What is a semiconductor?
Materials whose conductivity falls between those of conductors and insulators
Semiconductors are “part-time” conductors whose conductivity can be controlled.
Name two common materials used to build semiconductor devices.
- Silicon
- Germanium
Silicon is the most common material, while germanium is another option.
What are conductors?
Materials that permit flow of electrons (e.g., gold, silver, copper)
Conductors allow electrical current to pass through them easily.
What are insulators?
Materials that block flow of electrons (e.g., rubber, glass, Teflon)
Insulators prevent electrical current from passing through.
What are the valence electrons in a pure silicon wafer?
4 valence electrons
These electrons are involved in covalent bonding within the crystalline structure.
What happens when phosphorus is added to silicon?
Creates N-type silicon with free electrons
Phosphorus has 5 valence electrons, and the extra electron becomes a free charge carrier.
What is P-type silicon?
Silicon doped with trivalent impurities like boron
Boron creates holes that act as positive charge carriers.
What is a diode?
A 2 lead semiconductor that acts as a one way gate to electron flow
Diodes allow current to pass in only one direction.
What is the difference between forward-biased and reverse-biased diodes?
- Forward-biased: current flows
- Reverse-biased: current is blocked
Forward bias occurs when the anode is at a higher potential than the cathode.
What is the water analogy for diodes?
Water pressure analogy for current flow
When pressure overcomes resistance, flow occurs; otherwise, it is blocked.
What is the function of a transistor?
Acts as an electrically controlled switch or current amplifier
A small voltage/current at the control lead can control a larger current flow.
Name the types of transistors.
- Bipolar Junction Transistor (BJT)
- Junction Field Effect Transistor (JFET)
- Metal Oxide Semiconductor FET (MOSFET)
Each type has unique characteristics and applications.
What is a light-emitting diode (LED)?
A 2 lead semiconductor device that emits light when forward-biased
LEDs can emit visible or infrared light.
What is the maximum forward voltage for visible-light LEDs?
Approximately 1.8V
This voltage is necessary for the LED to conduct and emit light.
What happens if the current through an LED exceeds its maximum allowed value?
The LED will be damaged
Current control is essential to prevent destruction of the LED.
What is the purpose of a resistor in series with an LED?
To control current through the LED
A resistor limits the current to safe levels for the LED.
What is the maximum forward voltage for LEDs?
1.8V
This is the typical voltage required for LEDs to operate effectively.
Typical operating currents for LEDs range from _______ to _______.
1 to 3mA
This range indicates the current levels at which LEDs are commonly operated.
What are the typical brightness levels for LEDs at 1mA and 2mA?
- 1.0 to 3.0mcd at 1mA
- 3.0mcd at 2mA
Brightness levels can vary based on the current supplied to the LED.
What is a blinking LED used for?
Indicator flashers
Blinking LEDs contain a miniature integrated circuit that causes them to flash.
Describe the structure of a tricolor LED.
- Two LEDs in parallel
- One LED is red or orange
- One LED is green
Current flow in one direction turns one LED ON while the other remains OFF, and vice versa.
What is the maximum voltage rating for a tricolor LED?
3V
This rating indicates the maximum voltage that can be applied to the tricolor LED.
What is a 7-segment LED display used for?
Displaying numbers and other characters
It consists of 7 individual LEDs that light up to form different characters.
How does an LED work?
By joining n-type and p-type semiconductors to form a pn junction
Electrons excited across the junction emit photons when they combine with holes.
