| 1. |
- Bellotti, E., et al.
(författare)
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Monte Carlo calculation of hole initiated impact ionization in 4H phase SiC
- 2000
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 87:8, s. 3864-3871
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we present a comprehensive, full band theoretical study of the high field, hole transport properties of the 4H phase of silicon carbide (4H-SiC). The calculations are performed using a full band ensemble Monte Carlo simulation that includes numerically tabulated impact ionization rates, and phonon and ionized impurity scattering rates. In addition, the simulation includes a mechanism, interband tunneling, by which the holes can move between bands in the proximity of band intersection points, It is found that there exists a significant anisotropy in the calculated steady-state hole drift velocity for fields applied parallel and perpendicular to the c-axis direction. Good agreement with experimental measurements of the hole initiated impact ionization coefficient for fields applied along the c axis is obtained, provided that interband tunneling in the proximity of band intersections is included in the model. If interband tunneling is not included, the calculated ionization coefficients are orders of magnitude lower than the experimental measurements. © 2000 American Institute of Physics.
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| 2. |
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| 3. |
- Benhamou, S, et al.
(författare)
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Meta- and pooled analyses of the effects of glutathione S-transferase M1 polymorphisms and smoking on lung cancer risk
- 2002
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Ingår i: Carcinogenesis. - : Oxford University Press (OUP). - 0143-3334 .- 1460-2180. ; 23:8, s. 1343-1350
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Tidskriftsartikel (refereegranskat)abstract
- Susceptibility to lung cancer may in part be attributable to inter-individual variability in metabolic activation or detoxification of tobacco carcinogens. The glutathione S-transferase M1 (GSTM1) genetic polymorphism has been extensively studied in this context; two recent meta-analyses of case-control studies suggested an association between GSTM1 deletion and lung cancer. At least 15 studies have been published after these overviews. We undertook a new meta-analysis to summarize the results of 43 published case-control studies including >18 000 individuals. A slight excess of risk of lung cancer for individuals with the GSTM1 null genotype was found (odds ratio (OR) = 1.17, 95% confidence interval (CI) 1.07-1.27). No evidence of publication bias was found (P = 0.4), however, it is not easy to estimate the extent of such bias and we cannot rule out some degree of publication bias in our results. A pooled analysis of the original data of about 9500 subjects involved in 21 case-control studies from the International Collaborative Study on Genetic Susceptibility to Environmental Carcinogens (GSEC) data set was performed to assess the role of GSTM1 genotype as a modifier of the effect of smoking on lung cancer risk with adequate power. Analyses revealed no evidence of increased risk of lung cancer among carriers of the GSTM1 null genotype (age-, gender- and center-adjusted OR = 1.08, 95% CI 0.98-1.18) and no evidence of interaction between GSTM1 genotype and either smoking status or cumulative tobacco consumption.
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| 4. |
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| 5. |
- Brennan, K.F., et al.
(författare)
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Monte Carlo modeling of wurtzite and 4H phase semiconductor materials
- 2001
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Ingår i: VLSI design (Print). - 1065-514X .- 1563-5171. - 0852617046 ; 13:1-4, s. 117-124
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Tidskriftsartikel (refereegranskat)abstract
- We present a discussion of the complexities encountered in particle simulation models for noncubic symmetry materials, focusing on the wurtzite and 4H phases of semiconductors. We have identified three general issues, band structure, scattering mechanisms, and band intersections, which in our opinion, constitute the most important modifications to Monte Carlo simulators for cubic symmetry materials. Owing to the increased number of atoms and size of the unit cell, the band structure is far more complex in wurtzite and 4H polytypes than in zincblende phase semiconductors. This added complexity is reflected by the greater number of bands, smaller Brillouin zone and concomitant increase in the number of band intersections. We have found that the band intersection points greatly influence the transport dynamics. In this paper, we discuss our initial attempts at treating transport near these points
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| 6. |
- Brennan, K.F., et al.
