Problem 51 - General Chemistry: Principles and Modern Applications

Question

Which of the following substances, when added in trace amounts to silicon, would produce a \(p\) -type semiconductor: (a) sulfur, (b) arsenic, (c) lead, (d) boron, (e) gallium arsenide, (f) gallium? Explain.

Step-by-Step Solution

Answer

Boron and Gallium can create a p-type semiconductor when added to silicon in trace amounts.

Step 1: Valence Electrons of Silicon

Silicon, the base material in this scenario, has four valence electrons in its outermost shell. This information will be used to compare with the valence electrons of the given substances.

Step 2: Valence Electrons of the Tracers

Determine the number of valence electrons for each of the given substances. Sulfur has 6, Arsenic has 5, Lead has 4, Boron has 3, Gallium Arsenide is a compound and Gallium itself has 3.

Step 3: Identify p-type Semiconductor Materials

In order to create a p-type semiconductor, we need to introduce a substance that has one less valence electron than Silicon. In our case, Boron and Gallium, both having 3 valence electrons, meet the criteria. Therefore, adding either Boron or Gallium to silicon can create a p-type semiconductor.

Key Concepts

Silicon Doping

Silicon doping involves intentionally introducing impurities into pure silicon, a process that transforms its electrical properties. This is crucial in creating semiconductors, which are fundamental components of modern electronics.
When we talk about doping in semiconductors, we essentially mean adding a substance in small amounts to silicon to alter its conductance. For a substance to effectively dope silicon and create a specific type of semiconductor, it should have a different number of valence electrons than silicon.
To create a p-type semiconductor, we utilize substances with fewer valence electrons than silicon, such as Boron or Gallium. This creates "holes" in the silicon structure—a lack of electrons where one should be, allowing for the flow of positive charge. This controlled introduction of elements forms the basis of tailoring silicon for specific electronic applications.

Valence Electrons

Valence electrons are the outermost electrons of an atom and determine how an element interacts with others. In the context of semiconductors, these electrons play a key role.
Silicon, for instance, has four valence electrons. These electrons form covalent bonds with another silicon atom, creating a stable and structured lattice. To create a p-type semiconductor, we need to add atoms with fewer valence electrons than silicon, usually three.
Boron and Gallium, with three valence electrons, are perfect candidates. When inserted into the silicon lattice, they create a vacancy or "hole" where a silicon atom would normally have an electron. This hole acts as a positive charge carrier, facilitating the creation of a p-type semiconductor.

Semiconductor Materials

Semiconductor materials are critical in the world of electronics. They possess electrical conductivity between a conductor and an insulator, making them versatile. The conductivity of semiconductors can be modified through a process called doping.
Silicon, a widely used semiconductor material, forms the backbone of modern electronic devices due to its abundant availability and favorable properties.

• Intrinsic Semiconductors: Pure silicon with balanced electron and hole concentrations.
• Extrinsic Semiconductors: Silicon modified by doping to form p-type or n-type semiconductors.

Through doping with elements like Boron or Gallium, silicon becomes a p-type semiconductor. This modification is vital for the development of electronic components like diodes and transistors, allowing for advancements in technology.