Lecture 1-3.3 (Quiz 1)

Valence electrons

are those electrons that occupy the outer shell.

Copper

It has only one electron in its valence band, which can easily escape to the conduction band, leaving behind a positive ion (the core).

Insulators

have tightly bound electrons with few electrons available for conduction.

eight valence electrons

Best insulators have ________

Semiconductors

are between conductors ability to conduct electricity

4 valence electrons

How many valence electrons does Silicon and Germanium have?

covalent bonds

Unlike metals, silicon forms strong ________(shared electrons) with its neighboring atoms making a crystalline structure

covalent bonds

is a type of chemical link where two atoms share one or more pairs of electrons so that both can achieve a stable outer shell.

hole

here is a small number of electrons in the lattice which will become loose from their atoms, leaving behind an empty space called a "____"

Electron current

The conduction band electrons are free to move under the influence of an electric field.

Hole current

The bound (valence) electrons move between atoms, effectively moving “holes” from one atom to another as illustrated. Holes act like positive charges, with their own mobility.

decreases

Electric current in the conductor _________ with the increase in temperature

increases

Electric current in the semiconductor _______with the increase in temperature.

In a semiconductor as temperature increases, resistance decreases, because when the semiconductor is heated the vibration causes the covalent bonds to break therefore creating more holes and electrons to pass through.

Explain the properties of semiconductor with the increase of temperature

In a conductor as temperature increases, resistance increases, because when the conductor is heated the vibration opposes the electrons passing through.

Explain the properties of conductor with the increase of temperature

doping

Since semiconductors are generally poor conductors, their conductivity can be drastically increased by the controlled addition of impurities to the intrinsic (pure) semi-conductive material. This process, called ______

Extrinsic Materials

Materials that are doped or impure

1. N-type

2. P-type

There are two types of extrinsic materials

N-type material

Created by introducing impurity atoms (doping) that have 5 valence electrons (pentavalent)

donors

As each impurity atom “donates” one

electron, pentavalent atoms are generally

known as “______”

donors

N-type are _____

N-type

This allows four out of the five orbital electrons bonds with its neighboring silicon atoms leaving one “free electron” to become mobile when an electrical voltage is applied (electron flow).

free electrons, resulting/postive holes

N-type material ________ is called “Majority Carriers” while the ___________ are called “Minority Carriers”.

P-type

Created by introducing impurity atoms (doping) that have 3 valence electrons (trivalent)

acceptor atoms

Diffused impurities with three valence electrons are called ___________ as they are continually “accepting” extra or free electrons

Boron, B

is commonly used as a trivalent additive.

positive/resulting , free electrons

In P-type materials _______ holes are called “Majority Carriers” while the ___________ are called “Minority Carriers”.

N-type

material the electron is called the majority carrier and the hole the minority carrier.

P-type

material the hole is called the majority carrier and the

electron the minority carrier.

PN junction

conduction electrons move to the p-region, and fall into holes. Filling a hole makes a negative ion and leaves behind a positive ion in the n-region

Conduction electrons move from the n-region to the p-region. This creates negative ions in the p-region and leaves positive ions in the n-region.

What happens when a p-n region junction is formed?

Depletion Region

a thin region that is depleted of free charges a the boundary which prevents further charge migration.

a thin barrier is formed because of the formation of negative ions in the p region therefore stopping electrons from the n region to cross the p region

Function of the Depletion Region

high resistance

Intrinsic semiconductor (not doped): ________ (since very few free electrons or holes).

low resistance

N-type semiconductor (doped with donors): ___________ (due to lots of free electrons)

low resistance

P-type semiconductor (doped with acceptors): ____________ (due to lots of holes)

• Silicon(Si)

• Germanium(Ge)

• Gallium Arsenide(GaAs)

Materials commonly used in the development of semiconductor devices:

Barrier potential (V0)

There exists a potential difference across the depletion layer and is called

silicon = 0.7 V

germanium = 0.3 V

What is the barrier potential of both silicon and germanium?

• No bias

• Reverse bias

• Forward bias

What are the three operating conditions of a diode

No bias

No external voltage is applied: VD = 0 V ID = 0 A

Reverse Bias

• The reverse voltage causes the depletion region to widen.

• The electrons in the n-type material are attracted toward the positive terminal of the voltage source.

• The holes in the p-type material are attracted toward the negative terminal of the voltage source.

Forward Bias

• The forward voltage causes the depletion region to narrow.

• The electrons and holes are pushed toward the p-n junction.

• The electrons and holes have sufficient energy to cross the p-n junction.

• very small current when it is reversed biased

• small voltage across when it is forward biased.

Practical Diode Characteristics

breakdown voltage

If we apply excess voltage on a real diode in the reverse direction, the diode will be destroyed and will let current flow in the reverse direction

1. Light-emitting diode

2. Diode arrays

There are two types of diodes

Light-Emitting diode (LED)

• An ___emits photons when it is forward biased.

• The color of light emitted by the diode is determined by the type of material used in doping

2V to 3V

What is the range of the forward bias voltage of a light-emitting diode

Diode arrays

Multiple diodes can be packaged together in an integrated circuit (IC)

Common anode

Common cathode

Anode | Cathode

Where is cathode and anode located

Diode

is a semiconductor device that allows electrical current to flow in one direction only.

Anode and Cathode

What are the two terminals of the diode

reverse biased

when voltage at the anode is lower than the voltage at the cathode

forward bias

When the voltage at the anode is higher than the voltage at the cathode

laod-line analysis

The operating point of a diode can be determined by a _________ of the voltage- current characteristic.

Operating Point (Q-point)

is given by the intersection of the load line and the diode characteristic.

Q point

is the quiescent operating point

ID = 0A

VD = E if

VD = 0V

ID = E/R if

rectification

the AC current is converted to DC current.

AC-DC converter.

Rectifier is also called an _______

half-wave rectification

he process of removing one-half of the input ac signal to establish a dc level is called

Vdc = 0.318 x Vm

What is the formula for the DC level voltage for the ideal diode

Vdc = 0.318(Vm - Vk)

What is the formula for the the DC level voltage for the practical diode

Vmo = Vm

What is the the maximum voltage for the Ideal diode

Vmo = Vm-Vk

What is the maximum voltage for the practical diode

Full-wave rectifier

consists of four diodes connected between an ac voltage source and a load (resistor R) as shown.

Vsec = nVpri

What is the transformer voltage formula

Zener diode

• is a silicon pn junction device

• Designed for operation in the reverse region.

Zener diode

can be used as a type of voltage regulator for providing stable reference voltages