Question

Two types of semiconductors, \(n\) - and p-types, are made by doping a host such as silicon with a small amount of an element that has more or fewer valence electrons than the host. How do you think doping Si with As to give an n-type semiconductor would change the electronic conductivity of the material?

Short answer

Doping silicon with arsenic increases the electronic conductivity by adding extra free electrons as charge carriers.

Step-by-step solution

Understanding n-type Semiconductors

The goal of doping is to introduce additional charge carriers. In an n-type semiconductor, the semiconductor is doped with an element that has more valence electrons than the semiconductor itself. For silicon (Si), which has four valence electrons, arsenic (As), which has five valence electrons, can be used as a dopant.

Effect of Doping with Extra Electrons

When an arsenic atom replaces a silicon atom in the lattice, there is one extra electron per arsenic atom because arsenic has five valence electrons, while silicon has only four. This extra electron is not needed for bonding, so it becomes free to move throughout the crystal as a conduction electron.

Increased Electronic Conductivity

The presence of these free electrons increases the number of charge carriers available for conduction in the semiconductor. Consequently, the conductivity of the material increases because the mobile electrons facilitate the flow of electric current.

Key concepts

Doping

Doping is a fundamental technique used in the creation of semiconductors. It involves adding a small amount of an extra element to a pure semiconductor to enhance its electrical properties. For example, when we talk about doping silicon (Si) to make an n-type semiconductor, like in the case of introducing arsenic (As), we're actually inserting atoms with more valence electrons compared to silicon's four.

• This process effectively introduces additional free electrons to the system, which directly impacts electrical conductivity.
• The dopant element (like arsenic) with more valence electrons acts as a donor of extra electrons.

By adding these extra electrons, the doped semiconductor material provides better pathways for electricity to flow. This modification is crucial for creating devices with specific electrical characteristics, thereby tailoring semiconductors for tasks like switching or amplifying electronic signals.

Electronic Conductivity

Electronic conductivity refers to the ability of a material to conduct electric current. In semiconductors, conductivity is primarily managed by the number of charge carriers available. In an n-type semiconductor, doping increases the number of conduction electrons, which are the primary charge carriers.

• When elements like arsenic are introduced, they donate additional electrons, increasing the electron concentration within the silicon lattice.
• This increase in free electrons enhances the material's overall conductivity.

The extra electrons are not used for bonding but instead move freely through the material. This mobility of electrons is a key feature, as it enables the crystal to conduct electricity more efficiently. When an external electric field is applied, these electrons move towards the positive pole, thus allowing for significant current flow. With more free electrons available, the semiconductor responds better to electrical inputs, increasing its utility in various applications, from computing to communication technologies.

Silicon

Silicon is one of the most widely used materials in electronics, primarily due to its abundant availability and useful semiconducting properties. It has four valence electrons, making it an excellent base material for semiconductors. In its pure form, silicon has a relatively low conductivity. This changes dramatically with doping. For instance, adding arsenic introduces extra electrons into the silicon lattice, converting it into an n-type semiconductor.

• Arsenic, having five valence electrons, provides one additional free electron per atom compared to silicon.
• This modification results in enhanced electronic conductivity, which is essential for the performance of semiconductor devices.

Besides, silicon serves as the backbone in many modern electronic advancements. Its ability to be precisely doped makes it versatile and invaluable in producing integrated circuits and various other components. Therefore, silicon's role in the electronics industry is pivotal, as it continuously facilitates more efficient and miniaturized technology solutions.