N-Type Wafers

N-Type Wafer

Pure silicon is not conductive and therefore is rarely used as semiconductors. In order to make pure silicon into practically usable semiconductors, a controlled quantity of impurities must be added. The addition of impurity will change the conductivity and make the silicon into a semiconductor. The process of adding an impurity to an intrinsic or pure material is called doping and the impurity is called a dopant. After doping, an intrinsic material becomes an extrinsic material. Practically only after doping will the materials become usable.

When an impurity atom is added to silicon without modifying the crystal structure, an N-type material is produced. In some atoms, electrons have five electrons in their valence band such as phosphorus (P), arsenic (As) and antimony (Sb). Doping of silicon with either impurity must not change the crystal structure or the bonding process. The extra electron of impurity atom does not take part in a covalent bonding, so it’s free to move around. It takes only a very small quantity of the impurity to create enough free electrons to allow an electric current to flow through the silicon. N-type silicon is a good conductor. Electrons have a negative charge, hence the name N-type. The following figure shows alteration of silicon crystal with the addition of an impurity atom.

Due to the conductive property of N-type silicon, it is widely used in a lot of applications such as power devices, diodes, and transistors, etc.