Question

A doped semiconductor has impurity levels `40 me V` below the conductor band. Is the material n-type or p-type? In a thermal collision, an amount kT of energy is given to the extra electron loosely bound to the impurity ion and this electron is just able to jump into the conduction band. Calculate the temperature T. Given `k=8.62xx10^(-5) eV//K`.

Answer 1

Since energy gap between impurity levels and conduction band `(=40meV)`, is much smaller than the energy gap of pure semiconductor between valeance band and conduction band `(~~1 eV)`, hence the impurity levels are donor levels and impurity added has valence five. Thus the doped semiconductor is of n-type
or `T=(40meV)/k=(40xx10^(-3)eV)/(8.62xx10^(-5)eV//K)=464K`