For those who like to see drawings, have a look at semiconductor 101 presentation from Freescale.
N and P channel are well imaged, as well as the other conponents of a semiconductor, like a substrate and much much more
A must for all people, who just like me, didn't knew what is a semiconductior.
Than I really began to to Look Into IT !
Enjoy,
http://cache.freescale.com/files/training/doc/dwf/DWF13_AMF_ENT_T0194.pdf