Semiconductors Flashcards
What is a semiconductor?
A semiconductor is a material that is halfway between a conductor and an insulator in terms of electrical conductivity. It is generally a crystalline solid material that conducts electrical current under certain conditions.
What characterizes an intrinsic semiconductor?
An intrinsic semiconductor is chemically pure, contains no impurities, and has perfect regularity in its crystal structure. It has a small energy gap between the valence band and the conduction band.
How do semiconductors behave at very low temperatures?
At very low temperatures, all outer electrons are in the valence band, making the semiconductor a perfect insulator as there are no free electrons in the conduction band.
What are the three main processes occurring in an intrinsic semiconductor?
- Electron excitation into the conduction band.
- Mobility of electrons in the conduction band and holes in the valence band.
- Recombination of electrons and holes.
What happens to semiconductors at normal room temperature?
At normal room temperature, many electrons gain enough energy to jump to the conduction band, allowing them to take part in electrical conduction.
What is a ‘positive hole’ in a semiconductor?
A ‘positive hole’ is a vacancy left in the valence band when an electron jumps to the conduction band. This hole can move through the crystal lattice as electrons from neighboring atoms fill it.
What are some common intrinsic semiconductors?
- Silicon (atomic number 14)
- Germanium (atomic number 32)
What is an extrinsic semiconductor?
An extrinsic semiconductor is created by adding controlled amounts of impurities to an intrinsic semiconductor, a process known as doping, which greatly increases its electrical conductivity.
What are the two types of extrinsic semiconductors?
- N-type, which enhances electron flow in the conduction band.
- P-type, which enhances positive-hole flow in the valence band.
What is the role of impurities in N-type semiconductors?
In N-type semiconductors, pentavalent impurities (such as arsenic, antimony, and phosphorus) donate free electrons that can be lifted into the conduction band to participate in electrical conduction.
