What is doping and why we dope semiconductors?
Basically there are two types of semiconductors, intrinsic and extrinsic semiconductors.
Intrinsic materials are those semiconductors that have been carefully refined to reduce the impurities to a very low level—essentially as pure as can be made available through modern technology.
Extrinsic semiconductors are just opposite of intrinsic semiconductor, but they are not full of impurities, but certain impurities are added via process of “doping”.
Doping is the process of adding impurities, it is a specific process of bombarding impurity valence atoms to the semiconductor. And this extent of impurity can be via certain measures, it is a certain industrial process. now, it is not necessary at this topic to tell about it. If you want me to make a post about it, feel free to hit comment section.
N and P type semiconductors
As I said,The characteristics of semiconductor materials can be altered significantly by the addition of certain impurity atoms into the relatively pure semiconductor material.
The n-type is created by introducing those impurity elements that have five valence electrons (pentavalent), such as antimony, arsenic, and phosphorus. the four covalent bonds are still present. There is, however, an additional fifth electron due to the impurity atom, which is unassociated with any particular covalent bond. This remaining electron, loosely bound to its parent (antimony) atom, is relatively free to move within the newly formed n-type material. Since the inserted impurity atom has donated a relatively “free” electron to the structure:
Diffused impurities with five valence electrons are called donor atoms.
It is important to realize that even though a large number of “free” carriers have been established in the n-type material, it is still electrically neutral since ideally the number of positively charged protons in the nuclei is still equal to the number of “free” and orbiting negetively charged electrons in the structure.
The p-type material is formed by doping a pure germanium or silicon crystal with impurity atoms having three valence electrons. The elements most frequently used for this purpose are boron, gallium, and indium.
There is now an insufficient number of electrons to complete the covalent bonds of the newly formed lattice. The resulting vacancy is called a hole and is represented by a small circle or positive sign due to the absence of a negative charge. Since the resulting vacancy will readily accept a “free” electron.
The diffused impurities with three valence electrons are called acceptor atoms.
Majority and Minority Carriers
In the intrinsic state, the number of free electrons in Ge or Si is due only to those few electrons in the valence band that have acquired sufficient energy from thermal or light sources to break the covalent bond or to the few impurities that could not be removed. The vacancies left behind in the covalent bonding structure represent our very limited supply of holes. In an n-type material, the number of holes has not changed significantly from this intrinsic level. The net result, therefore, is that the number of electrons far outweighs the number of holes.
that’s why In an n-type material the electron is called the majority carrier and the hole the minority carrier.
For the p-type material the number of holes far outweighs the number of electrons.
In a p-type material the hole is the majority carrier and the electron is the minority carrier.
When the fifth electron of a donor atom leaves the parent atom, the atom remaining acquires a net positive charge: hence the positive sign in the donor-ion representation. For similar reasons, the negative sign appears in the acceptor ion.
The n- and p-type materials represent the basic building blocks of semiconductor devices. We will find in the next section that the “joining” of a single n-type material with a p-type material will result in a semiconductor element of considerable importance in electronic systems.
That’s it for this topic, if you have any queries or doubts reguarding to this topic then feel free to mention in comment section below.
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