(författare)
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Monte Carlo simulation of noncubic symmetry semiconducting materials and devices
- 2000
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Ingår i: IEEE Transactions on Electron Devices. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9383. ; 47:10, s. 1882-1890
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we discuss the complexities that arise in Monte Carlo based modeling of noncubic symmetry semiconductors and their related devices. We have identified three general issues, band structure, scattering mechanisms, and band intersections that require some modification of the Monte Carlo simulator from that for cubic symmetry. Owing to the increased size and number of atoms per unit cell, the band structure is far more complex in noncubic than in zincblende phase semiconductors. This added complexity is reflected by the greater number of bands, smaller Brillouin zone and concomitant increase in the number of band intersections. We present strategies for modeling the effects of band intersections on the carrier dynamics using the Monte Carlo method. It is found that the band intersection points greatly affect the carrier transport, most dramatically in the determination of the impact ionization and breakdown properties of devices and bulk material. Excellent agreement with experimental measurements of the impact ionization coefficients is obtained only when treatment of the band intersections is included within the model.
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| 7. |
- Hjelm, Mats, et al.
(författare)
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Monte Carlo study of high-field carrier transport in 4H-SiC including band-to-band tunneling
- 2003
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 93:2, s. 1099-1107
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Tidskriftsartikel (refereegranskat)abstract
- A full-band ensemble Monte Carlo simulation has been used to study the high-field carrier transport properties of 4H-SiC. The complicated band structure of 4H-SiC requires the consideration of band-to-band tunneling at high electric fields. We have used two models for the band-to-band tunneling; one is based on the overlap test and the other on the solution of the multiband Schrodinger equations. The latter simulations have only been performed for holes in the c-axis direction, since the computer capacity requirement are exceedingly high. Impact-ionization transition rates and phonon scattering rates have been calculated numerically directly from the full band structure. Coupling constants for the phonon interaction have been deduced by fitting of the simulated low-field mobility as a function of lattice temperature to experimental data. Secondary hot electrons generated as a consequence of hole-initiated impact ionization are considered in the study for both models of band-to-band tunneling. When the multiband Schrodinger equation model is used for holes in the c-axis direction, a significant change in the electron energy distribution is found, since the hole impact-ionization rate is very much increased with this model. The secondary electrons increase the average energy of the electron distribution leading to a significant increase in the electron-initiated impact-ionization coefficients. Our simulation results clearly show that both electrons and holes have to be considered in order to understand electron-initiated impact ionization in 4H-SiC
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| 8. |
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| 9. |
- Nilsson, Hans-Erik, et al.
(författare)
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A comparison between different Monte Carlo models in simulation of hole transport in 4H-SiC
- 2001
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Ingår i: Mathematics and Computers in Simulation. - 0378-4754 .- 1872-7166. ; 55:1-3, s. 199-208
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Tidskriftsartikel (refereegranskat)abstract
- A Monte Carlo (MC) study of the hole transport in 4H-SiC is presented using three different MC models. The three models represent different approximation levels regarding band structure and scattering formulation. The most advanced model is a completely k-vector dependent full band model while the simplest model uses three analytical bands with energy dependent scattering rates. The intermediate MC model uses a full band structure calculated using a simple k.p formulation. A comparison between the models in terms of coupling constants, scattering rate, temperature dependent mobility and saturation velocity is presented
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| 10. |
- Nilsson, Hans-Erik, et al.
(författare)
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A full band Monte Carlo study of high field carrier transport in 4H-SiC
- 2000
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Ingår i: SILICON CARBIDE AND RELATED MATERIALS - 1999 PTS, 1 & 2. ; , s. 765-768
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Konferensbidrag (refereegranskat)abstract
- The high field transport properties of 4H-SiC have been studied using a bipolar full band ensemble Monte Carlo model. The impact ionization transition rates and the phonon scattering rates for both electrons and holes have been calculated numerically from the full band structure. The simulation results show a large anisotropy in the impact ionization coefficients for both electrons and holes.
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