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The process of adding impurities to the pure semiconductor is called

Drouping

Drooping

Doping

None of these

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Explanation

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To a germanium sample, traces of gallium are added as an impurity. The resultant sample would behave like

A conductor

A P-type semiconductor

An N-type semiconductor

An insulator

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Explanation

(b) Gallium is trivalent impurity.

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Donor type impurity is found in

Trivalent elements

Pentavalent elements

In both the above

None of these

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Explanation

(b) One atom of pentavalent impurity, donates one electron.

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The difference in the variation of resistance with temperature in a metal and a semiconductor arises essentially due to the difference in the

Variation of scattering mechanism with temperature

Crystal structure

Variation of the number of charge carriers with temperature

Type of bond

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Explanation

In a semi-conductor the no. of charge carriers increases with increase in temperature.

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The charge on a hole is equal to the charge of

Zero

Proton

Neutron

Electron

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Explanation

(b) The charge on hole is positive.

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A Ge specimen is doped with Al. The concentration of acceptor atoms is $~ 10^{21} atoms / m^{3}$ . Given that the intrinsic concentration of electron hole pairs is $~ 10^{19} / m^{3}$ , the concentration of electrons in the specimen is

$10^{17} / m^{3}$

$10^{15} / m^{3}$

$10^{4} / m^{3}$

$10^{2} / m^{3}$

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Explanation

(a) $n_{i}^{2} = n_{h} n_{e} \Rightarrow {(10^{19})}^{2} = 10^{21} \times n_{e} \Rightarrow n_{e} = 10^{17} / m^{3}$

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Which of the following has negative temperature coefficient of resistance

Copper

Aluminium

Iron

Germanium

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Explanation

(d) Temperature co-efficient of semiconductor is negative.

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In semiconductors at a room temperature

The valence band is partially empty and the conduction band is partially filled

The valence band is completely filled and the conduction band is partially filled

The valence band is completely filled

The conduction band is completely empty

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Explanation

(a) Copper, Aluminum, Iron are conductors, while Ge is semiconductor.

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Regarding a semiconductor which one of the following is wrong

There are no free electrons at room temperature

There are no free electrons at 0 K

The number of free electrons increases with rise of temperature

The charge carriers are electrons and holes

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Explanation

(a) At room temperature, few bonds breaks and electron hole pair generates inside the semiconductor.

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Which of the following statements is true for an N-type semi-conductor

The donor level lies closely below the bottom of the conduction band

The donor level lies closely above the top of the valence band

The donor level lies at the halfway mark of the forbidden energy gap

None of above

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Explanation

(a) For N-type semiconductor, he donor level lies below the bottom of the conduction band.

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