What is doping process

The 5-valent dopant has an outer electron more than the silicon atoms. Four outer electrons combine with ever one silicon atom, while the fifth electron is free to move and serves as charge carrier. This free electron requires much less energy to be lifted from the valence band into the conduction band, than the electrons which cause the intrinsic conductivity of silicon.

The dopant, which emits an electron, is known as an electron donor donare, lat. The dopants are positively charged by the loss of negative charge carriers and are built into the lattice, only the negative electrons can move. Doped semimetals whose conductivity is based on free negative electrons are n-type or n-doped. Due to the higher number of free electrons those are also named as majority charge carriers, while free mobile holes are named as the minority charge carriers.

Arsenic is used as an alternative to phosphorus, because its diffusion coefficient is lower. Aluminum, indium, gallium, and boron are trivalent impurities. A trivalent acceptor impurity element can also be used to dope germanium. In this case, the impurity is 1 electron short of the required amount of electrons needed to establish covalent bonds with 4 neighboring atoms.

Thus, in a single covalent bond, there will be only 1 electron instead of 2. This arrangement leaves a hole in that covalent bond. Figure illustrates this theory by showing what happens when germanium is doped with an indium In atom.

Notice, the indium atom in the figure is 1 electron short of the required amount of electrons needed to form covalent bonds with 4 neighboring atoms and, therefore, creates a hole in the structure. This creates a void in lattice which we call it has hole.

Since the electron is deficient, the hole readily accepts an electron, this makes it a P-type Positive type extrinsic semiconductor. As you can see in the image above Figure : P-type , we have popped in boron trivalent element in silicon lattice.

This has created a hole making the semiconductor a P-type material. The case is no different with Germanium. It behaves the same as silicon; however, some properties differ which makes germanium based devices better in certain applications, while silicon based devices are used in other applications. From Wikibooks, open books for an open world. How Doping Works [ edit edit source ]. Expressed in a different form, the ratio of minority to majority carriers is less than one person to the entire population of the planet.

Minority carriers are created either thermally or by incident photons. N -type semiconductor. These are called " n -type" since the majority carriers are N egatively charged electrons. P -type semiconductor. These are called " p -type" since the majority carriers are P ositively charged holes. Skip to main content.