AIIMS AIIMS Solved Paper-2004

  • question_answer
    A Ge specimen is doped with Al. The concentration   of   acceptor   atoms   is \[\tilde{\ }\,{{10}^{21}}\] atoms/\[{{m}^{3}}\]. Given that the intrinsic concentration  of electron-hole  pairs is \[\tilde{\ }{{10}^{19}}/{{m}^{3}},\] the concentration of electrons in the specimen is:

    A) \[{{10}^{17}}/{{m}^{3}}\]

    B)                       \[{{10}^{15}}/{{m}^{3}}\]             

    C)       \[{{10}^{4}}/{{m}^{3}}\]               

    D)       \[{{10}^{2}}/{{m}^{3}}\]

    Correct Answer: A

    Solution :

                    From law of mass-action \[N_{i}^{2}={{n}_{e}}\times {{n}_{h}}\] where \[{{n}_{i}}\], is concentration of electron-hole pair and \[{{n}_{h}}\] is concentration of acceptor or holes. Given, \[{{n}_{i}}={{10}^{19}}\,per\,{{m}^{3}},\,\,{{n}_{h}}={{10}^{21}}\,per\,{{m}^{3}}\] \[{{({{10}^{19}})}^{2}}={{n}_{e}}\times {{10}^{21}}\] \[\Rightarrow \]   \[{{n}_{e}}=\frac{{{10}^{38}}}{{{10}^{21}}}={{10}^{17}}\,per\,{{m}^{3}}\]


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