Question

The Group 3A/Group \(5 \mathrm{~A}\) semiconductors are composed of equal amounts of atoms from Group \(3 \mathrm{~A}\) and Group \(5 \mathrm{~A}\) - for example, InP and GaAs. These types of semiconductors are used in light- emitting diodes and solid-state lasers. What would you add to make a p-type semiconductor from pure GaAs? How would you dope pure GaAs to make an n-type semiconductor?

Short answer

To create a p-type semiconductor from pure GaAs, you can add a Group 3A element such as Boron (B), Aluminum (Al), Indium (In), or Thallium (Tl). In practice, Zinc (Zn) or Beryllium (Be) can also be used. For an n-type semiconductor, you can dope GaAs with a Group 5A element such as Nitrogen (N), Phosphorus (P), Antimony (Sb), or Bismuth (Bi). Silicon (Si) or Selenium (Se) can also be used in practice for n-type doping.

Step-by-step solution

Understanding Group 3A and 5A elements

Group 3A (or IIIA) elements include: B, Al, Ga, In and Tl. Group 5A (or VA) elements include: N, P, As, Sb and Bi. GaAs, the semiconductor mentioned in the exercise, is composed of gallium (Ga), a Group 3A element, and arsenic (As), a Group 5A element.

Understanding n-type and p-type semiconductors

n-type semiconductors are created by introducing an element that has more valence electrons (usually 5) than the original semiconductor, which will contribute free electrons to the material, thereby enhancing its conductivity. p-type semiconductors are created by introducing an element with fewer valence electrons (usually 3) than the original semiconductor. This introduction leads to the formation of "holes," which are positively charged, and enhances the conductivity of the material.

Creating a p-type semiconductor from GaAs

To create a p-type semiconductor, we need to dope GaAs with an element that has fewer valence electrons than Ga and As, which means we should look for an element from Group 3A. Possible dopants for p-type semiconductor in this case are: 1. Boron (B) 2. Aluminum (Al) 3. Indium (In) 4. Thallium (Tl) In practice, elements such as Zinc (Zn) or Beryllium (Be) can also be used to achieve p-type doping.

Creating an n-type semiconductor from GaAs

To create an n-type semiconductor, we need to dope GaAs with an element that has more valence electrons than Ga and As, which means we should look for an element from Group 5A. Possible dopants for the n-type semiconductor in this case are: 1. Nitrogen (N) 2. Phosphorus (P) 3. Antimony (Sb) 4. Bismuth (Bi) In practice, elements such as Silicon (Si) or Selenium (Se) can also be used to achieve n-type doping.

Key concepts

Group 3A Elements

When speaking of semiconductors, acknowledgment of the fundamental building blocks is crucial. Group 3A elements, positioned in the third column of the periodic table, have three valence electrons. These electrons play a vital role in the formation and functionality of semiconductors.

Key members include boron (B), aluminium (Al), gallium (Ga), indium (In), and thallium (Tl). In their pure form, these elements aren't quite suitable for applications requiring high conductivity. However, when they're mixed with other elements, especially those from Group 5A to form compounds like GaAs, they become the backbone of various semiconductor devices such as light-emitting diodes (LEDs) and transistors.

Group 5A Elements

Complementing the Group 3A elements are the Group 5A elements, found in the fifth column of the periodic table. These elements, including nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi), possess five valence electrons.

These additional valence electrons enable Group 5A elements to contribute to the conduction process in semiconductors, particularly when paired with Group 3A elements. In their combined form, as seen in GaAs (gallium arsenide), these materials are vital for the advancement of semiconductor technology. Their ability to easily donate electrons underpins the n-type doping process, enhancing the electrical conductivity of the semiconducting material.

P-Type Semiconductors

In the world of semiconductors, p-type materials are crucial for creating components that allow for the flow of positive charge. To achieve this, the pure semiconductor is 'doped', or intentionally contaminated, with an element that has one less valence electron than the material it is mixed into, such as Group 3A elements in a Group 4 semiconductor matrix.

This 'hole', or absence of an electron, acts as a positive charge carrier. When energy is applied, electrons from neighboring atoms can move to fill this hole, propagating a current of positive 'holes' moving in the opposite direction of the electron flow. This characteristic makes p-type semiconductors foundational in the creation of electronic devices like diodes and transistors.

N-Type Semiconductors

Conversely, the n-type semiconductors focus on the movement of electrons. Doping a pure semiconductor with a Group 5A element introduces an extra valence electron into the system. These excess electrons are loosely bound and can be easily dislodged, adding negatively charged carriers to the material.

The result is a material with improved electrical conductivity as these free electrons are now able to flow under the presence of an applied electric field. Since electrons are the primary charge carriers in n-type semiconductors, they are essential in applications requiring electron mobility, such as in the cathodes of LED lights or certain types of transistors.