Another, slightly thicker, layer of doped silicon is placed underneath the phosphorous-doped silicon layer. This layer is doped with boron (atomic number 5.) Boron atoms have fewer valence electrons than silicon.
(1) What type of semiconductor has the boron-doped silicon become, n or p?
(2) At the junction of the phosphorous-doped silicon and the boron-doped silicon, what will any free electrons do?
(3) What effect will this have on the phosphorous atoms? And on the upper layer?
(4) What effect will this have on the boron atoms? And on the lower layer?
(5) Suggest why the region immediately on either side of the junction between the two layers is called a 'depletion zone'.
(6) Has the upper layer become relatively positively charged or relatively negatively charged?
(7) Has the lower layer become relatively positively charged or relatively negatively charged?
(8) In which direction is there an electric field in the depletion zone?