Question 1.7: Objective: Determine the current in a pn junction diode. Con...

Microelectronics Circuit Analysis and Design

Objective: Determine the current in a pn junction diode.

Consider a pn junction at T = 300 K in which $I_{S} = 10^{−14} A$ and n = 1. Find the diode current for $v_{D} = +0.70 V$ and $v_{D} = -0.70 V$

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For $v_{D} = +0.70 V$ the pn junction is forward-biased and we find

i_{D} = I_{S} \left[e^{\left(\frac{v_{D}}{V_{T}} \right) }  –   1 \right] = (10^{-14}) \left[e^{\left(\frac{+ 0.70}{0.026} \right)}  –  1 \right] ⇒ 4.93  mA

For $v_{D} = – 0.70 V$ the pn junction is reverse-biased and we find

i_{D} = I_{S} \left[e^{\left(\frac{v_{D}}{V_{T}} \right)}  –   1 \right] = (10^{-14}) \left[e^{\left(\frac{- 0.70}{0.026} \right) }  –  1\right] ≅ –  10^{-14}   A

Comment: Although $I_{S}$ is quite small, even a relatively small value of forward-bias voltage can induce a moderate junction current. With a reverse-bias voltage applied, the junction current is virtually zero

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