A semiconductor is a material whose resistivity falls between that of conductors and insulators. These materials have a negative temperature coefficient, meaning their resistance increases as temperature decreases, and vice versa. When we add a suitable metallic impurity, the electrical properties of the semiconductor change significantly.
In this article, we will focus on the key differences between intrinsic and extrinsic semiconductors based on parameters like doping level, conductivity, and charge density.
The detailed difference between the two types of semiconductors is provided below:
Intrinsic Semiconductor
When we talk about intrinsic semiconductors, we’re referring to those pure materials that don’t undergo doping or have impurities added. In these semiconductors, the number of free electrons in the conduction band is equal to the number of holes in the valence band. This balance results in low electrical conductivity. If you think about it, the conductivity of intrinsic semiconductors primarily depends on temperature. Some common examples you might come across are the crystalline forms of pure silicon and germanium.
Extrinsic Semiconductor
Now, let’s shift our focus to extrinsic semiconductors. These are made by adding a small amount of impurity to a pure semiconductor through a process known as doping. Unlike intrinsic semiconductors, the number of electrons and holes in extrinsic semiconductors isn’t equal, which is why their electrical conductivity is much higher. You’ll find that the conductivity in these materials depends on both temperature and the amount of impurity we add. Some examples of extrinsic semiconductors include germanium or silicon that have been doped with impurities like arsenic, aluminum, phosphorus, gallium, indium, and antimony.
Difference Between Intrinsic and Extrinsic Semiconductor
| Property | Intrinsic Semiconductor | Extrinsic Semiconductor |
|---|---|---|
| Electrical Conductivity | Has low electrical conductivity. | Offers higher electrical conductivity. |
| Source of Charge Carriers | Charge carriers are generated only due to thermal energy. | Carriers arise from both thermal energy and added impurities (doping). |
| Fermi Level Position (at 0K) | Lies exactly between the conduction and valence bands. | Depends on type: near conduction band (n-type) or valence band (p-type). |
| Charge Carrier Ratio | Majority and minority carriers are equal (ratio is 1:1). | Majority carriers far outnumber minority carriers (ratio ≠ 1). |
| Conductivity at 0 Kelvin | Does not conduct electricity at absolute zero. | Can still conduct electricity at 0 Kelvin. |
| Operating Temperature Range | Operates efficiently at lower temperatures. | Designed to perform well even at higher temperatures. |
| Dependency of Conductivity | Conductivity is affected only by temperature. | Influenced by both temperature and doping concentration. |
| Examples | Pure silicon and pure germanium crystals. | Doped silicon or germanium with elements like As, P, Sb (n-type) or B, Al, In (p-type). |
Summary
To sum it up, intrinsic semiconductors stay pure without any impurities, while extrinsic semiconductors are intentionally doped with specific impurities to enhance their electrical properties. If you’re looking for examples, silicon and germanium are the go-tos for intrinsic semiconductors, while extrinsic semiconductors come from adding elements like arsenic, aluminum, phosphorus, gallium, indium, and antimony to pure germanium or silicon.