680 research outputs found
Breakdown of universal mobility curves in sub-100-nm MOSFETs
We explore the breakdown of universal mobility behavior in sub-100-nm Si MOSFETs, using a novel three-dimensional (3-D) statistical simulation approach. In this approach, carrier trajectories in the bulk are treated via 3-D Brownian dynamics, while the carrier-interface roughness scattering is treated using a novel empirical model
Interface roughness induced intrasubband scattering in a quantum well under an electric field
Scattering rates in the lowest subband in a quantum well are calculated for interface roughness scattering when an electric field is applied normally to the layer plane. It is found that the interface roughness scattering rate increases with increasing electric field. The electric field changes the interface roughness scattering rates drastically in thick QWs as compared with those for the zero-field case
Wave function-dependent mobility and suppression of interface roughness scattering in a strained SiGe p-channel field-effect structure
The 4 K Hall mobility has been measured in a top-gated, inverted, modulation-doped Si/Si0.8Ge0.2 structure having a Si:B doping layer beneath the alloy. From comparisons with theoretical calculations, we argue that, unlike an ordinary enhancement-mode SiGe p-channel metal–oxide–semiconductor structure, this configuration leads to a decrease of interface roughness scattering with increasing sheet carrier density. We also speculate on the nature of the interface charge observed in these structures at low temperature
Intersubband absorption linewidth in GaAs quantum wells due to scattering by interface roughness, phonons, alloy disorder, and impurities
We calculate the intersubband absorption linewidth in quantum wells (QWs) due
to scattering by interface roughness, LO phonons, LA phonons, alloy disorder,
and ionized impurities, and compare it with the transport energy broadening
that corresponds to the transport relaxation time related to electron mobility.
Numerical calculations for GaAs QWs clarify the different contributions of each
individual scattering mechanism to absorption linewidth and transport
broadening. Interface roughness scattering contributes about an order of
magnitude more to linewidth than to transport broadening, because the
contribution from the intrasubband scattering in the first excited subband is
much larger than that in the ground subband. On the other hand, LO phonon
scattering (at room temperature) and ionized impurity scattering contribute
much less to linewidth than to transport broadening. LA phonon scattering makes
comparable contributions to linewidth and transport broadening, and so does
alloy disorder scattering. The combination of these contributions with
significantly different characteristics makes the absolute values of linewidth
and transport broadening very different, and leads to the apparent lack of
correlation between them when a parameter, such as temperature or alloy
composition, is changed. Our numerical calculations can quantitatively explain
the previously reported experimental results.Comment: 17 pages, including 15 figure
Effects of Interface Roughness Scattering on Radio Frequency Performance of Silicon Nanowire Transistors
The effects of an atomistic interface roughness in n-type silicon nanowire
transistors (SiNWT) on the radio frequency performance are analyzed. Interface
roughness scattering (IRS) is statistically investigated through a three
dimensional full-band quantum transport simulation based on the sp3d5s?*
tight-binding model. As the diameter of the SiNWT is scaled down below 3 nm,
IRS causes a significant reduction of the cut-off frequency. The fluctuations
of the conduction band edge due to the rough surface lead to a reflection of
electrons through mode-mismatch. This effect reduces the velocity of electrons
and hence the transconductance considerably causing a cut-off frequency
reduction
Full 3D Quantum Transport Simulation of Atomistic Interface Roughness in Silicon Nanowire FETs
The influence of interface roughness scattering (IRS) on the performances of
silicon nanowire field-effect transistors (NWFETs) is numerically investigated
using a full 3D quantum transport simulator based on the atomistic sp3d5s*
tight-binding model. The interface between the silicon and the silicon dioxide
layers is generated in a real-space atomistic representation using an
experimentally derived autocovariance function (ACVF). The oxide layer is
modeled in the virtual crystal approximation (VCA) using fictitious SiO2 atoms.
-oriented nanowires with different diameters and randomly generated
surface configurations are studied. The experimentally observed ON-current and
the threshold voltage is quantitatively captured by the simulation model. The
mobility reduction due to IRS is studied through a qualitative comparison of
the simulation results with the experimental results
n-Si/SiGe quantum cascade structures for THz emission
In this work we report on modelling the electron transport in n-Si/SiGe structures. The
electronic structure is calculated within the effective-mass complex-energy framework,
separately for perpendicular (Xz) and in-plane (Xxy) valleys, the degeneracy of which is
lifted by strain, and additionally by size quantization. The transport is described via
scattering between quantized states, using the rate equations approach and tight-binding
expansion, taking the coupling with two nearest-neighbour periods. The acoustic phonon,
optical phonon, alloy and interface roughness scattering are taken in the model. The
calculated U/I dependence and gain profiles are presented for a couple of QC structures
Stark-Effect Scattering in Rough Quantum Wells
A scattering mechanism stemming from the Stark-shift of energy levels by
electric fields in semiconductor quantum wells is identified. This scattering
mechanism feeds off interface roughness and electric fields, and modifies the
well known 'sixth-power' law of electron mobility degradation. This work first
treats Stark-effect scattering in rough quantum wells as a perturbation for
small electric fields, and then directly absorbs it into the Hamiltonian for
large fields. The major result is the existence of a window of quantum well
widths for which the combined roughness scattering is minimum. Carrier
scattering and mobility degradation in wide quantum wells are thus expected to
be equally severe as in narrow wells due to Stark-effect scattering in electric
fields.Comment: 4 pages, 2 figures with png forma
The importance of electron temperature in silicon-based terahertz quantum cascade lasers
Quantum cascade lasers (QCLs) are compact sources of coherent terahertz radiation. Although all existing QCLs use III-V compound semiconductors, silicon-based devices are highly desirable due to the high thermal conductivity and mature processing technology. We use a semiclassical rate-equation model to show that Ge/SiGe THz QCL active region gain is strongly enhanced by reducing the electron temperature. We present a bound-to-continuum QCL design employing L-valley intersubband transitions, using high Ge fraction barriers to reduce interface roughness scattering, and a low electric field to reduce the electron temperature. We predict a gain of similar to 50 cm(-1), which exceeds the calculated waveguide losses. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3237177
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