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NEET Physics Semiconducting Devices NEET PYQ-Semiconducting Devices

  • question_answer
    Pure Si at 500 K has equal number of electron \[({{n}_{e}})\]and hole \[({{n}_{h}})\] concentrations of \[1.5\times {{10}^{16}}{{m}^{-3}}\]. Doping by indium increases \[{{n}_{h}}\] to\[4.5\times {{10}^{22}}{{m}^{-3}}\]. The doped semiconductor is of                                                                                    [AIPMT (M) 2011]

    A)  p-type   with   electron   concentration \[{{n}_{e}}=5\times {{10}^{22}}\,{{m}^{-3}}\]

    B)  p-type   with   electron   concentration \[{{n}_{e}}=2.5\times {{10}^{10}}\,{{m}^{-3}}\]

    C)  n-type   with   electron   concentration \[{{n}_{e}}=2.5\times {{10}^{23}}\,{{m}^{-3}}\]

    D)  p-type having electron  concentration \[{{n}_{e}}=5\times {{10}^{9}}\,{{m}^{-3}}\]

    Correct Answer: D

    Solution :

    \[n_{i}^{2}={{n}_{e}}{{n}_{h}}\]
                \[{{n}_{e}}=\frac{{{({{n}_{i}})}^{2}}}{{{n}_{h}}}\]
    \[{{n}_{e}}=\frac{{{(1.5\times {{10}^{16}})}^{2}}}{(4.5\times {{10}^{22}})}\]
    \[{{n}_{e}}=5\times {{10}^{9}}{{m}^{-3}}\]
                So, \[{{n}_{h}}>>{{n}_{e}}\] semiconductor is p-type.


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