Diffusion
The process of junction formation i.e. transition from p type to n type or vice versa , is typically accomplished by the process of diffusion.
Diffusion of impurity atoms into silicon crystal takes place at 900 degrees C to 1100 degrees C.
Impurity atoms are introduced onto the surface of a silicon wafer and diffused into the lattice because of their tendency to move from regions of high to low concentration.
Diffusion is used to form base,emitters and resistors in bipolar device technology , to form source and drain regions and to dope polysilicon in MOS device technology.
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