Semiconductor Diodes: Characteristics and Applications

Semiconductor Diodes

• The construction of any electronic device or integrated circuit starts with a semiconductor material.
• Semiconductors are elements with conductivity between that of a good conductor and an insulator.

General Characteristics

• Semiconductors conduct electricity less than metals but more than insulators.
• Common semiconductor materials are silicon (Si), germanium (Ge), carbon (C), and gallium arsenide (GaAs).
• Silicon is the most widely used semiconductor in electronics.
• Diodes, transistors, and ICs are often made from silicon.
• Semiconductors have four valence electrons and their conductivity changes based on the environment.

Applications

• Transistors, made from semiconductors, are used in logic elements, memory, and computer communication modules.

Wafer

• Single crystal semiconductors like Germanium (Ge) and Silicon have a repetitive crystal structure.
• Compound semiconductors like Galium Arsenide (GaAs)), Cadmium Sulfide (CdS), Galium Nitride (GaN) and Galium Arsenide Phosphide (GaAsP) consist of two or more semiconductor materials with different atomic structures
• Ge, Si and GaAs are used most frequently in electronic devices.

Timeline

• 1939: Diode discovery using Germanium which is easy to find, available, but temperature-sensitive
• 1947: Transistor discovery
• 1954: First silicon transistor due to less temperature sensitivity and abundance.
• 1970: Development of GaAs transistor for increased speed (5X of Si) but more expensive

Silicon (Si)

• It is, after oxygen, the most abundant element on Earth, comprising 25.7% of earth's crust
• Refining issues initially hindered its use in devices.
• Isolated silicon atoms have 14 protons and electrons.

Germanium (Ge)

• It is a semiconductor material however Silicon replaced it due to excessive reverse current.

Galium Arsenide (GaAs)

• It is used in semiconductors for solar cells and lasers.

Silicon Crystal

• Silicon atoms arrange into a crystal structure, sharing electrons with four neighbors to achieve eight valence electrons.
• Valence electrons create covalent bonds, giving the crystal solidity.
• Hydrogen can form polar or nonpolar covalent bonds, sharing electrons evenly or unevenly depending on the other element in the bond.
• Each silicon atom in a crystal has eight valence electrons, which provides chemical stability, resulting in a solid silicon material.
• Valence Saturation occurs with eight electrons and no room for more.

Free Electron and Hole

• Ambient temperature is the temperature surrounding silicon material.
• Heat from ambient temperatures above absolute zero (-273 °C) causes vibrations in the silicon crystal.
• Vibrating atoms can dislodge electrons into a larger orbit, creating a free electron.
• The departure of the electron creates a hole, which behaves like a positive ion and attracts other electrons.

Semiconductor Classification

• Intrinsic semiconductors are in their purest form, like a silicon crystal with only silicon atoms.
• Extrinsic semiconductors have other atoms (impurities) mixed in.

Doping

• It is used to increase electron or hole concentration.
• Donors (Column V elements) add more electrons.
• Examples: Phosphorus (P), Arsenic (As), Antimony (Sb)
• Acceptors (Column III elements) add more holes.
• Examples: Boron (B), Gallium (Ga), Indium (In), Aluminum (Al)

Impurities

• Doping a silicon crystal with a pentavalent impurity like Arsenic (As) provides an extra electron that is not needed in covalent bonding, enabling it to float as a free electron.
• Boron, (B) for example, is a trivalent impurity creates the need for one more valence electron at the location in the crystal to maximize the electrical stability.

Types of Material

• Aluminum (Al), Boron (B) or gallium (Ga) are some other trivalent impurities used to maximize stability.

N and P Type Material

• A diode is made by joining p- and n-type semiconductor materials.

PN Junction Diode

• Doped regions meet to form a p-n junction.
• Diodes are unidirectional devices.
• The semiconductor diode made from N and P type materials is in many applications

Effects

• Free electrons in the n-side fall into holes, which are on the p side, creating ions.
• Electrons leaving the n side and falling into the p-side cause a positive ion on the n-side, and a negative ion on the p-side
• Each dipole has an electric field
• Barrier potential is 0.3 V for Germanium and 0.7 V for Silicon.
• Practical uses include rectifiers

Rectifiers

• An electrical device converting alternating current (AC) to direct current (DC) (i.e. mobile phones).
• A circuit of diodes create DC out of AC
• The conversion process is rectification.

Light Emitting Diodes (LEDs)

• It is a semiconductor light source, LEDs also used as indicator lamps and for lighting.
• Use in aviation, automotive advertising, signals, displays, video, and sensors
• Infrared LEDs are in remote controls.

