Semiconductors: Silicon vs. Germanium properties

Diodes

• Diodes allow current to flow in one direction only.
• Diodes are like check valves for electrons.

Semiconductor Materials

• All materials comprise atoms and atoms properties dictate electrical conductivity.
• Atoms consist of a valence shell, inner shells and a nucleus.
• A carbon atom contains four valence shell electrons and two inner shell electrons.
• The nucleus contains six protons and six neutrons so the +6 indicates the positive charge of the six protons.
• A core's net charge is +4 due to a +6 nucleus and -2 inner-shell electrons.

Conductors

• Conductors easily facilitate the flow of electrical current.
• The best conductors are single-element materials like copper, silver, gold, and aluminum
• Conductors have atoms characterized by one loosely bound valence electron.
• These valence electrons easily break free, becoming free electrons that make up current when moving uniformly.

Insulators

• Insulators do not conduct electrical current under normal conditions.
• Insulators are typically compounds rather than single-element materials.
• Valence electrons in insulators are tightly bound with very few free electrons.

Semiconductors

• Semiconductors have a conductivity between conductors and insulators.
• Pure semiconductors are neither good conductors nor good insulators.
• Common semiconductors include silicon, germanium, and carbon.
• Compound semiconductors like gallium arsenide exist.
• Single-element semiconductors atoms feature four valence electrons.

Semiconductor Atom vs Conductor Atom. Silicon vs. Copper

• Silicon's net core charge is +4 (14 protons - 10 electrons)
• Copper's net core charge is +1 (29 protons - 28 electrons).
• Copper's valence electrons experience an attractive force of +1
• Silicon's valence electrons experience an attractive force of +4
• There is four times greater force holding valence electrons to silicon atoms than to copper atoms given these values. This means the valence electron in copper has less binding force and more energy than in silicon, thus it can escape its atoms easier.

Silicon and Germanium

• Silicon and germanium are both semiconductors having four valence electrons.
• Silicon is the most commonly used semiconductor material for diodes, transistors and integrated circuits.
• Germanium's valence electrons are in the fourth shell while silicon's are in the third shell.
• Germanium valence electrons has higher energy levels, needing a smaller amount of additional energy to escape the atom.
• Germanium is less stable at high temperatures; silicon is the most widely used semiconductive material overall.

Covalent Bonds

• Each silicon atom forms a silicon crystal by positioning itself with four adjacent silicon atoms.
• A silicon atom shares an electron with each of its four neighbors creating eight valence electrons per atom for chemical stability.
• Electron sharing forms covalent bonds holding atoms together with shared electrons attracted to two adjacent atoms equally.
• Covalent bonding in intrinsic silicon crystals involves no impurities.
• Germanium also exhibits similar covalent bonding because it has four valence electrons too.

Conduction Electrons and Holes

• Electron-hole pairs exist in silicon crystals.
• Free electrons are continuously generated, while some recombine with holes.

N-Type and P-Type Semiconductors

• Semi-conductive materials do not conduct current well and are of limited value in their intrinsic state because of the limited number of free electrons and holes..
• Intrinsic silicon (or germanium) should be modified by increasing the number of free electrons and holes to increase its conductivity.
• This achieved by the addition of impurities to the intrinsic material.
• There are two extrinsic (impure) semi-conductive material types:
  • N-type
  • P-type
• They are key building blocks for electronic devices.

Doping Semiconductors

• Doping is the process of drastically increasing the conductivity of silicon or germanium by adding impurities.
• Doping increases the number of current carriers (electrons or holes).
• The two categories of impurities are N-type and P-type.

N-Type Semiconductors

• Pentavalent impurity atoms are added to increase conduction band electrons in intrinsic silicon
• Arsenic (As), phosphorus (P), bismuth (Bi) & antimony (Sb) are atoms with five valence electrons
• Pentavalent atoms (like antimony) form covalent bonds with four silicon atoms.
• A donor atom's valence electrons form covalent bonds with silicon atoms, which leaves one extra electron. This extra electron becomes a conduction electron.
• The number of conduction electrons is accurately controlled by the number of impurity atoms added to silicon plus, the conduction electron doesn't leave a valence band hole

Majority and Minority Carriers

• Silicon or germanium doped with pentavalent atoms becomes an N-type semiconductor because most carriers are electrons.
• 'N' indicates negative charge on an electron.
• In N-type material, electrons are the majority carriers, holes are minority carriers.

P-Type Semiconductors

• Trivalent impurity atoms are added to increase holes in intrinsic silicon
• Boron (B), indium (In), and gallium (Ga) are atoms with three valence electrons.
• Trivalent atoms (like boron) form covalent bonds with four adjacent silicon atoms.
• Since 4 electrons are required, a hole occurs when each trivalent atom is added,
• Trivalent atoms can take an electron and are often referred to as an acceptor atom.
• Control the number of holes by carefully controlling the number of trivalent atoms added to silicon.

