Select Chapter Topics:

1. | The resistivity of a semiconductor increases with an increase in temperature. |

2. | Substances with an energy gap of the order of \(10\) eV are insulators. |

3. | In conductors, the valence and conduction bands may overlap. |

4. | The conductivity of a semiconductor increases with an increase in temperature. |

Subtopic: Â Energy Band theory |

Â 78%

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AIPMT - 2005

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Carbon, Silicon, and Germanium atoms have four valence electrons each. Their valence and conduction bands are separated by energy band gaps represented by ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}},{}_{}$ ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Si}}$, and ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Ge}}$ respectively. Which one of the following relationships is true in their case?

1. ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}}<{\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Ge}}$

2. ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}}>{\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Si}}$

3. ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}}={\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Si}}$

4. ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}}<{\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Si}}$

Subtopic: Â Energy Band theory |

Â 77%

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AIPMT - 2005

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\(\mathrm{C}\), \(\mathrm{Si}\), and \(\mathrm{Ge}\) have the same lattice structure. Why is the \(\mathrm{C}\) insulator?

1. | because ionization energy for \(\mathrm{C}\) is the least in comparison to \(\mathrm{Si}\) and \(\mathrm{Ge}\). |

2. | because ionization energy for \(\mathrm{C}\) is highest in comparison to \(\mathrm{Si}\) and \(\mathrm{Ge}\). |

3. | the number of free electrons for conduction in \(\mathrm{Ge}\) and \(\mathrm{Si}\) is significant but negligibly small for \(\mathrm{C}\). |

4. | both (2) and (3). |

Subtopic: Â Energy Band theory |

Â 73%

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Suppose a pure \(\mathrm{Si}\) crystal has \(5\times10^{28}~\text{atoms m}^{-3}\). It is doped by a \(1\) ppm concentration of pentavalent \(\mathrm{As}\). The number of electrons and holes are, respectively:

(Given: \(n_i=1.5\times10^{16}~\text{m}^{-3}\))

(Given: \(n_i=1.5\times10^{16}~\text{m}^{-3}\))

1. | \(5\times10^{22}~\text{m}^{-3}, 4.5\times10^{9}~\text{m}^{-3}\) |

2. | \(4.5\times10^{9}~\text{m}^{-3}, 5\times 10^{22}~\text{m}^{-3}\) |

3. | \(5\times10^{22}~\text{m}^{-3}, 5\times10^{22}~\text{m}^{-3}\) |

4. | \(4.5\times10^{9}~\text{m}^{-3}, 4.5\times 10^{9}~\text{m}^{-3}\) |

Subtopic: Â Types of Semiconductors |

Â 58%

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Why can't we take one slab of p-type semiconductor and physically join it to another slab of n-type semiconductor to get a p-n junction?

1. | the diffusion of majority charge carriers will not occur. |

2. | the junction will behave as a discontinuity for the flowing charge carriers. |

3. | the junction will behave as a continuity for the flowing charge carriers. |

4. | both (1) and (2). |

Subtopic: Â PN junction |

Â 77%

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The \((V\text-I)\) characteristic of a silicon diode is shown in the figure. The resistance of the diode at \(V_D=-10\) V is:${\mathrm{}}_{}$

1. \(1\times10^7~\Omega~\)

2. \(2\times10^7~\Omega~\)

3. \(3\times10^7~\Omega~\)

4. \(4\times10^7~\Omega~\)$\mathrm{}$

Subtopic: Â PN junction |

Â 80%

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Pure Si at \(500~\text{K}\) has an equal number of electron \((n_e)\) and hole \((n_h)\) concentrations of \(1.5\times10^{16}~\text{m}^{-3}\). Doping by indium increases \(n_h\) to \(4.5\times10^{22}~\text{m}^{-3}\). The doped semiconductor is of:

1. | \(p\)-type with electron concentration \(n_e=5\times10^9~\text{m}^{-3}\). |

2. | \(n\)-type with electron concentration \(n_e=5\times10^{22}~\text{m}^{-3}\). |

3. | \(p\)-type with electron concentration \(n_e=2.5\times10^{10}~\text{m}^{-3}\). |

4. | \(n\)-type with electron concentration \(n_e=2.5\times10^{23}~\text{m}^{-3}\). |

Subtopic: Â Types of Semiconductors |

Â 76%

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AIPMT - 2011

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Let \(n_{p}\) and \(n_{e}\) be the number of holes and conduction electrons in an intrinsic semiconductor. Then:

1. \(n_{p}> n_{e}\)

2. \(n_{p}= n_{e}\)

3. \(n_{p}< n_{e}\)

4. \(n_{p}\neq n_{e}\)

Subtopic: Â Types of Semiconductors |

Â 86%

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A \(\mathrm{p}\text-\)type semiconductor is:

1. | positively charged |

2. | negatively charged |

3. | uncharged |

4. | uncharged at \(0~\text{K}\) but charged at higher temperatures |

Subtopic: Â Types of Semiconductors |

Â 61%

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When an impurity is doped into an intrinsic semiconductor, the conductivity of the semiconductor,

1. increases

2. decreases

3. remains the same

4. becomes zero

Subtopic: Â Types of Semiconductors |

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