Carrier Transport and Velocity Overshoot in Strained Si On Sige Heterostructures

1998 ◽  
Vol 533 ◽  
Author(s):  
David K. Ferry ◽  
Gabriele Formicone ◽  
Dragica Vasileska
Keyword(s):  
Monte Carlo ◽  
Enhancement Factor ◽  
Carrier Transport ◽  
State Of The Art ◽  
Carrier Dynamics ◽  
Device Performance ◽  
Short Channel ◽  
Strained Si ◽  
Velocity Overshoot ◽  
Ensemble Monte Carlo

AbstractWe examine the velocity overshoot effect in strained Six on Six-Ge1-x heterostructures. We also investigate the performance of surface-channel strained-Si MOSFETs for devices with gate lengths representative of the state-of-the-art technology. The Ensemble Monte Carlo method, self-consistently coupled with the 2D Poisson equation solver, is used in the investigation of the device performance. Our simulations suggest that, in short-channel devices, velocity overshoot is very important. In fact, when velocity overshoot occurs, it greatly affects the carrier dynamics and the current enhancement factor of both surface-channel strained-Si and conventional Si MOSFETs.

A Multiscale Modeling Approach to Study Transport in Silicon Heterojunction Solar Cells

2016 ◽  
Vol 2016 (DPC) ◽  
pp. 002095-002110 ◽  
Author(s):  
Pradyumna Muralidharan ◽  
Stuart Bowden ◽  
Stephen M. Goodnick ◽  
Dragica Vasileska
Keyword(s):  
Monte Carlo ◽  
Solar Cells ◽  
Solar Cell ◽  
Amorphous Silicon ◽  
Buffer Layer ◽  
Kinetic Monte Carlo ◽  
Device Performance ◽  
Drift Diffusion ◽  
Heterojunction Solar Cells ◽  
Ensemble Monte Carlo

Single junction solar cells based on Silicon continue to be relevant and commercially successful in the market due to their high efficiencies and relatively low cost processing. Heterojunction solar cells based on crystalline (c-Si) and amorphous (a-Si) silicon (HIT Cells) have paved the way for devices with high VOC's (>700 mV) and high efficiencies (>20%) [1]. Panasonic currently holds the world record efficiency of 25.6% for its trademark a-Si/c-Si HIT cell [2]. The novel structure of the device precludes the usage of traditional methods (such as drift diffusion) to accurately understand the nature of transport. Theoretical models used by commercial simulators make a variety of assumptions that simplifies the transport problem (assumes a Maxwellian distribution of carriers) and thus lacks the sophistication to study defect transport. In this work we utilize a combination of Ensemble Monte Carlo (EMC) simulations, Kinetic Monte Carlo (KMC) simulations and traditional drift - diffusion (DD) simulations to study transport in the heterojunction solar cell. The device performance of an amorphous silicon (a-Si)/crystalline silicon (c-Si) solar cell depends strongly on the interfacial transport properties of the device [3]. The energy of the photogenerated carriers at the barrier strongly depends on the strength of the inversion at the heterointerface and their collection requires interaction with the defects present in the intrinsic amorphous silicon buffer layer [4]. In this work we present a multiscale model which can bridge the gap in time scales between different microscopic processes to study the transport through the interface by coupling an ensemble Monte Carlo (EMC) and a kinetic Monte Carlo (KMC). The EMC studies carrier properties such as the energy distribution function (EDF) at the heterointerface whereas the KMC method allows us to simulate the interaction of discrete carriers with discrete defects [5]. This method allows us to study defect transport which takes place on a time scale which is too long for traditional ensemble Monte Carlo's to analyze. We analyze the injection and extraction of carriers via defects by calculating transition rates for different processes. By using the principles of SRH recombination, this method can also be extended to study recombination processes at the interface and in the amorphous bulk which are crucial parameters for solar cell performance. Therefore, by using the multiscale approach all important processes can be studied rigorously to evaluate device performance. Our simulations indicate that a phonon assisted emission process from a defect is the most favored extraction mechanism and both Poole-Frenkel emission (<2%) and thermionic emission (<1%) were not significant. We extended our simulation methodology to study recombination at the interface and in the buffer layer of the device to find that the device performance is mainly interface recombination limited and that defect densities in the buffer layer have to be really high (>1018 cm-3) in order to degrade device performance.

