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VIT Engineering VIT Engineering Solved Paper-2008

  • question_answer
     A \[p-n\] junction has acceptor impurity concentration of \[{{10}^{17}}\]\[c{{m}^{-3}}\]in the \[P\] side and donor impurity concentration of \[{{10}^{16}}c{{m}^{-3}}\]in the \[N\] side. What is the contact potential at the junction? (\[kT=\]thermal energy, intrinsic carrier concentration \[{{n}_{i}}1.4\times {{10}^{10}}c{{m}^{-3}}\])

    A)  \[\text{(}kT/e)\text{ }In\text{ }(4\times {{10}^{12}})\]

    B)  \[\text{(}kT/e)\text{ }In\text{ }(2.5\times {{10}^{23}})\]

    C)  \[(kT/e)\text{ }ln\text{ }({{10}^{23}})\]

    D)  \[(kT/e)\text{ }ln\text{ }({{10}^{9}})\]  

    Correct Answer: A

    Solution :

    Constant potential at the junction \[{{V}_{\text{constant}}}=\frac{kT}{e}\] In \[\left( \frac{{{n}_{a}}{{n}_{d}}}{n_{i}^{2}} \right)\] \[\therefore \] \[{{V}_{\text{constant}}}=\frac{kT}{e}\] In \[\left( \frac{{{10}^{17}}\times {{10}^{16}}}{{{(1.4\times {{10}^{10}})}^{2}}} \right)\] \[\frac{kT}{e}\] In \[(4\times {{10}^{12}})\]


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