Shortcut Methods

NEET#

• If the conductivity of a semiconductor is $$1 S/m$$ and the mobility of electrons is $${{\mu }_n}= 0.14 m^2 V^{−1} s^{−1}$$ then the number of free electrons per unit volume will be $$8 \times {10^{22}}{m^{−3}}$$

• In an intrinsic semiconductor, the mobility of electrons is $${\mu _e} = 0.05m^2 V^{−1} s^{−1}$$ and that of holes is $${{\mu }_b}= 0.01m^2 V^{−1} s^{−1}$$. If equal number of donor and acceptor atoms with a concentration $$5\times {10^{21}}{m^{−3}}$$ are added, what will be the conductivity of the new semiconductor?

Given,$${\mu _e}=0.05{m^2}V^{−1}{s^{−1}}$$ $$\mu_h=0.01m^2 V^{−1} s^{−1}$$ $$n_d=n_a=5\times {10^{21}}{m^{−3}}$$ $$\sigma =ne\mu_n+pe\mu_p$$ $$=n_de\mu_n+n_de\mu_p \because n_d=n_a$$ $$=n_d(e\mu_n+e\mu_p)$$ $$=n_d(0.05+0.01)\times 1.6\times {10^{−19}}$$ $$n_d=0.06\times 1.6\times {10^{−19}}$$ $$n_d=9.6\times {10^{−21}}{m^{−3}}$$

CBSE Board Exams#

• When a semiconductor is heated, its electrical conductivity increases whereas the conductivity of a metal decreases. Why?

• What is the difference between intrinsic and extrinsic semiconductors?

• The electrical conductivity of a semiconductor material can be increased by:

1. Adding impurities to the material.
2. Increasing the temperature of the material.
3. Both of the above.

• What is the primary application of semiconductors in electronic devices?