P-type semiconductor

A p-type semiconductor is one of two main types of semiconductors, the other being an n-type semiconductor. The p and n stand for positively-doped and negatively-doped, respectively. When a trivalent impurity (like boron, aluminum etc.) is added to an intrinsic or pure semiconductor (silicon or germanium), it is said to be a p-type semiconductor. Trivalent impurities such as boron (B), gallium (Ga), indium (In), aluminum (Al) etc. are called acceptor impurities. Ordinary semiconductors are made of materials that do not conduct (or carry) an electric current very well but are not highly resistant to doing so either. Metalloids, such as silicon (Si), germanium (Ge), arsenic (As), and a few other elements are commonly used for the main body of semiconductors. Their bulk conductivity falls halfway between that of conductors and insulators and so are called semiconductors. For an electric current to flow, charge carriers have to move through a material. A p-type semiconductor has free holes in its crystal lattice which can move in response to an applied electric field, causing current to flow.

Semiconductors are usually made from a material called silicon. Silicon is a chemical element that has four electrons in its outer layer. To make a type of semiconductor called "p-type," scientists add a small amount of another material, like boron or aluminum. These materials have only three electrons in their outer layer. When they replace some of the silicon atoms, they leave an empty space, or "hole," where a fourth electron would normally be. These holes help electricity move through the semiconductor. 4o

P-type semiconductors are made by adding materials called acceptors. These can take in extra electrons. N-type semiconductors are made by adding materials called donors. Donors give extra electrons. A PN junction, like in a diode, is made by putting P-type and N-type semiconductors together. Electrons move from the N-type side to the P-type side. This movement allows electricity to flow in only one direction.

Manufacture

P-type semiconductors are made by doping the pure semiconductor material. The amount of impurity added is very small compared to the amount of semiconductor. The exact character of the semiconductor can be changed by varying the amount of dopant that is added. In p-type semiconductors the number of holes is much higher than that of thermally generated electrons.

Related pages

• Semiconductor
• N-type semiconductor

Other websites

• The Doping of Semiconductors - Hyperphysics
• PN Junction Theory - Electronics Tutorials