In an intrinsic semiconductor, the energy gap Eg is 1.2eV. Its hole mobility is much smaller than electron mobility and independent of temperature. What is the ratio between conductivity at 600K and that at 300K? Assume that the temperature dependence of intrinsic carrier concentration ni is given by


where n0 is a constant.

Given,

Energy gap (Eg) = 1.2eV


The temperature dependence of intrinsic carrier concentration is given as



Where T is the temperature


Eg is the forbidden energy gap


KB is the Boltzmann’s constant (8.62 × 10-5 eV/K)


no is a constant.


At temperature T1 = 600K,


……….(1)


At temperature T2 = 300K,


…..(2)


Dividing eqn. (1) by eqn. (2), we get



⇒


⇒


⇒


⇒


So,


Hence, the ratio of conductivity at 600K to that at 300K is 1.09 × 105.


NOTE: 1. Eg is the forbidden energy gap which is the energy gap between the valence band and conduction bands.


2. Intrinsic semiconductors are pure semiconductors with fewer conductivities. Trivalent and pentavalent impurities are added to intrinsic semiconductors to form p-type and n-type semiconductors respectively. This process is called doping.


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