• Journal of the Korea Institute of Information and Communication Engineering
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• v.3 no.4
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• pp.915-922
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• 1999

The field dependent characteristics of electron transport with GaAs impact ionization have been analyzed, using GaAa full band E-k relationship. The E-k relationship is derived from empirical pseudopotential method, using Fermi's golden rule and local form factor, and Brillouin zone is divided into tetrahedrons for calculating impact ionization rate, and tetrahedron method, in which integrates each tetrahedrons, is used. Monte Carlo simulation is used for analyzing anisotropy of impact ionization. A result of transient analysis for impact ionization has presented that anisotropy of impact ionization only arises during transient state and impact ionization is isotropic under steady state. Anisotropic characteristics of impact ionization for GaAs, which is presented in this paper, can be used in carrying out a transient analysis for GaAs devices.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.3
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• pp.697-703
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• 2000

As device dimensions are lastly scaled down, impact ionization(I.I.) events are very important to analyze hot carrier transport in high energy region, and the exact model of impact ionization is demanded on device simulation. We calculate full band model by empirical pseudopotential method and the impact ionization rate is derived from modified Keldysh formula. We calculate impact ionization coefficients by full band Monte Carlo simulator to investigate temperature dependent characteristics of impact ionization for GaAs as a function of field. Resultly impact ionization coefficients are in good agreement with experimental values at look. We how energy is increasing along increasing the field, while energy is decreasing along increasing the temperature since the phonon scattering rates for emission mode are very high at high temperature. The logarithmic fitting function of impact ionization coefficients is described as a second orders function of temperature and field. The residuals of the logarithmic fitting function are mostly within 5%. We Dow, therefore, the logarithm of impact ionization coefficients has quadratic dependence on temperature, and we can save time of calculating the temperature dependent impact ionization coefncients as a function of field.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2000.05a
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• pp.460-464
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• 2000

As device dimensions are lastly scaled down, impact ionization(I.I.) events are very important to analyze hot carrier transport in high energy region, and the exact model of impact ionization is demanded on device simulation. We calculate full band model by empirical pseudopotential method and the impact ionization rate is derived from modified Keldysh formula. We calculate impact ionization coefficients by full band Monte Carlo simulator to investigate temperature-and field-dependent characteristics of impact ionization for GaAs. Resultly impact ionization coefficients are In good agreement with experimental values at 300k. We know energy is increasing along increasing the field. while energy is decreasing along increasing the temperature since the phonon scattering rates for omission mode are very high at high temperature. The logarithmic fitting function of impact ionization coefficients is described as a second orders function for temperature and field. The residuals of the logarithmic fitting function are mostly within 5%. We know, therefore, logarithm of impact ionization coefficients has quadratic dependence on temperature and field, and we can save time of calculating the temperature- and field-dependent impact ionization coefficients.

• Proceedings of the KIEE Conference
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• 1989.11a
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• pp.131-135
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• 1989

Hot electron simulation of silicon using Monte Carlo method was carried out to investigate impact ionization characteristics near the drain of MOSFET's at 77 and 300K. We successfully characterized drift velocity and impact ionization at 77 and 300K employing a simplified energy band structure and phonon scattering mechanisms. Woods' soft energy threshold model was introduced to the Monte Carlo simulation of impact ionization, and good agreement with reported experimental results was resulted by employing threshold energy of 1.7 eV. It is suggested that the choice of the critical angle between specular reflection and diffusive scattering of surface roughness scattering may be important in determining the impact ionization charateristics of Monte Carlo simulation near the drain of MOSFET's.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.11
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• pp.112-119
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• 1996

Impact ionization model in GaAs has been presented by modified keldysh formula with two sets of power exponent of 7.8 and 5.6 in study. Impact ionization rate is derived from fermil's golden rule and ful lenergy band stucture based on empirical pseudopotential method. Impact ionization rates show anisotropic property in low energy region (<3eV), but isotropic in high energy region (3>eV). Full band monte calo simulator is coded for investigating the validity of the GaAs impact ionization model, and validity is checked by comparing impact ionization coefficients with experimental values and ones in anisotropic model. Valley transitions to energy alteration are explained by investigating electron motion in brillouin zone for full band model to electric field variation.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.11a
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• pp.520-524
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• 1999

