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Gain and Bandwidth in Semiconductor Photodetectors

This study delves into methods to boost gain and bandwidth in semiconductor photodetectors, covering key factors such as photoconductivity, photoconductive gain, and photovoltaic detection principles. The text explores the intricacies of detection mechanisms, transit times, diffusion, drift velocity, and carrier conductivities in silicon material. Additionally, it delves into the parameters influencing optimum performance, like absorption lengths, junction capacitance, and electric field calculations for P-I-N diodes and semiconductor junctions. Understanding these concepts can aid in improving the efficiency and effectiveness of photodetection technologies.

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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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