Tag: solid state

Questions Related to solid state

Which of the following statements is correct about the conduction of electricity in pure crystal of silicon at room temperature?

chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. The conduction is due to electrons present in fully occupied lowest energy states.

  2. The conduction is due to only some electrons capable of leaving the bonds at room temperature.

  3. The conduction is only due to the holes formed from the release of electrons.

  4. The conduction is due to the movement of both the electrons released and holes formed.

Show answer
Correct Option: D
Explanation:

In semiconductor two types of the semiconductor are present. They are an intrinsic and extrinsic semiconductor. A pure silicon crystal is an example of an intrinsic semiconductor. 

The conduction in the intrinsic semiconductor is due to the moving of electrons from valence bond to conduction bond by means of thermal energy. Due to the thermal energy the $Si-Si$ bond breaks and creates electron deficiency which is also called a hole. So, both the holes and electrons released to account for the conduction of electricity.

p type semi conductor is formed when trace amount of impurity is added to silicon. The number of valence electrons in the impurity atom must be:

chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. $3$

  2. $5$

  3. $1$

  4. $2$

Show answer
Correct Option: A
Explanation:

To form a p-type semiconductor, one must add elements from boron family to the silicon atom.

Boron family has 3 valance electrons so, number of valance electrons in the impurity atom must be 3.

Solar cell is constructed by connecting the semi conductors of_____________

chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. n-type and n-tupe

  2. n-type and p-type

  3. p-type and p-type

  4. n-type and n-pn-type

Show answer
Correct Option: A

A semiconductor obtained by doping silicon with elements of group 13 and group is respectively is

chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. P - type

  2. n - type

  3. p type, n type

  4. n type, p type.

Show answer
Correct Option: A

Which of the following acts as a superconductor at $4K$?

chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. $He$

  2. $Cu$

  3. $K$

  4. $Mg$

Show answer
Correct Option: A

Addition of arsenic in small amount to pure germanium will result in the formation of

chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. n-type semiconductor

  2. germanium arsenide

  3. p-type semiconductor

  4. a superconducting alloy

Show answer
Correct Option: A

To get n-type doped semiconductor, impurity to be added to silicon should have number of valence electrons equal to: 

chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. $1$

  2. $2$

  3. $3$

  4. $5$

Show answer
Correct Option: D
Explanation:

To get n-type doped semiconductor, pentavalent impurity should be added to silicon. Example- As in Si.

A solid with high electrical and thermal conductivity is:

chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. $Si$

  2. $Li$

  3. $NaCl$

  4. $Ice$

Show answer
Correct Option: B

If we mix a pentavalent impurity in a crystal lattice of germanium, what type of semiconductor formation will occur? 

chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. p-type

  2. n-type

  3. Both A and B

  4. None of the the above

Show answer
Correct Option: B
Explanation:

Silicon and germanium belong to group 14 of the periodic table and have four valence electrons each. In their crystals each atom forms four covalent bonds with its neighbours. When doped with a group 15 element like P or As, which contains five valence electrons, they occupy some of the lattice sites in silicon or germanium crystal. Four out of five electrons are used in the formation of four covalent bonds with the four neighbouring silicon atoms. The fifth electron is extra and becomes delocalised.These delocalised electrons increase the conductivity of doped silicon(or germanium). Here the increase in conductivity is due to the negatively charged electron, hence silicon doped with electron-rich impurity is called n-type semiconductor.

Select the correct statement.

chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. LiF and MgO are isostructural and also isodimensional, but a crystal of MgO is much harder than one of LiF.

  2. The thermal stability of the isomorphous sulphates of $Ca^{2+}, Sr^{2+}$ and $Ba^{2+}$ w.r.t. decomposition into metal oxide and sulphur trioxide increases in the order $CaSO _4, SrSO _4, BaSO _4$.

  3. Both (a) and (b)

  4. None of above

Show answer
Correct Option: C
Explanation:

LiF and MgO are isostructural and also isodimensional, but a crystal of MgO is much harder than one of LiF because of electronic repulsions in the small sized LiF.
Thermal stability of group 2 sulphates increases down the group. Hence, $CaSO _4 < SrSO _4 < BaSO _4$.