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Semiconductors and Semiconductor Devices — Physics STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 SciencePhysicsSemiconductors and Semiconductor Devices5 Marks
Question
When a p-n junction is reverse-biased, the current becomes almost constant at $25\mu\text{A}.$ When it is forwardbiased at 200mV, a current of $75\mu\text{A}$ is obtained. Find the magnitude of diffusion current when the diode is,
  1. Unbiased.
  2. Reverse-biased at 200mV.
  3. Forward-biased at 200mV.
✓

Answer

  1. $\text{i}_1=25\mu\text{A},\text{V}=200\text{mV},\text{i}_2=75\mu\text{A}$
When in unbiased condition drift current = diffusion current
$\therefore$ Diffusion current $=25\mu\text{A}.$
  1. On reverse biasing the diffusion current becomes ‘O’.
  2. On forward biasing the actual current be x.
x - Drift current = Forward biasing current
$\Rightarrow\text{x}-25\mu\text{A}=75\mu\text{A}$
$\Rightarrow\text{x}=(75+25)\mu\text{A}=100\mu\text{A}.$

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