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Understanding Deviations in the I-V Characteristics of PN Junction Diodes

This lecture delves into the various deviations from the ideal I-V characteristics of PN junction diodes, focusing on factors such as R-G current, series resistance, and high-level injection. Key concepts explored include net generation and recombination rates, their impact on diode current under reverse and forward bias conditions, and the effects of series resistance in high current scenarios. By analyzing these factors, one gains a deeper understanding of real-world diode behavior, supported by graphical illustrations from R.F. Pierret's "Semiconductor Device Fundamentals".

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Understanding Deviations in the I-V Characteristics of PN Junction Diodes

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  1. Lecture 12 OUTLINE • pn Junction Diodes (cont’d) • Deviations from the ideal I-V • R-G current • series resistance • high-level injection Reading: Pierret 6.2

  2. Deviations from the Ideal I-V R. F. Pierret, Semiconductor Device Fundamentals, Figure 6.10 Reverse-Bias Current (linear scale) Forward-Bias Current (log scale) Ideally, Ideally, EE130/230A Fall 2013 Lecture 12, Slide 2

  3. Effect of R-G in Depletion Region • The net generation rate is given by • R-G in the depletion region contributes an additional component of diode current IR-G: EE130/230A Fall 2013 Lecture 12, Slide 3

  4. Net Generation in Reverse Bias R. F. Pierret, Semiconductor Device Fundamentals, Figure 6.15(a) • For reverse bias greater than several kT/q, EE130/230A Fall 2013 Lecture 12, Slide 4

  5. Net Recombination in Forward Bias R. F. Pierret, Semiconductor Device Fundamentals, Figure 6.15(b) • For forward bias: EE130/230A Fall 2013 Lecture 12, Slide 5

  6. High-Level Injection (HLI) Effect • As VA increases, the side of the junction which is more lightly doped will eventually reach HLI: • significant gradient in majority-carrier profile Majority-carrier diffusion current reduces the diode current from the ideal case. nn > nno for a p+n junction or pp > ppo for a pn+ junction R. F. Pierret, Semiconductor Device Fundamentals, Figure 6.17(a) EE130/230A Fall 2013 Lecture 12, Slide 6

  7. Effect of Series Resistance R. F. Pierret, Semiconductor Device Fundamentals, Figure 6.16 EE130/230A Fall 2013 Lecture 12, Slide 7

  8. Summary: Deviations from Ideal I-V • At large forward biases (high current densities) D: high-level injection E: series resistance limit increases in current with increasing forward bias voltage. B: Excess current under reverse bias is due to net generation in the depletion region. C: Excess current under small forward bias is due to net recombination in the depletion region. A: At large reverse biases (high E-field), large reverse current flows due to avalanching and/or tunneling R. F. Pierret, Semiconductor Device Fundamentals, Figure E6-9 EE130/230A Fall 2013 Lecture 12, Slide 8

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