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H Morkoc - One of the best experts on this subject based on the ideXlab platform.
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Base Transit Time of gan ingan heterojunction bipolar transistors
Journal of Applied Physics, 1995Co-Authors: S N Mohammad, H MorkocAbstract:A theoretical analysis of the Base Transit Time in npn GaN/InGaN heterojunction bipolar transistor has been performed. For the analysis the effect of band‐gap narrowing, carrier degeneracy, and compositional grading of the Base region has been considered. The analysis demonstrates that a nonuniform doping in the Base region with a higher value at the emitter edge and a lower value at the collector edge together with a compositional grading is necessary for minimizing the Base Transit Time.
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influence of nonuniform doping on the uniformity of current gain Base Transit Time and related properties of algaas gaas heterojunction bipolar transistors
Journal of Applied Physics, 1995Co-Authors: S N Mohammad, Jeninn Chyi, J Chen, H MorkocAbstract:An experimental investigation of the effect of doping concentration variation on the uniformity of current gain as a function of collector current of AlGaAs/GaAs heterojunction bipolar transistors (HBT) has been performed. An analysis of the Gummel plots for these HBTs has also been carried out to understand the physics underlying their operations. The study demonstrates that an optimized doping gradient both in the emitter and the Base results not only in a uniform current gain with respect to collector current but also leads to a suppression of emitter size effects encountered in the scaling down of transistors. Numerical simulations suggest that the generation of an electric field in the Base region of an HBT due to nonuniform Base doping leads apparently to no lowering of the Base Transit Time.
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Base Transit Time for sige Base heterojunction bipolar transistors
Electronics Letters, 1991Co-Authors: G B Gao, H MorkocAbstract:The Base Transit Time expressions for SiGe Base heterojunction bipolar transistors are presented including the accelerating field effects due to the Base bandgap grading and doping grading, and the retarding field (opposing drift field) effect from the graded boron profile down towards the emitter. It is found that the retarding field exhibits 40–80% contribution to the Base Transit Time, depending on the boron concentration near the emitter. The results of Base Transit Time from these analytic expressions are unambiguously supported by the published simulation data.
K. Suzuki - One of the best experts on this subject based on the ideXlab platform.
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Optimum Base-doping profile for minimum Base Transit Time considering velocity saturation at Base-collector junction and dependence of mobility and bandgap narrowing on doping concentration
IEEE Transactions on Electron Devices, 2001Co-Authors: K. SuzukiAbstract:We used variational calculus, the trial function, and the iterative procedure method to evaluate the optimum Base doping concentration profile that will yield the minimum Base Transit Time /spl tau//sub B/. All methods were extended to include the velocity saturation at the Base collector junction, and the dependence of mobility and bandgap narrowing on the Base doping concentration. We showed that all methods produce almost the same /spl tau//sub B/, although the profiles differ. Among them, the iterative method always produces the minimum /spl tau//sub B/ and variational calculus clearly shows the dependence of /spl tau//sub B/ on physical parameters.
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analytical Base Transit Time model for high injection regions
Solid-state Electronics, 1994Co-Authors: K. SuzukiAbstract:Abstract Using a perturbation theory focused on injected electron concentrations, we derived analytical models for collector current density, J n , and Base Transit Time, τ B , for arbitrarily doped Bases. These models are valid in all injection regions before the onset of the Kirk effect, include existing models as special cases, and agree well with numerical results. Our model predicts that τ B for the Gaussian-doped Base is still smaller than that of a Base with a uniform profile, a box-doped Base, even in high-injection regions.
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Base Transit Time of shallow-Base bipolar transistors considering velocity saturation at Base-collector junction
IEEE Transactions on Electron Devices, 1992Co-Authors: K. Suzuki, N. NakayamaAbstract:The authors studied the influence of the velocity saturation in the Base-collector depletion layer and compared the injected electron concentration profile, collector current density, and Base Transit Time with velocity saturation to those without. The collector current with velocity saturation is only a little smaller than the current without saturation, but the injection electron concentration profile changes substantially when comparing currents with and without velocity saturation. The Base Transit Time is increased by velocity saturation, and the ratio of Base Transit Time with velocity saturation to that without velocity saturation increases as the Base width decreases. Thus, velocity saturation must be considered in order to evaluate the Base Transit Time of shallow-Base bipolar transistors. The dependence of the Base Transit Time on the doping profile was also analyzed, revealing that the Base Transit Time of a box doping profile is increased more than that of a Gaussian doping profile.
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analytical collector current density and Base Transit Time models for high injection regions
1992Co-Authors: K. SuzukiAbstract:Using perturbation theory focused on modulated electric fields due to injected electrons, we derived analytical models for collector current density. Jn, and Base Transit Time, T~, for arbitrarily doped Bases. These models are the first valid for arbitrary injection levels before the onset of the Kirk effect. and they include existing models as special cases. Our model predicts that zB for the Gaussian-doped Base is still smaller than that for the box-doped Base wen in high-injection regions.
