Extrinsic Semiconductors

Q. If $N_P$ and $N_e$ be the numbers of holes and conduction electrons in an extrinsic semiconductor, then

1. $N_P>N_e$
2. $N_P=N_e$
3. $N_P<N_e$
4. $N_P>N_e$ or $N_P<N_e$ depending on the nature of impurity

Q. What is the number density of donor atoms which must be added to a pure germanium semiconductor to produce an N-type semiconductor of conductivity $6.4\times {10}^2{\text{ohm}}^{–1}{\text{m}}^{–1}$ ? The mobility of electrons in N-type germanium is $4\times {10}^{–1}{\text{m}}^2{\text{V}}^{–1}{\text{s}}^{–1}$. Neglect contribution of holes to conductivity.

1. ${10}^{20}{\text{m}}^{-3}$
2. ${10}^{21}{\text{m}}^{-3}$
3. ${10}^{22}{\text{m}}^{-3}$
4. ${10}^{23}{\text{m}}^{-3}$

Q. p-type semiconductor are

1. positively charged
2. produced when boron is added as an impurity
3. produced when phosphorus is added as an impurity to silicon
4. produced when carbon is added as an impurity to germanium.

Q. What is the number density of donor atoms which must be added to a pure germanium semiconductor to produce an N-type semiconductor of conductivity $6.4\times {10}^2{\text{ohm}}^{–1}{\text{m}}^{–1}$ ? The mobility of electrons in N-type germanium is $4\times {10}^{–1}{\text{m}}^2{\text{V}}^{–1}{\text{s}}^{–1}$. Neglect contribution of holes to conductivity.

1. ${10}^{20}{\text{m}}^{-3}$
2. ${10}^{21}{\text{m}}^{-3}$
3. ${10}^{22}{\text{m}}^{-3}$
4. ${10}^{23}{\text{m}}^{-3}$

Q.

The valence of an impurity added to germanium crystal in order to convert it into a P-type semi conductor is ?

1. 6

2. 5

3. 4

4. 3

Q. What is the number density of donor atoms which must be added to a pure germanium semiconductor to produce an N-type semiconductor of conductivity $6.4\times {10}^2{\text{ohm}}^{–1}{\text{m}}^{–1}$ ? The mobility of electrons in N-type germanium is $4\times {10}^{–1}{\text{m}}^2{\text{V}}^{–1}{\text{s}}^{–1}$. Neglect contribution of holes to conductivity.

1. ${10}^{20}{\text{m}}^{-3}$
2. ${10}^{21}{\text{m}}^{-3}$
3. ${10}^{22}{\text{m}}^{-3}$
4. ${10}^{23}{\text{m}}^{-3}$