Band Theory of Solids

In a metal, the separation between conduction band and valence band is of the order;

Which of the following is the best conductor of electricity?

The energy band gap of gallium arsenide phosphate is $1.98 e\mathrm{V}$. Calculate the wavelength of electromagnetic radiation emitted (in Angstrom), when electrons and holes combine in this alloy semiconductor directly. (Take Planck's constant $\left(h\right)=6.62\times {10}^{-34 }\mathrm{J} \mathrm{s}$)

The forbidden gap in the energy bands of germanium at room temperature is about 

If the energy of a photon of sodium light $(\mathrm{\lambda }=589 \mathrm{n}\mathrm{m})$ is equal to the bandgap of a semiconductor, calculate the minimum energy required to create hole-electron pair. Take, $h=6.6\times {10}^{-34} \mathrm{J} \mathrm{s}, c=3\times {10}^8 \mathrm{m} {\mathrm{s}}^{-1}$.

The forbidden energy gap between the conduction band and the valence band is not present in

Describe the conduction band and valence band in semiconductors.

Describe the conduction band and valence band in insulators.

Describe the conduction band and valence band in metals.

Carbon, silicon and germanium have four valence electrons each. At room temperature which one of the following statements is most appropriate?

The probability of electrons to be found in the conduction band of an intrinsic semi-conductor at a finite temperature

The conductivity of a semiconductor increases with increase in temperature because the number density of free current carriers increases.

In a conductor, the energy gap between conduction bands and valence bands is

For an insulator, the energy gap between the valency band and the conduction band should be less than 3 electron volts.

Explain the movement of charge carriers in conduction band and valency band in an insulator.

In insulators, the valence and conduction bands are separated by a small energy gap. 
 

The energy band occupied by the valence electrons is called a valence band whereas the energy band formed by the energy levels higher than those of valence orbitals is called a conduction band.

If the energy of a photon of sodium light $(\mathrm{\lambda }=589 \mathrm{n}\mathrm{m})$ is equal to the bandgap of a semiconductor, calculate the minimum energy required to create hole-electron pair. Take, $h=6.6\times {10}^{-34} \mathrm{J} \mathrm{s}, c=3\times {10}^8 \mathrm{m} {\mathrm{s}}^{-1}$.

In a photodiode, the conductivity increases when the material is exposed to light. It is found that conductivity changes only if the wavelength is less than $600 \mathrm{n}\mathrm{m}.$ What is the bandgap?

A p-n photodiode is fabricated from a semiconductor with band gap of $2.8 \mathrm{eV}$. Can it detect a wavelength of $6000 \mathrm{nm}$?