Several semiconductor are shown. Semiconductors are usually Silicon, or Germanium based, but can be Zincite(ZnO*MgO), Silicon Carbide (SiC) or other. These materials can act as either conductors or insulators and usually attribute this dual nature to a tiny but necessary doping of a slightly different material, Positive doping leaves holes in a crystal lattice, eg crystalline Silicon doped with Boron, has a very tiny percentage of corners with 3 instead of 4 bonds, think of these corners as wanting to hold a free electron. Crystalline Silicon doped with Phosphorous has a very tiny percentage of corners with 5 instead of 4 bonds, think of these corners as wanting to donate a free electron. Without any defects the Crystalline Silicon would be a really good insulator.