoretical modeling shows that increasing germanium's strain to 1.1%, which we show is achievable, can reduce the threshold for net gain by over a factor of 20.
Lasers and Electro-Optics (CLEO), 2012 Conference on; 01/2012
[Show abstract][Hide abstract] ABSTRACT: Doping of Ge with Sn atoms by ion implantation and annealing by solid
phase epitaxial re-growth process was investigated as a possible way to
create Ge1-xSnx layers. Ion implantation was carried out at liquid
nitrogen to avoid nano-void formation and three implant doses were
tested: 5×1015, 1×1015 and 5×1014 at/cm2,
respectively. Implant energy was set to 45 keV and implants were carried
out through an 11 nm SiNxOy film to prevent Sn out-diffusion upon
annealing. This was only partially effective. Samples were then annealed
in inert atmosphere either at 350°C varying anneal time or for 100 s
varying temperature from 300 to 500°C. SPER was effective to anneal
damage without Sn diffusion at 350° for samples implanted at medium
and low fluences whereas the 5×1015 at/cm2 samples remained with a
~15 nm amorphous layer even when applying the highest thermal budget.