We Can Figure This Out.org
Virtual Lab: How Semiconductors and Transistors Work
University of Virginia
             
 
© 2003-Present, John C. Bean
 
When we put such a phosphorus atom into a silicon crystal, the first four of its outer (valence) electrons happily align themselves to form bonds with neighboring silicon atoms.

But the fifth valence electron atom has nothing to bond with (because the whole silicon crystal structure is based on providing four bonding neighbors!).

 
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