Silicon, especially in its crystalline form, has certain chemical properties that allow its atoms to attach to one another easily. These atoms form tight bonds that do not easily lose or gain electrons. In order to create a silicon semiconductor, we can introduce impurities, meaning other atoms are mixed in with the silicon atoms. The process of adding impurities is called "doping." When pure silicon is doped with phosphorous, for example, it creates N-type silicon (negative), which means it loses extra free electrons when hit with energy (such as sunlight). On the other hand, when pure silicon is doped with boron, it creates P-type silicon (positive), which offers free openings ready to attract electrons. An electrical current can be created when energy is applied to silicon, causing these electrons, or free carriers, break and build atomic bonds.
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