Chapter 2 Characteristics of Semiconductor Materials

Question 1

Classifying Materials

Answer 1

Three different materials based on the flow of electric current through those materials: Conductors, Insulators, and Semiconductors.

Question 2

Conductors

Answer 2

Electrons readily flow through the material, high current-carrying capability. Carry one electron in valence shell that is easily free to conduct electricity.

Question 3

Conductivity Resistivity

Answer 3

Depends on material not geometry.

Question 4

Resistance

Answer 4

Opposition to current flow.

Question 5

Insulator

Answer 5

High resistance to current flow; rubber, plastic, glass, and ceramics. Typical insulating materials in semiconductors. (SiO2, Si3N4)

Question 6

Capacitance

Answer 6

Storage of electrical charge. Spacing between plates.

Question 7

Semiconductors

Answer 7

Can function as either conductors or insulators. Silicon is the most important material because 85% of all chips use silicon wafer substrate.

Question 8

How Semiconductors work?

Answer 8

Energy band gaps of insulators, conductor, and semiconductor.
Electrons in semiconductor jump from the valence band into the conduction bend when energy is supplied.

Question 9

Why Silicon?

Answer 9

1. Abundance of silicon 25% of earth crust.
2. Higher melting temperature: 1412 C wide processing range.
3. Wider temperature range of operation: increase in application and reliability.
4. Natural growth of SiO2: chemical barrier to protect Si from external contamination.

Question 10

Doping

Answer 10

Is the process of adding certain elements to pure silicon to enhance its material properties; conductivity or resistivity.

Question 11

Doping Materials

Answer 11

Silicon is located in group 4A of the periodic table and has four valence electrons. Elements from the two adjacent groups are commonly used for doping: Group 3A (Boron) and 5A (Nitrogen).

Question 12

Group III A

Answer 12

Trivalent: 3 valence electrons, increase number of holes for positive doping or p-type.

Question 13

Group VA

Answer 13

Pentavalent: 5 valence electrons, increase the number of free electrons for negative doping or n-type.

Question 14

Resistivity of Doped Silicon

Answer 14

Depends on the concentration of the dopants, there is less concentration of n-type than p-type. Takes less energy to move an electron than to move a hole.