Week 6 Questions

1. Examples of semiconductors are diodes and transistors. Also microprocessors use CMOS (Complimentary metal-oxide-semiconductor) technology.
2. Because the purity of refined silicon is 99.999999999%
3. When phosphorus with 5 valence electrons mixes with silicon which has 4 valence electrons, phosphorus and silicon bond, but one electron (negative charge) escapes and becomes a free electron. This is an N-type semiconductor. When Boron with 3 valence electrons mixes with silicon which has 4 valence electrons, boron and silicon bond, but there is one electron missing which can be considered as a positively charged electron. This is P-type semiconductor.
4. A diode allows current to flow in one direction only. At the P-N junction, the free, negatively charged electrons from the N-type semiconductor are absorbed by the positively charged electrons from the P-type semiconductor. This forms a potential barrier that can be broken by applying voltage.
5. Rectification is a property that allows current to flow only in one direction.
6. Various colors of light can be created depending on the raw material of the semiconductor that emits light of a specific wavelength. Examples are traffic lights and backlighting of mobile phones.
7. The current that flows from the base to the emitter is called "base current," and when the base current flows, current will also flow from the collector to the emitter, and this is called "collector current."
8. Unlike regular switches, transistors have no physical contact, meaning that they don't wear out and are less likely to fail. Also, since transistors can be turned on/off rapidly, control can be fine tuned.