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unit 3

Crystal structure of semiconductors

boron

dopants

Silicon and germanium

gallium

Semiconductors are made out of such crystals, usually silicon crystals. Here, each circle represents a silicon atom, and the lines between the atoms represent the shared electrons. Each of the four valence electrons in each silicon atom is shared with one neighboring silicon atom.

The atomic number of silicon is 14 i.e. 14 protons. The number of protons in the nucleus of an atom is called atomic number. Silicon atom has 14 electrons (two electrons in first orbit, eight electrons in second orbit and 4 electrons in the outermost orbit).

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

The crystal structure of gallium is orthorhombic. Natural gallium consists of a mixture of two stable isotopes: gallium-69 (60.4 percent) and gallium-71 (39.6 percent).

The nucleus consists of 5 protons (red) and 6 neutrons (orange). Five electrons (white) occupy available electron shells (rings).

anatomic structure

phosphorus

Phosphorus atoms have 15 electrons and the electronic shell structure is [2, 8, 5] with Atomic Term Symbol (Quantum Numbers)

carbon

For carbon, the atomic number is 6, and the atomic mass number is 12 (6 protons plus 6 neutrons). Adding the two neutrons changes our atom. However, because the number of protons are the same, it is still carbon but now it is an isotope of carbon.

Semiconductors Type N and P.

In a p-type semiconductor, the majority carriers are holes, and the minority carriers are electrons. In the n-type semiconductor, electrons are majority carriers, and holes are minority carriers. ... In an n-type semiconductor, the donor energy level is close to the conduction band and away from the valence band.

When voltage is applied in the forward direction of the p-n junction. When voltage is applied to the p-n junction so that p becomes plus, the holes and the electrons can be moved toward the interface. When holes and electrons meet at the interface (junction), the electrons jump into holes and both are eliminated.

behavior of the PN semiconductor junction