Built in potential of a pin diode?
The PIN diode will have the same barrier for the material; however, it will have a different frequency behavior.  The N and the P regions are highly doped, take a standard band diagram and then stretch it out.  The barrier height will be the the same. 

I have used these devices as attenuators, and the low frequency behavior is identical, but at high frequency, they look much like a resistor.

I believe that there is a write up on them Andy Grove's "Physics and Technology of Semiconductor Devices"; however, I have not seen them described in detail anywhere else.