Diffusion current in a circuit containing semiconductor but no electric source

[Eng.]

Please I need help to understand how diffusion current can occur in a circuit that contains an N-type or P-type semiconductor without being connected to an electric souce such as a battery.And how can both drift and diffusion current occur when the circuit is connected to a battery?

 

[Bobbywhy]

Eng. Welcome to Physics Forums!

Have you read this yet?
http://en.wikipedia.org/wiki/Diffusion_current

It seems to contain a clear explanation of what you're asking about.

Cheers,
Bobbywhy

 

[Kholdstare]

Diffusion current will be a transient at the time of making of a p-n junction. You won't be able to measure it then.