Intrinsic vs Extrinsic Semiconductor
It is remarkable that the modern electronics is based on one type of material, semiconductors. Semiconductors are materials which have an intermediate conductivity between conductors and insulators. Semiconductor materials were used in electronics even before the invention of semiconductor diode and transistor in 1940’s, but after that semiconductors found vast application in the field of electronics. In 1958, the invention of the integrated circuit by Jack Kilby of Texas instruments elevated the use of semiconductors in the field of electronics to an unprecedented level.
Naturally semiconductors have their property of conductivity due to free charge carriers. Such a semiconductor, a material, which naturally shows semiconductor properties, is known as an intrinsic semiconductor. For the development of advanced electronic components, semiconductors were improved to perform with greater conductivity by adding materials or elements, which increase the number of charge carriers in the semiconductor material. Such a semiconductor is known as an extrinsic semiconductor.
More about Intrinsic Semiconductors
Conductivity of any material is due to the electrons released to the conduction band by the thermal agitation. In the case of intrinsic semiconductors, the number of electrons released is relatively lower than in the metals, but greater than in the insulators. This allows a very limited conductivity of current through the material. When the temperature of the material is increased, more electrons enter the conduction band, and hence the conductivity of the semiconductor also increases. There are two types of charge carriers in a semiconductor, the electrons released into the valence band and the vacant orbitals, more commonly known as the holes. The number of holes and electrons in an intrinsic semiconductor are equal. Both holes and electrons contribute to the current flow. When a potential difference is applied electrons move towards the higher potential and holes move towards the lower potential.
There are many materials that act as semiconductors, and some are elements and some are compounds. Silicon and Germanium are elements with semiconducting properties, while Gallium Arsenide is a compound. Generally elements in group IV and compounds from the elements of groups III and V, such as Gallium Arsenide, Aluminum Phosphide and Gallium Nitride show intrinsic semiconductor properties.
More about Extrinsic Semiconductors
By adding different elements, the semiconductor properties can be refined to conduct more current. The adding process is known as doping while, the material added is known as the impurities. Impurities increase the number of charge carriers within the material, allowing better conductivity. Based on the carrier supplied, the impurities are classified as acceptors and donors. Donors are materials which have unbound electrons within the lattice, and acceptors are materials which leave holes in the lattice. For group IV semiconductors, group III elements Boron, Aluminum act as acceptors, while group V elements Phosphorus and arsenic act as donors. For group II-V compound semiconductors, Selenium, Tellurium act as donors, while Beryllium, Zinc and Cadmium act as acceptors.
If a number of acceptor atoms are added as impurity, the number of the holes increase and the material has excess of positive charge carriers than before. Therefore, the semiconductor doped with acceptor impurity is called a Positive-type or P-Type Semiconductor. In the same manner a semiconductor doped with donor impurity, which leave the material in excess of electrons, is called a Negative type or N-Type semiconductor.
Semiconductors are used to manufacture different types of diodes, transistors and related components. Lasers, Photovoltaic cells (Solar cells), and photo detectors also use semiconductors.
What is the difference between Intrinsic and Extrinsic Semiconductors?
- Semiconductors which are not doped are known as intrinsic semiconductors, while a semiconductor material doped with impurities is known as an extrinsic semiconductor.
- Number of positive charge carriers (holes) and the negative charge carriers are equal in intrinsic semiconductors, while by adding impurities the number of charge carriers are changed; hence unequal in extrinsic semiconductors.
- Intrinsic semiconductors have relatively lower conductivity than the extrinsic semiconductors.