The number desnity of donor atoms which have to be added to an intrinsic germanium semiconductor to produce an n-type semiconductor of conductivity `5 ohm^(-1) cm^(-1)` is `axx10^(15)cm^(-3)`. Given that the mobility of electron in n-type Ge is `3900 cm^(2)//Vs`, Neglect the contribution of holes to conductivity. What is the integer value of a?

The number desnity of donor atoms which have to be added to an intrins

1.	The number desnity of donor atoms which have to be added to an intrinsic germanium semiconductor to produce an n-type semiconductor of conductivity `5 ohm^(-1) cm^(-1)` is `axx10^(15)cm^(-3)`. Given that the mobility of electron in n-type Ge is `3900 cm^(2)//Vs`, Neglect the contribution of holes to conductivity. What is the integer value of a?
Answer» Here, `sigma=5Omega^(-1)cm^(-1), mu_(e)=3900 cm^(2)//Vs, n_(e)=?` We know that, `sigma=1/rho=e n_(e) mu_(e)` or `n_(e)=sigma/(emu_(e))=5/((1.6xx10^(-19))xx3900)~=8xx10^(15) cm^(-3)`. Since, one donor atom provides one free electron to the germanium semiconductor, therefore, number bensity of donor atoms `=8xx10^(15) cm^(-3)`