Semiconductor Electronics: Materials, Devices & Simple Circuits Test 1

As temperature increases electrons from the valence band go to the conduction band, so conductivity increases hence resistance decreases.

Silicon has a forbidden gap of 1.1 eV at 300 K temperature.
 

It is an N-type semiconductor because the density of electrons is more here.

• The electrons surrounding each atom in a semiconductor are part of a covalent bond. A covalent bond consists of two atoms "sharing" a single electron.
• Each atom forms 4 covalent bonds with the 4 surrounding atoms. Therefore, between each atom and its 4 surrounding atoms, 8 electrons are being shared.

• In the case of insulators, the energy gap is very large while in the case of conductors energy gap is very short.
• This energy gap refers to the energy difference between the valence band and conduction band whereas, in semiconductors, this band gap value is in between that of conductors and insulators.

There are two types of semiconductors: p-type and n-type. Therefore both holes and electrons conduct current respectively.

Electrons in metal behave as gas.

The dielectric constant of a medium K = ∈/∈₀ 
where ∈ is the permittivity of the medium.
For air, ∈ = ∈₀​
⟹ K = 1

Here n = 2.5 * 10¹⁹ / m³  ; e = 1.6 * 10^-19 C, µ_h = 0.17 m²/Volt-sec
σ = ne(µ_e + µ_h) 
σ =  (2.5 * 10¹⁹) * (1.6 * 10^-19) (0.36 + 0.17) = 2.12 S/m

In semiconductors, the forbidden gap between the valence band and conduction band is very small. It has a forbidden gap of about 1 electron volt (eV).