[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: 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: 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: 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: 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: We report a low specific contact resistivity of 5.5 x 10-7 Ωcm2 in nickel germanide (NiGe) contacts on n+ Ge. Data fitting with the contact resistivity model by A.M. Roy et al. (2010) suggests SBH of ~0.44eV for NiGe and ~0.55eV for Al/Ti contacts. We correlate this SBH and specific contact resistivity reduction with the dopant segregation at the NiGe/Ge interface and confirm it by SIMS analysis.
[show abstract][hide abstract] ABSTRACT: This work presents a novel method to introduce a sustainable biaxial tensile strain larger than 1% in a thin Ge membrane using a stressor layer integrated on a Si substrate. Raman spectroscopy confirms 1.13% strain and photoluminescence shows a direct band gap reduction of 100meV with enhanced light emission efficiency. Simulation results predict that a combination of 1.1% strain and heavy n(+) doping reduces the required injected carrier density for population inversion by over a factor of 60. We also present the first highly strained Ge photodetector, showing an excellent responsivity well beyond 1.6um.
[show abstract][hide abstract] ABSTRACT: A transfer matrix method for simulating spin injection into semiconductors in the case of high electric fields has been developed. The nonlinear relationship between electron spin density and electrochemical potential splitting, the effect of electric field on spin diffusion lengths, and spin polarized drift current are accounted for. Using this approach, high magnetoresistance (MR) at high electric fields is predicted. This is due to spin accumulation reaching its extreme values for fermion statistics. This effect opens up a new direction for solving the problem of low MR that semiconductor spintronic devices are facing.
IEEE Transactions on Magnetics 11/2011; · 1.42 Impact Factor
[show abstract][hide abstract] ABSTRACT: While there have been many demonstrations on n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) in III-V semiconductors showing excellent electron mobility and high drive currents, hole mobility in III-V p-channel MOSFETs (pMOSFETs) has traditionally lagged in comparison to silicon. GaSb is an attractive candidate for high-performance III-V pMOSFETs due to its high bulk hole mobility. We fabricate and study GaSb pMOSFETs with an atomic layer deposition Al<sub>2</sub>O<sub>3</sub> gate dielectric and a self-aligned source/drain formed by ion implantation. The band offsets of Al<sub>2</sub>O<sub>3</sub> on GaSb were measured using synchrotron radiation photoemission spectroscopy. The use of a forming gas anneal to passivate the dangling bonds in the bulk of the dielectric was demonstrated. The density of interface states D <sub>it</sub> was measured across the GaSb band gap using conductance measurements, and a midband-gap D <sub>it</sub> of 3 × 10<sup>11</sup>/cm<sup>2</sup> eV was achieved. This enabled pMOSFETs with a peak hole mobility value of 290 cm<sup>2</sup>/Vs.
IEEE Transactions on Electron Devices 11/2011; · 2.06 Impact Factor
[show abstract][hide abstract] ABSTRACT: A unified analytical expression is developed to accurately describe the complex band structures in commonly used diamond and zinc-blende semiconductors. Fitting the model to the numerical complex band structures shows a significantly improved accuracy as compared with the effective mass approximation. The model is used to study the band-to-band tunneling in Si, Ge, GaAs and GaSb, with a maximum error of <;1.4% compared to the numerical band structures.
Simulation of Semiconductor Processes and Devices (SISPAD), 2011 International Conference on; 10/2011
[show abstract][hide abstract] ABSTRACT: Highly activated n-type dopant is essential for n<sup>+</sup>/p germanium diodes which will be in use for source/drain regions in Ge n-MOSFET as the geometry scaling proceeds. This letter has investigated a combination of ion implantation of Sb in Ge and subsequent laser annealing, which resulted in highly activated Sb beyond 10<sup>20</sup> cm<sup>-3</sup>. Well-behaved Sb-doped nv/p Ge diode I-V characteristics have been demonstrated combined with TEM, SIMS, and spreading resistance profiling characterization.
