JEE Main & Advanced Physics Semiconducting Devices Question Bank Self Evaluation Test - Semiconductor Electronics: Materials, Devices and Simple Circuits

  • question_answer
    Suppose a 'n'-type wafer is creatd by doping \[Si\]crystal having \[5\times {{10}^{28}}atoms/{{m}^{3}}\] with 1 ppm concentration of As. On the surface 200 ppm Boron is added to create ?P' region in this wafer. Considering \[{{n}_{i}}=1.5\times {{10}^{6}}\,{{m}^{-3}}\] calculate the density of the minority charge carriers in the p regions.    

    A)             \[2.25\times {{10}^{7}}/{{m}^{3}}\]

    B)  \[1.12\times {{10}^{3}}/{{m}^{3}}\]

    C)  \[3.11\times {{10}^{6}}/{{m}^{3}}\]

    D)  \[2.11\times {{10}^{5}}/{{m}^{3}}\]

    Correct Answer: A

    Solution :

    [a] In 'n' region; number of \[{{e}^{-}}\] is due to As: \[{{n}_{e}}={{N}_{D}}=1\times {{10}^{-6}}\times 5\times {{10}^{28}}atoms/{{m}^{3}}\] \[{{n}_{e}}=5\times {{10}^{22}}/{{m}^{3}}\]  The minority carriers (hole) is \[{{n}_{h}}=\frac{n_{i}^{2}}{{{n}_{e}}}=\frac{{{(1.5\times {{10}^{16}})}^{2}}}{5\times {{10}^{22}}}=\frac{2.25\times {{10}^{32}}}{5\times {{10}^{22}}}\] \[{{n}_{h}}=0.45\times 10/{{m}^{3}}\] Similarly, when Boron is implanted a ?p? type is created with holes \[{{n}_{h}}={{N}_{A}}=200\times {{10}^{-6}}\times 5\times {{10}^{28}}=1\times {{10}^{25}}/{{m}^{3}}\] This is far greater than \[{{e}^{-}}\] that existed in 'n' type wafer on which Boron was diffused. Therefore, minority carriers in created 'p' region \[{{n}_{e}}=\frac{n_{i}^{2}}{{{n}_{h}}}=\frac{2.25\times {{10}^{32}}}{1\times {{10}^{25}}}=2.25\times {{10}^{7}}/{{m}^{3}}\]


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