Majority and Minority Carriers in P-Type Semiconductors

• Silicon/germanium doped using trivalent atoms is a P-type semiconductor, since most carriers are holes.
• Holes have positive charges, because the electron's absence leaves a net positive charge on the atom.
• Holes are majority carriers in P-type material, whereas electrons are minority carriers

P-Type and N-Type Materials

• P-type materials have boron adding holes when bonding with silicon atoms with equal protons and electrons, so there is no net charge in the material.
• N-type silicon materials have antimony releasing electrons when bonding with four silicon atoms with equal protons and electrons (free electrons), so there is no net charge in the material.

Diode Symbols, Cathode and Anode

• Diodes in circuit diagrams use the following conventions:
  • The cathode (negative) side looks like a K
  • The anode (positive) side looks like an 'A' on its side.
• Current flows when a cathode connects with a negative source.

PN Junctions

• Diodes are created when a section of intrinsic silicon is doped with N-type, and another part is doped with P-type material, forming a PN junction.
• The P region has many holes (majority carriers) from impurity atoms and few thermally generated free electrons (minority carriers).
• The N region has many free electrons (majority carriers) from impurity atoms and few thermally generated holes (minority carriers).
• Free electrons in the N region drift randomly in all directions and diffuse across a PN junction to combine with P region holes.

Depletion Region Formation

• N region losses free electrons upon PN junction formation as they diffuse and create positive charges near the junction.
• P region losses holes as electrons move in, creating negative charges; a positive and negative charge layer forms a depletion region

PN Junction after Electron Surge

• After electrons initially surge across a PN junction, the depletion region expands and equilibrium is established.
• This prevents further electron diffusion across the function.

Barrier Potential

• The depletion region contains positive and negative charges on opposite sides of the PN junction.
• Forces form between opposite charges and these form an electric field.
• An electric field acts as a barrier for free electrons in the N region, so energy must be expended to move an electron and for electrons to move across an electric field's barrier in the depletion region.
• Barrier potential is the electric field's potential difference across the depletion region, requiring voltage to move electrons.
• A PN junction's barrier potential is affected by semi-conductive material, and the typical typical barrier potential is around 0.7 volts for silicon, or 0.3 volts for germanium.

Forward Bias

• Applying DC voltage can forward bias a diode
• Forward bias allows current through a PN junction.
• In this situation, connect the negative side of the VBIAS to the N region of the diode, and the positive side to the P region.
• When a N region conduction-band conducts push towards the PN junction, the P region also pushes towards the junction to repel like charges.
• When external voltage overcomes barrier potential it provides N region electrons with sufficient energy to penetrate and cross the depletion region.
• Electrons combine with the P region holes.
• Electron flow from the -VE supply increases as electrons leave N region.
• N-region current means the conduction of electrons (majority carriers) towards junction
• Conduction electrons entering the P region combine with holes, becoming valence electrons.
• Afterwards, valence electrons then move as valence electrons from hole-to-hole near the positive voltage source.
• Current in the P region equals the movement of a holes (majority carriers) through space leading to the the junction.

Forward Bias Effect on Depletion Region

• As more electrons flow are introduced to the depletion region, the positive ions are reduced.
• As more holes flow into the depletion region, the number of negative ions is simultaneously reduced.
• Reduction of ions causes the depletion region to narrow.

PN Junction Forward Bias

• Forward bias happens with a +ve anode and a -ve cathode.
• Current will flow when the barrier potential is overcome.

Reverse Bias

• Reverse bias prevents current through a diode.
• Connect the positive VBIAS with the N region and the negative to the P region
• The Depletion region is wider than in forward bias here.
• The positive side pulls electrons (majority carriers) in the N region from the PN junction and creates additional positive sides
• The electrons from the negative source enters the as valence electrons that leave additional negative ions.
• Both these effect result in depletion region widening/minority carrier depletion.
• Flow of valence electrons can mean "pulled" holes lead towards the positive side but the initial flow of charge carriers only lasts for a very short time

Reverse Bias and Charge Carriers

• The initial flow of charge carriers in reverse bias is only transient but the availability of majority carriers decreases as depletion region widens.
• The N and P regions can be depleted of majority carriers and as this occurs, the electric field will increase. This occurs until the potential equals bias voltage VBIAS.
• Transition current will cease, except for small reverse current.

Reverse Leakage Current

• Very small leakage current (IR) is produced by minority carriers during reverse bias.
• Because the depletion region contains a small amount of thermally produced electron-hole pairs ,some electrons diffuse across the PN junction before recombination.
• This process establishes a small minority carrier current through the material.

Reverse Current Facts

• The reverse current (IR) is primarily affected by junction temperature and not the amount of reverse bias voltage.
• Rising temperature increases leakages while Germanium sees greater leakage current levels versus silicon.

