We just learned about what a Anode and Cathode are.
We learned a while back that semiconductors are chemicals that do not conduct electricity very well.
Some scientists discovered a crazy thing, that if you mix up a semiconductor with another type of chemical,
then when you zap it with electricity it becomes a good conductor!
This is called doping or adding impurities into the semiconductor.
Remember we said silicon was a semiconductor.
The chemical arsenic can be added to silicon for doping.
(from: wikipedia - silicon)
(from: wikipedia - arsenic)