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MindMap Gallery Chapter 2 Impurity Energy Levels and Defect Energy Levels in Semiconductors
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Chapter 2 Impurity Energy Levels and Defect Energy Levels in Semiconductors
This is a mind map about the impurity energy levels and defect energy levels in semiconductors in Chapter 2. In an ideal crystal lattice, atoms are arranged strictly periodically, and the electronic energy states form a series of energy bands (allowed bands), and the energy bands There are no electronic states in the forbidden band between.
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- One Hundred Years of Solitude Character Relationship Chart
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Chapter 2 Impurity Energy Levels and Defect Energy Levels in Semiconductors
- One Hundred Years of Solitude Character Relationship Chart
One Hundred Years of Solitude is the masterpiece of Gabriel Garcia Marquez. Reading this book begins with making sense of the characters' relationships, which are centered on the Buendía family and tells the story of the family's prosperity and decline, internal relationships and political struggles, self-mixing and rebirth over the course of a hundred years.
- One Hundred Years of Solitude Character Relationship Chart
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Project management is the process of applying specialized knowledge, skills, tools, and methods to project activities so that the project can achieve or exceed the set needs and expectations within the constraints of limited resources. This diagram provides a comprehensive overview of the 8 components of the project management process and can be used as a generic template for direct application.
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Chapter two Impurity energy levels and defect energy levels in semiconductors
Overview
The difference between real crystals and ideal crystals with defects
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
Point defects (vacancies, interstitial atoms, antistructural defects)
Line defects (dislocations: edge dislocations and screw dislocations)
Surface defects (stacking faults, grain boundaries)
Generation of impurity and defect energy levels
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.
Impurity energy levels in silicon and germanium crystals
According to the way impurities enter the semiconductor
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
According to the conductivity type of semiconductor affected by impurities
donor impurity
Donor impurities release electrons, i.e. provide electrons to the guide band
When the donor is in the ionized state, it becomes a positively charged center
Group V elements can release electrons when ionized in silicon and germanium to produce conductive electrons and form positive centers. Such impurities are called donor impurities or n-type impurities.
Donor ionization energy ΔED Donor energy level - The energy state of an electron bound by a donor impurity, recorded as ED. Usually at room temperature, impurities can be fully ionized. The electron concentration is equal to the impurity concentration. n-type semiconductor: A semiconductor that mainly relies on conduction band electrons to conduct electricity.
acceptor impurity
The process by which acceptor impurities release holes, that is, provide holes to the valence band.
When the acceptor impurity is in the ionized state, it becomes a negatively charged center
Group III elements can accept electrons when ionized in silicon and germanium to generate conductive holes and form negative centers. Such impurities are called acceptor impurities or p-type impurities.
The acceptor ionization energy is ΔEA Acceptor energy level - the energy state of a hole bound by an acceptor impurity, recorded as EA. At room temperature, the acceptor impurity is completely ionized, and the hole concentration is equal to the acceptor impurity concentration. p-type semiconductor: A semiconductor that mainly relies on holes in the valence band to conduct electricity.
Compensation effect of impurities
Def: When both the donor impurity ND and the acceptor impurity NA exist in the semiconductor, the donor and acceptor will cancel each other out.
When ND>>NA: electrons fill the acceptor energy level EA, all remaining electrons on the donor energy level are excited to the conduction band, the electron concentration in the conduction band is n = ND — NA, and the semiconductor is N-type When NA>>ND, the hole concentration in the valence band is p = NA — ND, and the semiconductor is P-type.
When both donor and acceptor impurities exist in a semiconductor, whether the semiconductor is N-type or P-type is determined by the concentration difference of the impurities. The net impurity concentration in a semiconductor is called the effective impurity concentration (effective donor concentration; effective acceptor concentration).
When NA is approximately equal to ND, the semiconductor is highly compensated by impurities.
Using the compensation effect of impurities to form different conductivity types in different areas of the semiconductor, various devices can be made.
deep level impurities
Typical representative Au
Features
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.
Comperation between deep&shallow
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.
It has a strong recombination effect on carriers (called a recombination center, such as Au) - affecting the working speed of the device.
Shallow energy level impurities - provide conductive carriers to semiconductor materials and affect the conductivity type of semiconductors.
Shallow donor impurities provide electrons - N-type semiconductor; Shallow acceptor impurities provide holes - P-type semiconductor.
Impurity energy levels in II-V compounds
isoelectronic impurities
Impurity atoms often replace host atoms with similar electronegativities or similar atomic radii.
isoelectron trap
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.
impurity bisexuality
Doping group IVA elements such as silicon into III-V compound semiconductors may play both a donor and an acceptor role.
Defects, dislocation energy levels
point defect
Frenkel defect - vacancies and interstitial atoms appear in pairs;
Schottky defects - defects that only form vacancies in the crystal without interstitial atoms
Dislocation
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.
other
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.