In silicon, the conduction and valence brands lie close in energy, so that when light is absorbed, electrons can be excited from the valence to the conduction band where they can travel freely through the solid.
a. why does pure silicon not produce a measurable current?
b. describe the effect of doping silicon with indium. what type of semiconductor is produced?
c. in building a photovoltaic cell, it does not matter which semiconducting layer (p or n) is on top (i. e. first contact with sunlight). however, it is important that the top layer be thin. why?