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Emitter and Base Transit Time of polycrystalline silicon emitter contact bipolar transistors
IEEE Transactions on Electron Devices, 1991Co-Authors: K. SuzukiAbstract:The author formulates Transit Time in the neutral emitter region, tau /sub E/, and in the neutral Base region tau /sub B/, of polycrystalline silicon emitter contact bipolar transistors. An analytical theory derived for tau /sub E/ of polysilicon emitter contact bipolar transistors and its dependence on the emitter junction depth, the polysilicon thickness, and the Base width are presented. The influence of bandgap narrowing on tau /sub E/ and tau /sub B/ is analyzed. Bandgap narrowing increases tau /sub E/, but tau /sub B/ is insensitive to it. tau /sub E/ is proportional to Base width W/sub B/ and tau /sub B/ to W/sup 2//sub B/. tau /sub E/ is not negligible compared to tau /sub B/ when W/sub B/ is less than 100 nm. Reducing emitter junction depth and polysilicon thickness is indispensable to developing shallow Base bipolar transistors. >
M Shahidul M Hassan - One of the best experts on this subject based on the ideXlab platform.
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analytical modeling of Base Transit Time considering recombination in the non uniformly doped Base
2011 International Symposium on Humanities Science and Engineering Research, 2011Co-Authors: Md Iqbal Bahar Chowdhury, M Shahidul M HassanAbstract:The main objective of this paper is to show that recombination in the Base needs to be taken into account in determining Base Transit Time τB. In previous analytical works for τB, recombination in the Base was neglected. In this paper both drift and diffusion currents for electron and hole are considered in obtaining minority carrier profile n(x). In the model, both SRH and Auger recombination are considered. The energy-bandgap-narrowing effects due to heavy doping, velocity saturation as well as doping and field dependent mobility are considered. The model shows that recombination has significant effects on the Base Transit Time of a heavily doped Base.
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Base Transit Time of a heterojunction bipolar transistor with gaussian doped Base
International Conference on Electrical and Control Engineering, 2010Co-Authors: S Moududul M Islam, Yeasir Arafat, Iqbal Bahar Chowdhury, Ziaur Rahman M Khan, M Shahidul M HassanAbstract:Base Transit Time for an npn SiGe HBT is calculated assuming Gaussian doped Base and a generalized trapezoidal Ge profile considering field dependent mobility in excess to doping dependent mobility and diffusivity. Band-gap narrowing (BGN) due to heavy doping, due to presence of Ge and due to change in the density of states (DOS) are also considered. For presence of Ge, a different saturation velocity has been used. Ge profile variation has been incorporated by a single parameter. Base Transit Time of SiGe HBT is calculated and computed for different Ge contents. The calculated Base Transit Time shows similar variations as found in literature for BJT.
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analysis of Base Transit Time for a bipolar junction transistor considering Base current
International Conference on Electrical and Control Engineering, 2010Co-Authors: Md Iqbal Bahar Chowdhury, M Shahidul M HassanAbstract:Consideration of Base current makes the analytical modeling of Base Transit Time for a bipolar junction transistor intractable, as such model requires knowledge of the majority hole current density, the recombination mechanism in the Base and the injection of carriers from the Base contact. All these effects along with bandgap narrowing, velocity saturation, Webster effect etc. makes the differential equation for minority carrier density third order or higher, nonlinear, non-homogeneous and of variable-coefficient. In this work, all these difficulties have been successfully overcome and therefore, an analytical model has been developed. The model results show that the consideration of Base current increases the Base Transit Time up to 5 – 8% even in the low-injection condition.
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analytical modeling of Base Transit Time for a si 1 y ge y heterojunction bipolar transistor
International Conference on Electron Devices and Solid-State Circuits, 2009Co-Authors: Yeasir Arafat, Md Ziaur Rahman Khan, M Shahidul M HassanAbstract:An analytical model for Base Transit Time of an exponentially doped Base npn Si 1−y Ge y HBT has been developed. The model is valid in all levels of injection before the onset of Kirk effect. In this analysis, bandgap-narrowing effect, high-injection effect, carrier velocity saturation at the Base edge of the Base collector junction and doping dependent mobility are incorporated. It is found that Base Transit Time depends on the Ge profiles in the Base. The increase of Ge content for the same profile results in a decrease of Transit Time. Results of this work are compared with results available in literature.
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a new technique for determining Base Transit Time of a bipolar junction transistor
International Conference on Electrical and Control Engineering, 2006Co-Authors: Md W K Nomani, M Shahidul M HassanAbstract:A Base Transit Time model for an npn bipolar junction transistor with exponential-doped Base at high level of injection, which is applicable for all levels of injection before the onset of the Kirk effect, is developed. Based on the realistic assumption that a small change in electron concentration in the Base at high injection occurs from its modified low injection model incorporating Webster effect, mathematical expressions for minority carrier concentration and current density have been derived. In this work, electric field dependence of mobility in addition to doping dependent mobility, bandgap-narrowing effect, high-injection effect and carrier velocity saturation at the Base edge of the Base-collector junction are incorporated. The Base Transit Time is found to be different if the field dependent mobility is considered. The analytically calculated Base Transit Time is found to be in good agreement with numerical results available in literature.
A F M Anwar - One of the best experts on this subject based on the ideXlab platform.
