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- Nilsson, Hans-Erik, et al.
(författare)
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A semi-analytic model of the Permeable Base Transistor
- 1994
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Ingår i: Physica scripta. T. - 0281-1847. ; T54, s. 159-164
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Tidskriftsartikel (refereegranskat)abstract
- The I-V characteristics of the Permeable Base Transistor (PBT) has been investigated in order to find a simple and practical model for use in circuit designs. Two possible approaches has been discussed, a one-dimensional analytical solution and a semi-analytical solution mixing analytical and empirical methods. The semi-analytical model developed in this paper offers high accuracy and a simple and fast evaluation. All model parameters can be extracted from a set of I-V curves from two typical transistors with different threshold voltages. An analytical small signal model has been developed that agrees very well with two-dimensional simulations.
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| 3. |
- Nilsson, Hans-Erik, et al.
(författare)
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An Investigation of the blocking characteristics of the Permeable Base Transistor
- 1998
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Ingår i: Solid-State Electronics. - 0038-1101 .- 1879-2405. ; 42:3, s. 297-305
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Tidskriftsartikel (refereegranskat)abstract
- A numerical study of the blocking characteristics of the Permeable Base Transistor (PBT) is presented. The PBT is regarded as a promising transistor structure for high voltage and high frequency applications. Numerical studies of the PBT were focused on the high frequency figure of merits or the breakdown characteristics of the Schottky gate. A device designed for high frequency and high voltage switching should be optimized for large blocking and fast switching. The trade off between blocking and speed is a complicated matter which depends strongly on the geometry and doping level. In this work we studied the blocking characteristics for a Silicon PBT with regard to the doping level and doping profile, gate thickness and gate to drain distance. A scaling formalism was developed in order to estimate the transistor performance for a wide range of doping levels and geometrical combinations. A design example is presented of a normally off transistor that can block a drain to source voltage of 10 V while the unity current gain frequency fT value for Vgs = 0.2 V is higher than 7 GHz.
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| 4. |
- Nilsson, Hans-Erik, et al.
(författare)
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Different methods of noise reduction in Monte Carlo simulations of a Schottky diode
- 1994
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Ingår i: Physica scripta. T. - 0281-1847. ; T54, s. 268-272
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Tidskriftsartikel (refereegranskat)abstract
- Methods of decreasing the noise and increasing the computational efficiency in Monte Carlo simulations of semiconductor devices are investigated. A lookup table approach to the charge assignment to mesh points has been implemented which is independent of the complexity of the assignment function. Using this approach reduces the CPU time of the charge assignment to about one third. Potential fluctuations in low field regions are compared for different assignment function, which shows the advantage of using more complex schemes than those generally used. Results from a full band Monte Carlo simulation of a submicron Schottky diode are presented and the values of the current density for different assignment schemes are compared, showing a lower noise for the higher order schemes. Statistical enhancements by splitting of superparticles in the depletion region has been investigated. The combination of a high order assignment scheme and statistical enhancement by splitting decreases simulation runtimes considerable for a given noise tolerance.
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| 7. |
- Nilsson, Hans-Erik, et al.
(författare)
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Monte Carlo simulation of high field hole transport in 4H-SiC including band to band tunneling and optical interband transisitons
- 2002
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Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 314:1-4, s. 68-71
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Tidskriftsartikel (refereegranskat)abstract
- The high field hole transport in 4H-SiC has been studied using a full band Monte Carlo (MC) simulation model that includes band to band tunneling and allows mixing of the band states during carrier drift. Impact ionization coefficients along the c-axis direction have been extracted and compared with experimental data. It is shown that the band to band tunneling mechanism is crucial in order to explain experimental results. The carrier distribution function obtained from the MC simulations has been used to determine the breakdown luminescence spectra coming from interband transitions. Our results are in good agreement with the available experimental luminescence spectra for SiC polytypes, and the importance of including interband tunneling is clearly demonstrated.
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| 8. |
- Nilsson, Hans-Erik, et al.
(författare)
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Numerical modeling of hole interband tunneling in wurtzite GaN and SiC
- 2001
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 90:6, s. 2847-2852
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Tidskriftsartikel (refereegranskat)abstract
- The time evolution of Bloch electrons (holes) moving in a constant electric field has been studied for GaN and 2H-SiC using a numerical model based on realistic band structures. The large band gap of GaN and the SiC polytypes provide much larger critical fields than in conventional semiconductors, which allows device operation at very high electric fields. At sufficiently high electric fields the carriers may change band during drift due to tunneling. GaN has a direct band gap, while the hexagonal SiC polytypes have indirect band gaps. In spite of this difference the valence band structure is very similar due to the wurtzite symmetry. In this work the GaN and the 2H-SiC polytype are considered as wurtzite prototype semiconductors in order to study valence band to band tunneling in wurtzite semiconductors for electric fields directed along the c axis. A large valence band to band tunneling probability was found for both materials at electric fields above 400 kV/cm. This shows the importance of considering band to band tunneling in studies of high field hole transport in wide band-gap hexagonal semiconductor materials. The proposed numerical approach can be used to enhance the interband tunneling models used in Monte Carlo simulation of carrier transport in hexagonal semiconductors.
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| 9. |
- Nilsson, Hans-Erik, et al.
(författare)
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Numerical study of Bloch electron dynamics in wide band-gap semiconductors
- 2001
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Ingår i: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 184:1-4, s. 199-203
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we are using numerical calculations to demonstrate the importance of band to band tunneling in wide band-gap semiconductors. We have considered 4H-SiC, 3C-SiC and wurtzite GaN as prototype semiconductors in the demonstration. Wide band-gap semiconductors allow device operation under very high-applied electric fields, where significant band to band tunneling is expected to occur. Hexagonal wide band-gap semiconductors have a valence band structure with a large number of bands separated by rather small energies. Our calculation shows that this leads to a very significant band to band tunneling even at relatively low electric fields. In cubic wide band-gap semiconductors the tunneling is much less pronounced. However, at the valence band maximum the band separations are small enough to allow significant band to band tunneling. The spin-orbit interaction tends to bend the band near the maximum creating degradation from a parabolic curvature. This bending is found to significantly influence the band to band tunneling process. © 2001 Elsevier Science B.V. All rights reserved.
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