Semiconductor diodes

Crystal Structure of Intrinsic Semiconductor: Observe the picture. It is a silicon intrinsic semiconductor material. An outer most shell of an atom is capable of holding eight electrons. It is said to be completely filled and stable, if it consists eight electrons. But outer most shell of an intrinsic semiconductor like silicon has only 4 electrons. Each of these electrons forms a bond with another valance electron of neighbor atoms. These bonds are called covalent bonds. These atoms themselves aligned to form a pattern called crystal.