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MONTE CARLO SIMULATIONS OF IMPACT IONIZATION AND LOCK-ON IN GaAs

MONTE CARLO SIMULATIONS OF IMPACT IONIZATION AND LOCK-ON IN GaAs. Samsoo Kang and Charles W. Myles Department of Physics Texas Tech University Harold P. Hjalmarson Sandia National Laboratories SK and CWM supported in part by Texas Advanced Research Program Grant No. 003644-047

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MONTE CARLO SIMULATIONS OF IMPACT IONIZATION AND LOCK-ON IN GaAs

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  1. MONTE CARLOSIMULATIONS OF IMPACT IONIZATION AND LOCK-ON IN GaAs Samsoo Kang and Charles W. Myles Department of Physics Texas Tech University Harold P. Hjalmarson Sandia National Laboratories SK and CWM supported in part by Texas Advanced Research Program Grant No. 003644-047 HPH Supported by DOE Contract DE-ACOR-94AL85000

  2. Motivation Understanding GaAs Photoconductive Switch Behavior Impact Ionization Initiation of Lock-On

  3. Lock-On • Characterized by a persistent or “locked-on” electric field after laser turn off. • High conductivity state. • Always accompanied by current filaments. • Lock-On field much lower than breakdown field for GaAs.

  4. Collective Impact Ionization Theory(Hjalmarson, et al.1,2) • Basic ideas: • Above a critical carrier density, carrier-carrier scattering becomes very important. • At high carrier densities, this increases the impact ionization efficiency of hot carriers. • This leads to the formation of current filaments and to the initiation of Lock-On.

  5. Present Work • Ensemble Monte Carlo simulations of impact ionization with and without carrier-carrier scattering4. Several carrier densities. (Enhanced carrier-carrier scattering). • Empirical pseudopotential bandstructures5. (One valence and two conduction bands.) • Phonon and carrier-carrier scattering included in full quantum mechanical formulations4.

  6. Ensemble Monte Carlo • Generate a look up table for carrier-carrier scattering and impact ionization. • Initial distribution of particles using random numbers. • Search for carrier-carrier scatterings and impact ionization events. Update distribution function. • Search for phonon scatterings. Update distribution function.

  7. Phonon Scattering Rate Total phonon scattering rate

  8. Distribution Function Distribution function without carrier-carrier scattering at four different electric fields.

  9. Distribution function for 50 particles with (dashed curve) and without (solid curve) carrier-carrier scattering. F = 100 kV/cm.

  10. Distribution function for F = 300 kV/cm without (solid) and with carrier-carrier scattering for 50 (dotted) and 500 (dashed) particles.

  11. Impact Ionization Coefficient (F) = probability per unit length that a carrier will impact ionize at the field F. (F) = rii(F)/vs rii(F) = impact ionization rate at field F (computed by Monte Carlo). vs = carrier velocity

  12. Impact ionization coefficient without (dotted curve) and with (solid curve) carrier-carrier scattering (50 particles). Comparison with other calculations (without CC scattering6,7).

  13. Summary • Phonon scattering rate: Similar to those of previous workers. • Distribution function: Strongly affected by carrier-carrier scattering & by carrier density. • Impact ionization coefficient 1. Without carrier-carrier scattering: Similar to that of other workers. 2. With carrier-carrier scattering: Strongly dependent on carrier density. Enhanced by orders of magnitude.

  14. Conclusions Carrier-carrier scattering: • Has a significant effect on the distribution function at all electric fields (more carriers shifted to higher energies). • Increases the efficiency of impact ionization at high carrier densities. Impact ionization coefficient is increased by orders of magnitude.

  15. Conclusion Monte Carlo simulations have confirmed the basic ideas of Collective Impact Ionization Theory.

  16. References 1. H. Hjalmarson, F. Zutavern, G. Loubriel, A. Baca, K. Khachaturyan, and D. Wake, Sandia Report SNRL93-3972 (1996). 2. H. Hjalmarson, F. Zutavern, G. Loubriel, and D. Wake, to be published. See also H. Hjalmarson et al., Paper O8C, this conference. (Talk is Tuesday at 10:30 A.M.) 3. G. Loubriel, F. Zutavern, H. Hjalmarson, and M. O’Malley, Proc. 7th IEEE Pulsed Power Conf., Monterey, CA, 1989, p. 45. 4. S. Kang, PhD Thesis, Texas Tech U., 1998. 5. M. Cohen and T. Bergstresser, Phys. Rev.141, 789 (1969). 6. K. Brennan and K. Hess, Solid State Elect. 27, 347 (1984). 7. H. Jung, K. Taniguchi, and C. Hamaguchi, J. Appl. Phys.79, 2473 (1996).

  17. Please also see related papers: 1. Paper Number PA101 “Steady State Properties of Lock-On Current Filaments in GaAs”, by K. Kambour et al., this poster session. 2. Paper Number O8C “Collective Impact Ionization Theory of Lock-On”, by H. Hjalmarson et al., Tues., June 29, 1999, 10:30-10:45 AM

  18. Please also see related papers: 1. Paper Number PA102 “Monte Carlo Simulations of Impact Ionization and Lock-On in GaAs,” by S. Kang et al., this poster session. 2. Paper Number O8C “Collective Impact Ionization Theory of Lock-On”, by H. Hjalmarson et al., Tues., June 29, 1999, 10:30-10:45 AM

  19. PAPER PA102

  20. PAPER PA101

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