In a photovoltaic cell (a solar cell) a very thin layer of silicon is ‘doped’ with phosphorous. Because silicon has four valence electrons (Si is atomic number 14), all these electrons are locked in place by the atomic bonds that keep the silicon atoms together. Phosphorous is atomic number 15, and so every phosphorous atom bonded to silicon atoms has one electron that is free to move around.
(1) What is meant by the term *doped*?
(2) What type of semiconductor has the silicon doped with phosphorous become, n or p?