Ultra-short n-MOSFETs with strained Si: device performance and the effect of ballistic transport using Monte Carlo simulation

2006 ◽  
Vol 21 (4) ◽  
pp. 422-428 ◽  
Author(s):  
Valérie Aubry-Fortuna ◽  
Arnaud Bournel ◽  
Philippe Dollfus ◽  
Sylvie Galdin-Retailleau
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Ballistic Transport ◽  
Device Performance ◽  
Strained Si

MONTE-CARLO SIMULATION OF ULTRA-THIN FILM SILICON-ON-INSULATOR MOSFETs

2013 ◽  
Vol 22 (01) ◽  
pp. 1350001
Author(s):  
FRANCISCO GÁMIZ ◽  
CARLOS SAMPEDRO ◽  
LUCA DONETTI ◽  
ANDRES GODOY
Keyword(s):  
Monte Carlo ◽  
Ground Plane ◽  
Silicon On Insulator ◽  
Slab Thickness ◽  
Short Channel ◽  
Fully Depleted ◽  
Ensemble Monte Carlo ◽  
Soi Devices ◽  
Monte Carlo Simulator ◽  
The Impact

State-of-the-Art devices are approaching to the performance limit of traditional MOSFET as the critical dimensions are shrunk. Ultrathin fully depleted Silicon-on-Insulator transistors and multi-gate devices based on SOI technology are the best candidates to become a standard solution to overcome the problems arising from such aggressive scaling. Moreover, the flexibility of SOI wafers and processes allows the use of different channel materials, substrate orientations and layer thicknesses to enhance the performance of CMOS circuits. From the point of view of simulation, these devices pose a significant challenge. Simulations tools have to include quantum effects in the whole structure to correctly describe the behavior of these devices. The Multi-Subband Monte Carlo (MSB-MC) approach constitutes today's most accurate method for the study of nanodevices with important applications to SOI devices. After reviewing the main basis of MSB-MC method, we have applied it to answer important questions which remain open regarding ultimate SOI devices. In the first part of the chapter we present a thorough study of the impact of different Buried OXide (BOX) configurations on the scaling of extremely thin fully depleted SOI devices using a Multi-Subband Ensemble Monte Carlo simulator (MS-EMC). Standard thick BOX, ultra thin BOX (UTBOX) and UTBOX with ground plane (UTBOX+GP) solutions have been considered in order to check their influence on short channel effects (SCEs). The simulations show that the main limiting factor for downscaling is the DIBL and the UTBOX+GP configuration is the only valid one to downscale SGSOI transistors beyond 20 nm channel length keeping the silicon slab thickness above the theoretical limit of 5 nm, where thickness variability and mobility reduction would play an important role. In the second part, we have used the multisubband Ensemble Monte Carlo simulator to study the electron transport in ultrashort DGSOI devices with different confinement and transport directions. Our simulation results show that transport effective mass, and subband redistribution are the main factors that affect drift and scattering processes and, therefore, the general performance of DGSOI devices when orientation is changed

scholarly journals Monte Carlo Calibrated Drift-Diffusion Simulation of Short Channel HFETs

VLSI Design ◽  
1998 ◽  
Vol 8 (1-4) ◽  
pp. 319-323
Author(s):  
A. Asenov ◽  
S. Babiker ◽  
S. P. Beaumont ◽  
J. R. Barker
Keyword(s):  
Monte Carlo ◽  
Mobility Model ◽  
Channel Length ◽  
Drift Diffusion ◽  
Short Channel ◽  
Velocity Overshoot ◽  
Saturation Velocity ◽  
Mc Simulation ◽  
Diffusion Simulation ◽  
Good Agreement

In this paper we present a methodology to use drift diffusion (DD) simulations in the design of short channel heterojunction FETs (HFETs) with well pronounced velocity overshoot. In the DD simulations the velocity overshoot in the channel is emulated by forcing the saturation velocity in the field dependent mobility model to values corresponding to the average velocity in the channel obtained from Monte Carlo (MC) simulation. To illustrate our approach we compare enhanced DD and MC simulation results for a pseudomorphic HEMTs with 0.12 μm channel length, which are in good agreement. The usefulness of the described methodology is illustrated in a simulation example of self aligned gamma gate pseudomorphic HEMTs. The effect of the gamma gate shape and the self aligned contacts on the overall device performance has been investigated.

Ensemble Monte Carlo analysis of subpicosecond transient electron transport in cubic and hexagonal silicon carbide for high power SiC-MESFET devices

2015 ◽  
Vol 29 (16) ◽  
pp. 1550107 ◽  
Author(s):  
Youcef Belhadji ◽  
Benyounes Bouazza ◽  
Fateh Moulahcene ◽  
Nordine Massoum
Keyword(s):  
Silicon Carbide ◽  
Monte Carlo ◽  
High Temperature ◽  
Electron Transport ◽  
Band Structure ◽  
Monte Carlo Analysis ◽  
Structure Model ◽  
Velocity Overshoot ◽  
Ensemble Monte Carlo ◽  
Band Structure Model

In a comparative framework, an ensemble Monte Carlo was used to elaborate the electron transport characteristics in two different silicon carbide (SiC) polytypes 3C-SiC and 4H-SiC. The simulation was performed using three-valley band structure model. These valleys are spherical and nonparabolic. The aim of this work is to forward the trajectory of 20,000 electrons under high-flied (from 50 kV to 600 kV) and high-temperature (from 200 K to 700 K). We note that this model has already been used in other studies of many Zincblende or Wurtzite semiconductors. The obtained results, compared with results found in many previous studies, show a notable drift velocity overshoot. This last appears in subpicoseconds transient regime and this overshoot is directly attached to the applied electric field and lattice temperature.

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