Lecture 12 OUTLINE pn Junction Diodes contd Deviations

Deviations from the Ideal I-V R. F. Pierret, Semiconductor Device Fundamentals, Figure 6. 10

Effect of R-G in Depletion Region • The net generation rate is given by

Net Generation in Reverse Bias R. F. Pierret, Semiconductor Device Fundamentals, Figure 6. 15(a)

Net Recombination in Forward Bias R. F. Pierret, Semiconductor Device Fundamentals, Figure 6. 15(b)

High-Level Injection (HLI) Effect • As VA increases, the side of the junction which

Effect of Series Resistance R. F. Pierret, Semiconductor Device Fundamentals, Figure 6. 16 EE

Summary: Deviations from Ideal I-V • At large forward biases (high current densities) D:

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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

Deviations from the Ideal I-V R. F. Pierret, Semiconductor Device Fundamentals, Figure 6. 10 Reverse-Bias Current (linear scale) Ideally, EE 130/230 A Fall 2013 Forward-Bias Current (log scale) Ideally, Lecture 12, Slide 2

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: EE 130/230 A Fall 2013 Lecture 12, Slide 3

Net Generation in Reverse Bias R. F. Pierret, Semiconductor Device Fundamentals, Figure 6. 15(a) • For reverse bias greater than several k. T/q, EE 130/230 A Fall 2013 Lecture 12, Slide 4

Net Recombination in Forward Bias R. F. Pierret, Semiconductor Device Fundamentals, Figure 6. 15(b) • For forward bias: EE 130/230 A Fall 2013 Lecture 12, Slide 5

High-Level Injection (HLI) Effect • As VA increases, the side of the junction which is more lightly doped will eventually reach HLI: nn > nno for a p+n junction or pp > ppo for a pn+ junction Þ significant gradient in majority-carrier profile Majority-carrier diffusion current reduces the diode current from the ideal case. EE 130/230 A Fall 2013 Lecture 12, Slide 6 R. F. Pierret, Semiconductor Device Fundamentals, Figure 6. 17(a)

Effect of Series Resistance R. F. Pierret, Semiconductor Device Fundamentals, Figure 6. 16 EE 130/230 A Fall 2013 Lecture 12, Slide 7

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 EE 130/230 A Fall 2013 Lecture 12, Slide 8 R. F. Pierret, Semiconductor Device Fundamentals, Figure E 6 -9