Photodiodes

• Capable of changing light into current or voltage
• Traditional solar cells are a photodiode with large power area

Applications

• Use: disc players, smoke detectors, infrared remote controls.
• Symbol indicated palooob/papasok
• Reverse Biased
• Light is focused through a glass lens on the junction.
• Increased light intensity generates more electron pairs and increases the photocurrent

Bottle Counting Plant

• A light beam is always focused continuously on the photodiode.
• When a bottle passes, a light is interrupted, thus, photocurrent reduces to zero, and the number of bottles is counted

Optocoupler

• An opto-isolator transfers electrical signals by using light waves, which provides electrical isolation.
• It also prevents high or rapidly changing voltages from damaging components.
• Transistor (phototransistor), alternating or directed current used to block or isolate voltages, including electrostatic discharge

LASER DIODE

• Active medium is a semiconductor similar to that found in a light-emitting diode
• The most common type of laser diode is formed from a p-n junction

LASER DIODE – VIDEO

• Used for signal transmission in fiber optics
• Fiber Optics converts electrons into a signal rather than copper wire and is made from glass

Biasing

• A controlling voltage/current is driven into a diode, determining the amount of the energy load.
• Battery voltage pushes electrons to the depletion layer.
• A voltage source below knee voltage (barrier potential) will not enter the deletion layer.
• Supplying a higher voltage than the knee voltage permits free electrons to freely combine with holes for continued current through the diode.
• If overcoming DELPLETION REGION VOLTAGE is overcome, transferring electrons happens more readily to the active side of the material
• A battery’s passive terminal connects directly to the p-type area, while a negative terminal connects directed to the n-type area.
• forward-Bias Condition (VD > 0 V)
• The magnitude must be greater than 0 so voltage force can push the active components onto the far side.

Conditions

• Applying a positive charge on the positive side and negative on the negative side triggers this.
• Depletion shrinks as electrons jump to the other.
• Electron in n-recombines holes of p-type & ions become boundary reducing range of depletion.

Application

• Potential VD “pressures” n-type electrons holes into the recombination near boundary ions, which less width in depletion.
• Increased bias magnitude causes less deployment width, thus more electrons flow across the joint at once, causing exponential incline.

Reverse Bias

• Negative attracts +, vice-versa
• Range of space increases
• No current flow
• It remains closed.
• reverse-Bias Condition (VD < 0 V)
• Must be smaller than zero
• Exterior voltage that causes it connect to the side where holes are pushed in, and electrons get pushed to the battery and make the range of field larger between the space & battery.
• If electrons are there, they’ll combine to battery’s side creating a field from negative to positive by the battery.

Zero Bias

• Diode is just connected, doesn’t source voltages.

No Applied Bias V=V)

• In fact, two materials combine (joins).
• Not enough freedom inside there.
• IT REMAINS IN THE SIDE with which it began

Diode Polarity

• Diodes Have Polarity
• Must arrange properly

DIODE VOLT-AMPERE CHARACTERISTIC CURVE

• Forward Region voltage/current = is a forward-bias
• REVERSE REGION is a reverse-bias
• KNEE VOLTAGE is the barrier potential that needs meeting
• It is about 0.7 for Silicon, or 0.3 for Germanium
• F: Diode conducts easily • R<the diode cannot conduct BULK RESISTANCE

Diode approximations

• The first approximation: FOR TROUBLESHOOTING (TECHNICIAN LEVEL).
• The second approximation: EASY SOLUTION (ENGINEERING LEVEL).
• The third approximation: MORE ACCURATE SOLUTION.

Three Diode models

• The best is the LINEAR EQUIVALENT
• The straight line portions do not make it similar & segments are very close by
• The standard ac resistance specifies level, then ON state shows.
• If the diode isn’t directed through this approach, it will result inside the open-circuit to that diode

Biasing

• The expression is based on voltage that is regulated.

PIECEWISE-LINEAR EQUIVALENT CIRCUIT

• This simulates the properties of an electrode/diode arrangement as it makes linear sections. The level roughly is at a level of specified functions
• Such: by the functions we know silicon must move 0.7V for a certain shift

Simplified Equivalent Circuit I

• It is under the condition that’s little enough & elements get ignored
• It is frequently in circuit testing.
• It says that a forward-biased diode is electronic around the 0.7 drop level to state ratings

IDEAL EQUIVALENT CIRCUIT

• Almost all functions are too little & can get ignore
• An isolated signal in diode is dependent on level of intensity which the connection is at

Diodes

• Diode must have maximums ratings/features
• Its standard is Voltage ratings or current (maximums)
• Exceeding it can be the result of permanent failures.