In this note, we are going to learn about N Type Semiconductor, about its formation and internal structure. Welcome to Poly Notes Hub, a leading destination for Engineering Notes.
Author Name: Arun Paul.
What is N Type Semiconductor?
When a small amount of pentavalent is added to a pure semiconductor, it is known as an n type semiconductor.
The addition of pentavalent impurity provides a large number of free electrons in the semiconductor crystal. Typical pentavalent impurities are arsenic (At. No. 33) and antimony (At. No. 51). Such Impurities that produce n-type semiconductors are known as donor impurities because they donate or provide free electrons to the semiconductor crystal.
To explain the formation of n type semiconductors, consider a pure germanium crystal. We know that the germanium atom has four valence electrons. When a small amount of pentavalent impurity like arsenic is added to germanium crystal, a large number of free electrons become available in the crystal. The reason is simple. Arsenic is pentavalent i.e. its atom has five valence electrons.
An arsenic atom fits in the Germanium Crystal so that its four valence electrons form covalent bonds with four germanium atoms. The fifth valence electrons of the arsenic atom find no place in co-valent bonds and are thus free as shown in the above figure. Therefore, one free electron will be available in the germanium crystal for each arsenic atom added. Though each arsenic atom provides one free electron, an extremely small amount of arsenic impurity provides enough atoms to supply millions of free electrons.
📌 Majority and Minority carriers: This type of semiconductor produces a large number of free electrons and a few number holes are also created by it. For this reason, Electrons are the Majority Carrier in this type of Semiconductor and Holes are the Minority Carrier in this type of Semiconductor.
Important Points of N Type Semiconductor:
- Doping: N-type semiconductors are formed by doping a semiconductor material with elements such as phosphorus or arsenic, which have additional electrons in their outer shell.
- Majority Carriers: In N-type semiconductors, electrons account for the majority bulk of charge carriers. The additional electrons from the dopant atoms are responsible for the material’s conductivity.
- Energy Band Structure: An N-type semiconductor’s energy band diagram shows a partially filled conduction band due to the availability of extra electrons.
- Conductivity Level: N-type semiconductors have better conductivity than intrinsic or undoped semiconductors due to the existence of more charge carriers.
- Barrier Height: The difference in Fermi levels between an N-type and a P-type semiconductor determines the potential barrier at the junction, which is critical to the operation of semiconductor devices.
Energy Band Diagram of N Type Semiconductor
The addition of pentavalent impurity has produced several conduction band electrons i.e., free electrons. The four valence electrons of the pentavalent atom form covalent bonds with four neighboring germanium atoms. The fifth leftover valence electron of the pentavalent atom cannot be accommodated in the valence band and travels to the conduction band.
Why N Type Semiconductor is called so?
The naming system for semiconductor kinds, such as N-type and P-type, is derived from the behavior of charge carriers within the material.
In an N-type semiconductor, the bulk of charge carriers are negative (electron). This is accomplished by doping the semiconductor material with elements containing additional electrons in their outer shell, such as phosphorus or arsenic. These extra electrons, known as donor electrons, are responsible for the material’s conductivity.
The term “N-type” refers to the fact that the material contains an overabundance of negative charge carriers. The letter “N” stands for negative. In contrast, in a P-type semiconductor, the bulk of charge carriers are positive “holes” (missing electrons) generated by doping the semiconductor material with elements like boron or gallium, which have less electrons in their outer shells. In P-type semiconductors, the letter “P” stands for “positive.”