The Impact ionization rate is highly anisotropic at low electron energy, while it becomes isotropic at higher energy range in which impact ionization events frequently accur. In this study, full energy band structure obtained by pseudopotential method and Fermi's golden rule is used to calculate impact ionization rate. The calculated impact ionization rate is well fitted to a modified Keldysh formular at 300K and 77K. Full band Monte Carlo simulator is made to investigate the validity of the GaAs impact ionization coefficients at 300K and 77K. Impart ionization process is isotropic under the condition of steady state since anisotrophy appears during very short time at look. Impart ionization coefficients is nearly constant and is anisotropic in electric field applied along the <110> direction at 77K.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2000.05a
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• pp.451-454
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• 2000

The impact ionization(I.I.) is necessary to analyze carrier transport properties under the influence of high electric field. The full band I-k relation and Fermi's golden rule are used for the calculation of impact ionization rate. We have investigated the temperature- and field-dependent impact ionization coefficient for silicon using full band Monte Carlo simulation. The impact ionization coefficients calculated by our impact ionization model are agreed with experimental data at look. We know that impact ionization coefficients and electron energies are decreasing along increasing temperature due to increase of phonon scattering, especially by emission. The logarithm of impact ionization coefficients are fitted to linear function for temperature and field. The residuals of linear function are within the error bound of 5%. We know logarithmic impact ionization coefficients are linearly dependent on temperature and field.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.05a
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• pp.389-393
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• 1999

The exact model of impact ionization events in which has influence on device efficiency, is to be necessary element for device simulation. Recently, a modified Keldysh formula with two set of power exponent of 7.8 and 5.6 is used to simulate carrier transport. This model is, however, not suitable as impact ionization model in low energy range since this ignore direction dependent properties of impact ionization. The impact ionization rate is highly anisotropic at low energy, while it becomes isotropic at higher energy range. Note that impact ionization events frequently occur in high energy range. For calculating impart ionization rate, we use full energy band structure derived from Fermi's golden rule and empirical pseudopotential method. We compare with calculated and experimental value, and investigate direction dependent conduction energy band structure along the direction of <100>, <110> and <111>. We know that the threshold energy of impact ionization is anisotropic and impact ionization rate is very deviated from modified Keldish formula, in relatively low energy range.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.4
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• pp.121-128
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• 1996

The impact ionization rate of thethighly-doped AlGaAs/GaAs quantum well structure is calculated, which is an important parameter ot design theinfrared detector APD and the novel neural device. In conjunction with ensemble monte carlo method and quantum mechanical treatment, we analyze the effects of the parameters of quantum well structure on the impact ionization rate. Since the number of the occupied subbands increases while the energy of the subbands decreases as the width of quantum well increases, the impact ionization rate increases in the range of th esmall well width but gradually the increament slows down and is finally saturated. Due to the effect of the energy of the injected electrons into the quantum well and the tunneling through the barrier, the impact ionization rate increases for the range of the small barrier width and decreases for the range of the large barrier width. Thus, there exists a barrier width to maximize the impact ionzation rate for a mole fraction x, and the barrier width moves to the larger vaue as the mole fraction x increases. The impact ionization rate is much more sensitive to the variation of the doping density than that of the other quantum well parameters. We found that there is a limit of the doping density to confine the electronics in the quantum well effectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.105-106
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• 2005

The impact ionization MOS (I-MOS) transistor with 50nm channel length is presented by using 2-D device simulator ISE-TCAD. The subthreshold slope cannot be steeper than kT/q since the subthreshold conduction is due to diffusion current. As MOSFETs are scaled down, this problem becomes significant and the subthreshold slope degrades which leads an increase in the off-current and off-state power dissipation. The I-MOS is based on a gated p-i-n structure and the subthreshold conduction is induced by impact ionization. The simulation results show that the subthreshold slope is 11.7 mV/dec and this indicates the I-MOS improves the switching speed and off-state characteristics.