·
Diffusion
coefficient tells us how effectively does an impurity atom diffuse through the
silicon wafer.

·
Diffusion
coefficient depends exponentially on temperature

**D = D _{0 }exp(-E_{A }/ kT) **

Where D_{0} is the
frequency factor (in cm^{2}/sec)

E_{A}
is the activation energy in eV

*T* is temperature (in K)

K is
Boltzmann constant in eV/K

**Example: Calculate
the diffusion coefficient for boron at 1100****°****C.**

** **

We know that **D = D _{0
}exp(-E_{A }/ kT)**

D_{0}=10.5 cm^{2}/s

*T* =1100°C=1100 + 273 = 1373 K

E_{A} = 3.69 eV / K

K=8.62X10^{-5} eV/K

D=2.96X10^{-13} cm^{2}/sec