Electrical conductivity of an intrinsic semiconductor On which factor does the electrical conductivity of an intrinsic semiconductor depend? It doesn't have an excess of charge carriers in fact, does it? 
 A: Conductivity of intrinsic semiconductor is due to their own internal charge carriers. The bonding between between two electrons of two neighboring atoms is covalent, therefor at NTP, there is no free charge carrier for conduction. When it is heated, some covalent bonds break due to heat and thus some electron get free for conduction. As soon as one electron gets free, there is a deficiency of electrons at its preceding position which acts as a positive charge or a hole, The number of holes is equal to number of electrons. At normal temperature, only $1$ ou of $10^9$ bonds break and therefore, conductivity is very low about few milli amps.
A: Electron and hole generation takes place when a bond breaks. 
Average energy of these particles under thermal equilibrium is $KT=0.026\,eV$.So when a semiconductor block sits at room temperature its average energy is KT. But to break a Si-Si bond we need 1.1eV of energy. So if we want to break a silicon bond we have to take* n* particles to converge at Si=Si bond so that it generates $1.1\,eV$  and breaks the bond.
$$1.1\,eV=n \cdot KT \Rightarrow n=42 (Particles)$$
So we need 42 particles to break a bond. Obviously the probability($p^{42}$) of this happening is very small. This explains why why a very small fraction of silicon atom actually contribute to e-h pair at $300k$. As the temperature rise $KT$ increases and hence probability of particle converging to a single point increases. 
In simpler terms we need electrons and holes(for semiconductors) for conductivity. EHP generation takes place when energy is equal to $1.1\,eV$(for Si). Probability changes as we raise the temperature. So temperature is the main factor for conductivity in an intrinsic semiconductor. 