IEEE Electron Device Letters 08/2011; · 2.79 Impact Factor
[show abstract][hide abstract] ABSTRACT: Highly activated n-type dopant is essential for n<sup>+</sup> /p germanium diodes which will be in use for source/drain regions in Ge n-MOSFETs as geometry scaling proceeds. Rapid thermal annealing of coimplanted P and Sb in Ge has provided n-type dopant activation beyond 1 × 10<sup>20</sup> cm<sup>-3</sup>. However, there are limited reports on the electrical characteristics of these junctions. This letter has investigated the temperature-dependent diode I-V characteristics and contact resistance of metal-n<sup>+</sup> Ge contacts. Well-behaved n<sup>+</sup> /p Ge diodes (I<sub>on</sub>/I<sub>off</sub> >; 10<sup>5</sup> and η <; 1.2) and significantly reduced contact resistance (ρ<sub>c</sub> ~ 8 × 10<sup>-7</sup> Ω · cm<sup>2</sup>) have been demonstrated.
IEEE Electron Device Letters 06/2011; · 2.79 Impact Factor
[show abstract][hide abstract] ABSTRACT: We electrically and optically characterize a germanium resonator diode on silicon fabricated by integrating a germanium light emitting diode with a microdisk cavity. Diode current-voltage characteristics show a low ideality factor and a high on/off ratio. The optical transmission of the resonator features whispering gallery modes with quality factors of a few hundred. Direct band gap electroluminescence under continuous current injection shows a clear enhancement of emission by the cavity. At this stage, the pumping level is not high enough to cause linewidth narrowing and invert the material. A higher n-type activated doping of germanium is necessary to achieve lasing.
[show abstract][hide abstract] ABSTRACT: In this paper, the acceptor and donor nature of interface traps are investigated using conductance and interface trap time constant measurements on Ge n- and p-type metal-oxide-semiconductor field-effect transistors (N-and PMOSFETs). The presence of acceptor-type interface trap states in the valence-band side of Ge band gap is confirmed by these measurements. Electron trapping by the acceptor-type interface states and their effect on Ge N- and PMOS performance are discussed. The high density of the acceptor-type interface traps found to be degrading Ge NMOSFET performance, while it is not a concern for Ge PMOSFETs because of the position of charge neutrality level in Ge. Trapped charge calculations show that reducing the interface trap density by the ozone oxidation mitigates the electron trapping by the acceptor-type traps, which otherwise degrade Ge NMOSFET performance. By engineering the gate dielectric interface of Ge NMOSFETs, 40% improvement in inversion electron mobility is reported. Improvement of 2.5× over universal hole mobility is achieved for Ge PMOSFETs.
IEEE Transactions on Electron Devices 05/2011; · 2.06 Impact Factor
[show abstract][hide abstract] ABSTRACT: Below 360°C, we demonstrate germanium (Ge) n+/p junction diode and n-channel Ge metal-oxide-semiconductor field-effect transistor (MOSFET) with a low temperature Al/Al<sub>2</sub>O<sub>3</sub>/GeO<sub>2</sub> gate stack for monolithic 3-D integration using a metal-induced dopant activation (MIDA) technique. In particular, the cobalt (Co) MIDA phenomenon is investigated on Ge damaged by an implantation process. Shallow (~100 nm) source/drain junctions with very low resistivity (5.2 × 10<sup>-4</sup> Ω-cm) are then achieved at very low temperature by the Co MIDA technique. Consequently, high diode and transistor current on/off ratios (~10<sup>4</sup> and ~10<sup>3</sup>, respectively) are obtained in this n-channel Ge MOSFET.
IEEE Electron Device Letters 04/2011; · 2.79 Impact Factor
[show abstract][hide abstract] ABSTRACT: Ge is one of the promising candidates for high-mobility channel material in future complementary metal-oxide-semiconductor technology. High-field transport in short-channel Ge p-channel field-effect transistors (PFETs) needs to be examined since device performance is determined by high-field velocity in quasi-ballistic transport regime. In this paper, ballisticity and the relationship between carrier velocity and mobility in short-channel (70-nm) Ge PFETs were thoroughly investigated. A 1.6 × -2× higher velocity was confirmed in Ge PFETs than that in Si PFETs. Uniaxial stress is also a strong performance booster besides high-mobility substrate. The effectiveness of the uniaxial stress to velocity enhancement in Ge PFETs was experimentally demonstrated in short channel regime. A 1.4× higher drive current can be achievable by uniaxially strained Ge PFET in ballistic transport regime as compared with strained Si PFET.
IEEE Transactions on Electron Devices 03/2011; · 2.06 Impact Factor