Silicon doped with gallium forms ______.
p-type semiconductor
Understanding Semiconductor Doping: Silicon and Gallium
This question asks about the type of semiconductor formed when Silicon is doped with Gallium. To answer this, we need to understand the concept of semiconductor doping and the properties of Silicon and Gallium.
What are Semiconductors?
Semiconductors are materials that have electrical conductivity between that of a conductor (like copper) and an insulator (like glass). Common examples include Silicon (Si) and Germanium (Ge). These materials are typically from Group 14 of the periodic table and have 4 valence electrons, allowing them to form covalent bonds.
What is Doping?
Doping is the process of intentionally adding impurities to an intrinsic (pure) semiconductor to alter its electrical properties. By adding specific types of impurity atoms, we can increase the number of charge carriers (electrons or holes) and thus increase the conductivity of the semiconductor.
Silicon (Si) and Gallium (Ga)
- Silicon (Si): Silicon is a Group 14 element. In its pure crystalline form, each Silicon atom forms covalent bonds with four neighboring Silicon atoms, sharing its 4 valence electrons.
- Gallium (Ga): Gallium is a Group 13 element. It has 3 valence electrons.
Doping Silicon with Gallium
When Gallium atoms are introduced into the Silicon crystal structure, they replace some Silicon atoms. Since Gallium has only 3 valence electrons compared to Silicon's 4, it cannot complete all four covalent bonds with its neighboring Silicon atoms. One bond will be deficient by one electron, creating a 'hole'.
This hole behaves like a positive charge carrier. When an electric field is applied, electrons from nearby Silicon atoms can move into these holes, causing the holes to move through the crystal lattice. The movement of holes contributes to the electric current.
Because the doping impurity (Gallium) creates 'holes' which are majority charge carriers, this type of doping results in a p-type semiconductor. Group 13 elements are called acceptor impurities because they 'accept' an electron by forming a hole.
| Semiconductor Type | Dopant Group | Valence Electrons of Dopant | Created Charge Carrier | Majority Charge Carrier | Dopant Name |
|---|---|---|---|---|---|
| n-type | Group 15 (e.g., P, As, Sb) | 5 | Free Electron | Electrons | Donor |
| p-type | Group 13 (e.g., B, Al, Ga, In) | 3 | Hole | Holes | Acceptor |
Analyzing the Options
- n-type semiconductor: This is formed when a Group 14 semiconductor like Silicon is doped with a Group 15 element (like Phosphorus), which introduces extra electrons. Gallium is from Group 13, not Group 15, so this option is incorrect.
- superconductor: A superconductor is a material that conducts electricity with zero resistance below a critical temperature. Doping Silicon with Gallium does not typically make it a superconductor. This is incorrect.
- insulator: An insulator is a material that resists the flow of electric current. Doping a semiconductor increases its conductivity, it does not turn it into an insulator. This is incorrect.
- p-type semiconductor: This is formed when a Group 14 semiconductor like Silicon is doped with a Group 13 element (like Gallium), which introduces holes as majority charge carriers. This matches our understanding of doping Silicon with Gallium. This option is correct.
Therefore, Silicon doped with Gallium forms a p-type semiconductor.
Revision Table: Silicon Doping Concepts
| Concept | Description | Relevance to Silicon Doping |
|---|---|---|
| Silicon (Si) | Group 14 Semiconductor, 4 valence electrons | Base material being doped |
| Gallium (Ga) | Group 13 Element, 3 valence electrons | Dopant impurity |
| Doping | Adding impurities to change conductivity | Process involved |
| Hole | Absence of an electron in a covalent bond | Majority carrier in p-type semiconductor |
| p-type Semiconductor | Semiconductor with holes as majority carriers | Result of doping Silicon with Gallium |
Additional Information: Semiconductor Physics
Intrinsic semiconductors have a limited number of charge carriers (electrons and holes generated by thermal energy). Doping dramatically increases the number of either electrons (n-type) or holes (p-type), making the semiconductor extrinsic. The conductivity of an extrinsic semiconductor is much higher than that of an intrinsic semiconductor at room temperature.
In p-type semiconductors, the concentration of holes (p) is much greater than the concentration of electrons (n), i.e., \(p \gg n\). In n-type semiconductors, the concentration of electrons (n) is much greater than the concentration of holes (p), i.e., \(n \gg p\).
The product of electron and hole concentrations in a semiconductor at thermal equilibrium remains constant at a given temperature and is equal to the square of the intrinsic carrier concentration (\(n_i\)): \(np = n_i^2\).
Important Questions from Semiconductors
Energy required to break the covalent bond of a semiconductor is:
In a pure semiconductor
When a p-n junction is reverse blased, its depletion region
Semiconductors have a ______ energy gap
- The electron valence of a copper atom is:
