Atoms are not stationary on the grid

There are impurities, that is, there are atoms of other elements in the semiconductor material that are different from the elements that make up the semiconductor material.

Flawed

In an ideal lattice, atoms are arranged in a strictly periodic manner, and the electronic energy states form a series of energy bands (allowed bands), while there are no electronic states in the forbidden bands between the energy bands.

Due to the presence of impurities and defects, the periodic potential field generated by the originally periodically arranged atoms is destroyed, and energy levels are introduced in the forbidden band, allowing electrons to exist in the forbidden band, thereby changing the properties of the semiconductor.

Very small amounts of impurities and defects will have a decisive impact on the physical and chemical properties of semiconductor materials, and also seriously affect the quality of semiconductor devices.

Substitutional impurities: impurity atoms replace lattice atoms and are located at lattice points

Interstitial impurities: Impurity atoms are located in the interstitial positions between lattice atoms

donor impurity

acceptor impurity

Mostly substitutional impurities

The donor energy level generated in the forbidden band of silicon and germanium is far away from the bottom of the conduction band and the acceptor energy level is far away from the top of the valence band, forming a deep energy level, which is called a deep level impurity.

Deep-level impurities can produce multiple ionizations, each ionization corresponding to an energy level. And it can introduce both donor energy level and acceptor energy level.

The generated donor energy level is far from the bottom of the conduction band, and the generated acceptor energy level is far from the top of the valence band. Such energy levels are called deep energy levels; impurities that produce deep (shallow) energy levels are called deep (shallow) energy levels. Impurities.

Shallow energy level impurities - provide conductive carriers to semiconductor materials and affect the conductivity type of semiconductors.

Impurity atoms often replace host atoms with similar electronegativities or similar atomic radii.

Due to differences in electronegativity, isoelectronic impurities in some compound semiconductors can still capture carriers and become charged centers

1. Only when there is a large difference in electronegativity and covalent radius between the incorporated atoms and the host crystal atoms, an isoelectronic trap can be formed. 2. The smaller the atomic number of the same family of elements, the greater the electronegativity and the smaller the covalent radius. If the electronegativity of the impurity is greater than that of the host crystal atoms, electrons will be captured after substitution and become a negative center, otherwise holes will be captured to become a positive center. 3. After the electron trap is charged, it can capture another carrier of the opposite sign through Coulomb force to form bound excitons, which can improve the optical properties of indirect band gap semiconductor materials.

Doping group IVA elements such as silicon into III-V compound semiconductors may play both a donor and an acceptor role.

Frenkel defect - vacancies and interstitial atoms appear in pairs;

Schottky defects - defects that only form vacancies in the crystal without interstitial atoms

At the location of the dislocation, there is an unpaired electron (unsaturated covalent bond): if an electron is gained, it acts as an acceptor; if a valence electron is lost, it acts as a donor.

The lattice around the dislocation is distorted, and the periodic potential field is destroyed, causing changes in the energy band structure, leading to energy band deformation. The band gap width in the lattice stretching area decreases, and the band gap width in the lattice compression area increases.

There are four unpaired electrons around the vacancy in Si and Ge, so the vacancy acts as an acceptor; each interstitial atom has four electrons that can be lost, so the interstitial atom acts as a donor.

When M is an interstitial atom, it is a donor, and when X is an interstitial atom, it is an acceptor. Positive ion vacancies VM are acceptors and negative ion vacancies VX are donors.

In the weakly ionic binary compound AB, the substitution atom AB is the acceptor and BA is the donor, forming an anti-structural defect.