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Gain and Bandwidth in Semiconductor Photodetectors

Gain and Bandwidth in Semiconductor Photodetectors. S W McKnight and C A DiMarzio. length=l. Area=A. Photoconductivity. Φ p = photon flux (photon/sec). η = quantum efficiency. Photoconductor Responsivity. Photoconductor Detectivity and Bandwidth. Sample thickness ~ absorption length

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Gain and Bandwidth in Semiconductor Photodetectors

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  1. Gain and Bandwidth in Semiconductor Photodetectors S W McKnight and C A DiMarzio

  2. length=l Area=A Photoconductivity Φp = photon flux (photon/sec) η = quantum efficiency

  3. Photoconductor Responsivity

  4. Photoconductor Detectivity and Bandwidth • Sample thickness ~ absorption length • Photoconductive Gain ~ τn • Bandwidth ~ 1/ τn • Gain/Bandwidth product ~ constant

  5. Photovoltaic Detection Jdiffusion E Jdrift Ec Junction “built-in” voltage Vo Ef Ev - + Depletion Region x

  6. Photovoltaic Detection: Gain and Bandwidth • Transit across depletion region fast (vdrift) • Diffusion to depletion region slow (vdiff < <vthermal) • Highest η if absorption is within depletion region • Bandwidth • Transit time of electrons ~ W / (μ ) • Electrical bandwidth ~ 1/RCj • Cj ~ ε A/d ~ 1/W

  7. Diffusion and Drift Velocity Jdiff = q Dn dn/dx = n q vdiff vdiff = Dn 1/n dn/dx = Dn d/dx [ln(n)] ~ Dn ln(gopτ) / (1/α) < < vthermal = sqrt (kT/m) vdrift = μn

  8. Carrier Conductivity Mass Conductivity mass:

  9. Silicon Conductivity Mass b y a c a z x b

  10. Silicon Conductivity Mass

  11. Thermal vs. Drift Velocity

  12. Carrier Saturation Velocities Electrons Holes

  13. Photovoltaic Sensing Circuit + Vph -

  14. Photoconductive Sensing Circuit Iph - + Vd

  15. Photoconductive Detection E Jdrift Ec Vo+ Vd Ev Ef - + Depletion Region x

  16. Depletion Region Width

  17. Absorption Length for Semiconductor

  18. Junction Capacitance

  19. P-I-N Diode Detector

  20. P-N Junction E + - electrons Ef “holes” x Depletion Region

  21. Abrupt Junction ρ P-side N-side qNd -xop xon x -qNa Charge conservation → q Na xop = q Nd xon

  22. Electric Field Calculation Poisson’s Equation: 1D Junction:

  23. Abrupt Junction P-side N-side -xop xon x

  24. P-I-N Junction E + - electrons Ef Ef “holes” x Depletion Region

  25. P-I-N Junction E Ec electrons Ef “holes” Ev - + x Depletion Region

  26. P-I-N Junction P-side I-region N-side xpo xno x ~ Va/W Depletion width = W

  27. Silicon pin diode • W ~ 1/α ~ 10 μ at λ=600 nm • Ebreakdown ~ 106 V/cm • Maximum reverse bias ~ Ebreakdown/W ~ 1000V

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