Semiconductor and Transistor

What is Semiconductor?

A semiconductor is a material that conducts electricity more than an insulator like glasses but less than a pure conductor like metals. Semiconductors that we used in different electronic devices are two types like n-type and p-type semiconductors. An n-type semiconductor is obtained when silicon or germanium is doped with an element of group-15 like phosphorus, arsenic, or antimony. A p-type semiconductor is obtained when silicon or germenium is doped with an element of group-13 like boron, aluminum, or galium.

n-type semiconductor formation by doping phosphorus on silicon
Image Source: https://www.priyamstudycentre.com/2021/09/semiconductor.html
p-type semiconductor formation by doping boron on silicon
Image Source: https://www.priyamstudycentre.com/

Today we used different types of semiconductors and insulators in thousand of types of electronic devices like computers, smartphones, appliances, gaming hardware, and medical equipment. Semiconductor technology can be developed in the 1950s with the introduction of germanium transistors. Today, the production of very pure silicon is easier than germanium. Methods for the production of ultrapure silicon were developed in the late 1960s. Therefore, silicon transistors are now widely used due to their superior quality. Other semiconducting materials have also been developed and introduced mainly from the elements in the neighboring groups like group-13 and group-14.

We found that semiconductor behavior depends on the small energy gap between the highest occupied energy levels or valence band and the lowest unoccupied energy levels or valence band. The bandgap decreases sharply from carbon (diamond) to silicon to tin. Diamond is an insulator. Pure silicon is an insulator at room temperature. If silicon is dropped with an element of group-15 like phosphorus, arsenic, or antimony, an n-type semiconductor is obtained. If doping is done by an element of group-13 like boron, aluminum, or galium, a p-type semiconductor is obtained.

What is a transistor?

The combination of an n-pe sample of silicon with one of p-type gives rise to an n-p junction. Electrons can flow from n to p and holes from p to n and the current passes more easily in one direction than the other. It can act as a diode. Two n-type Si separates by weakly p-type silicon produce an n-p-n junction or a transistor.

Image Source: https://learn.sparkfun.com/tutorials/transistors/all

Extremely small stable single-crystal transistors may be prepared by exposing selected areas on a single crystal n-type silicon wafer to the vapour of a group-13 element when the impurity atoms diffuse to form a layer of p-type silicon semiconductor. These areas are then covered with a protective layer of SiO2 which is toughened by exposure to UV radiation. At other desirable places, the layer is etched with HF and exposed to the vapour of a group-5 element.

In this manner, a patterned deposit of n-p-n type Si is obtained which is again covered with a protective layer of SiO2. Metals are deposited at suitable places to connect the n and p-regions into an integrated circuit.

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Chemistry is the study of properties, structure, composition of atoms, ions, and molecules. This materials provides different Chemistry topics and questions

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