The distance from the surface, x_{j}, at which the
diffused impurity profile intersects the background concentration N_{B},
is called the metallurgical junction x_{j.} The net impurity
concentration at x_{j} is zero.

Fig 4 Formation of a pn junction by diffusion (a) an
example of a p-type Gaussian diffusion into a uniformly doped n-type wafer; (b)
net impurity concentration in the wafer. The metallurgical junction occurs at
the point x=x_{j}, where the net concentration is zero. The material is
converted to p-type to the left of x_{j} and remains n-type to the
right of x_{j}. [1]

**For Gaussian
Distribution**

** **

Impurity concentration at distance x and time t, that is,
N(x,t) is given by

** **

_{}

** **

We know that at junction depth, that is, x=x_{j},
N(x,t)=N_{B, }the background concentration. Therefore, we have,

** _{} **at x= x

The junction depth is given by the following expression.

** **

_{}

**For Complementary
Error Function Distribution**

** **

_{}

At x=x_{j} N(x,t)=N_{B}

_{}

The junction depth is given by the following expression.

_{}