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Base Transit Time in abrupt gan ingan gan hbt s
IEEE Transactions on Electron Devices, 2000Co-Authors: S Y Chiu, A F M AnwarAbstract:Base Transit Time in an abrupt GaN/InGaN/GaN HBT is reported. Temperature and doping concentration dependence of low field mobility is obtained from an ensemble Monte Carlo simulation. Base Transit Time, /spl tau//sub b/, decreases with increasing temperature. The low temperature /spl tau//sub b/ is dominated by the diffusion constant or, in other words, transport within the neutral Base region. However, at elevated temperatures Base Transit Time is dependent more upon the Base-collector junction velocity or, in other words, by the transport across the heterointerface. /spl tau//sub b/ increases with In-mole fraction showing a stronger dependence at lower temperatures. Unity gain current cut-off frequency, f/sub T/, is a strong function of temperature and Base doping concentration. An f/sub T/ of 20 GHz is obtained for a 0.05 /spl mu/m HBT.
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Base Transit Time in abrupt gan ingan gan and algan gan algan hbts
Mrs Internet Journal of Nitride Semiconductor Research, 1999Co-Authors: Sheanyih Chiu, A F M AnwarAbstract:Base Transit Time, τb, in abrupt npn GaN/InGaN/GaN and AlGaN/GaN/AlGaN double heterojunction bipolar transistors (DHBTs) is reported. Base Transit Time strongly depends not only on the quasi-neutral Base width, but also on the low field electron mobility, μn, in the neutral Base region and the effective electron velocity, Sc, at the edge of Base-collector heterojunction. μn and Sc are temperature-dependent parameters. A unity gain cut-off frequency of 10.6 GHz is obtained in AlGaN/GaN/AlGaN DHBTs and 19.1 GHz in GaN/InGaN/GaN DHBTs for a neutral Base width of 0.05um. It is also shown that non-stationary transport is not required to study τb for neutral Base width in the range of 0.05um for GaN-Based HBTs.
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an exact current partitioning and its effect on Base Transit Time in double heterojunction bipolar transistors
Solid-state Electronics, 1996Co-Authors: M M Jahan, A F M AnwarAbstract:Abstract The current transport across the abrupt Base-collector heterojunction of double heterojunction bipolar transistors (DHBTs) has been studied by partitioning the total collector current into thermionic and tunneling components within a unified formulation. An exact quantum mechanical calculation, including image force lowering of the potential energy barrier, is performed in calculating the total current. A modified junction velocity is calculated and compared with previously reported results. It is shown that the estimation of junction velocity using the previously reported simplified calculation severely underestimated tunneling, especially at low reverse bias. The modified junction velocity is used to study the Base Transit Time of DHBTs.
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an analytical expression for Base Transit Time in an exponentially doped Base bipolar transistor
Solid-state Electronics, 1996Co-Authors: M M Jahan, A F M AnwarAbstract:Abstract An analytical expression of Base Transit Time for exponentially doped Base, which is applicable to both homojunction and heterojunction bipolar transistors, is developed. The present treatment includes dopant dependent mobility variation, bandgap narrowing and finite velocity saturation effects in the calculation of Base Transit Time and thus is a generalization of the results reported recently by Rosenfield and Alterovitz[6]. These effects degrade Base Transit Time significantly and must be incorporated in the calculation. the finite velocity saturation effect will progressively play a pivotal role as the Base width is scaled down and for double heterostructure bipolar transistor. The Transition of Base Transit Time from the ballistic and the drift-diffusion limit will occur at a longer Base width if the Base is exponentially doped with a sufficiently high doping index.
S N Mohammad - One of the best experts on this subject based on the ideXlab platform.
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Base Transit Time of gan ingan heterojunction bipolar transistors
Journal of Applied Physics, 1995Co-Authors: S N Mohammad, H MorkocAbstract:A theoretical analysis of the Base Transit Time in npn GaN/InGaN heterojunction bipolar transistor has been performed. For the analysis the effect of band‐gap narrowing, carrier degeneracy, and compositional grading of the Base region has been considered. The analysis demonstrates that a nonuniform doping in the Base region with a higher value at the emitter edge and a lower value at the collector edge together with a compositional grading is necessary for minimizing the Base Transit Time.
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influence of nonuniform doping on the uniformity of current gain Base Transit Time and related properties of algaas gaas heterojunction bipolar transistors
Journal of Applied Physics, 1995Co-Authors: S N Mohammad, Jeninn Chyi, J Chen, H MorkocAbstract:An experimental investigation of the effect of doping concentration variation on the uniformity of current gain as a function of collector current of AlGaAs/GaAs heterojunction bipolar transistors (HBT) has been performed. An analysis of the Gummel plots for these HBTs has also been carried out to understand the physics underlying their operations. The study demonstrates that an optimized doping gradient both in the emitter and the Base results not only in a uniform current gain with respect to collector current but also leads to a suppression of emitter size effects encountered in the scaling down of transistors. Numerical simulations suggest that the generation of an electric field in the Base region of an HBT due to nonuniform Base doping leads apparently to no lowering of the Base Transit Time.