Reverse Breakdown

• The reverse current will drastically increase if the bias voltage is increased to a specific value. This specific voltage can be called the 'breakdown voltage'.
• The free minority electrons energy increase due to high voltage and these now high energy speeding through P region.
• The high energy collides knocks out valence electrons and are pulled into the conduction band.
• Creates high energy conduction electrons that trigger this process again
• When one election knocks only two others, avalanche occurs and creates a very high that can damage the diode.

V-I Characteristics: Forward Bias

• No forward current happens with 0 diode voltage.
• Increase the forward-bias, and forwards move in alignment with the forward voltage.
• Part of the foward-bias voltage drops through the resistance to help limit current
• Around 0.7 V of forward bias, current increases rapidly and the Voltage across the increases above 0.7 V.

V-I Characteristics: Diodes

• Increasing the forward voltage forward bias causes faster current increase. The internal dynamic resistance can affect this diodes voltage The graph of the above shows:
  • The diode forward voltage (VF) increases to the right along the horizontal axis.
  • The forward current (I℉) increases upward along the vertical axis
• Forward current increases only a small bit until the PN's forward voltage goes approximately 0.7V (knee on the curve)
• V(f) goes over 0.7 when the current increasing are mainly due to the dynamic resistance's voltage drop.

Dynamic Resistance

• Forward biased diodes dont have resistance
• Because resistance varies along V-I lines, its dynamic or AC resistance can be identified
• Under the knee on the curve you can identify the very little increases in the voltage. The resistance starts in knee area on the curve.
• After this it then bottoms out when there is a big chwnge in voltage.

V-I Characteristics: Reverse Bias

• When you apply reverse base diodes, minimal reverse current (Ir) and increase slowly voltage across the diodes which applies when breakdown happens.

V-I Characteristics Overall

• This combined creates overall a great voltage graph for diodes.
• (I) ℉ scale is in mA and (I)r is in micro-Amps..

Temperature Effects on V-I Characteristcs

• A forward based diode, will act as follows with raised temperatures.
• Temp increases -Forwards current in total increase.
• A high diode with raise temp the more the reverse current

Diode Structure and Symbol

• A diode is a single PN junction device.
• With metal contacts and wire leads
• The parts: An N-type and P-type semiconductor.
• A general-purpose or rectifier diode:
  • Where P region = Anode and N region = Cathode
• Current direction is opposite electron flow

Diode Connections: Forward Bias

• A diode has a forward-bias with voltage as follows:
  • The source is connected to the anode a current-limiting resistor -The negative source is connected to the cathode. -Forward-biased current moves from cathode to anode. The diode has barrier potentia which cause forward-bias current from positive at the anode to negative at the cathode

Diode Connections: Reverse Bias

• A Diode is reverse-biased with voltage source as follows:
  • Negative terminal is connected to the anode circuit side.
  • Positive terminal is connected to the cathode side.
  • Reverse current is negligible.
  • The bias voltage is across the diodes

Ideal Diode Models

• It's basically a switch
  • Forward-biased = Closed (on) switch
  • Reverse-biased = Open (Off) switch
• Barrier potential, dynamic resistance and reverse current is neglected.

Ideal V-I Characteristics

• The characteristic curve is a graphical plot Depicts an ideal diode operating. Which means the :
  • Barrier potential and forward dynamic resistance are neglected
  • The diode is assumed to have a zero voltage across.

Practical Diode model

• The practical model adds the barrier potential to the ideal switch model with the voltage = 0.7V
• A closed/small equivalent of voltage that equals to =0 will forward bias.
• An open equivalent when reverse base diodes are in the deal model.

Practical Characteristics

• the diode is assumed to be voltage, and is found the curve in indication the position of where the voltage originates.

The Complete Diode Model

• A completed diodes contain barrier potential with both small dynamics and internal resistance.
• Forward or reverse base diodes act in internal dynamics.

Typical Diodes

• The anodes and cathodes on diodes are indicated in several ways:
  • A band
  • A tab
  • Other feature
• Packages in a case one line is connected the case is the cathode.

Rectifier Diodes

The term ""diode"" and ""rectifier"" are often used interchangeably, but they're not the same

• Diodes are small circuits where current typically measure in milliamp range.
• Rectifier a small amounts
• The primary use for rectification: 100 Amp or greater.
• Primary use with all rectifier includes" Half wave,Full wave, Dc Blocker"

Diodes in series Half Wave Rectifiers

• Load acts as a one way
  • Currents flows one way.
  • The AC becomes forwarded through cycle.
  • Is accomplished

Half Wave Rectifiers

• When in parallel half circuit with all components including, diodes ac source, load all of this can effect, effect,
• Will short each earth results .

Full Wave rectifiers

With each Diodes Applied, and what has occurred, When reverse is biassed in the, reverse is bias or, is biassed through it all. To, DC is achieved, in total

Diodes in "Series with a bridge"

• all 4 diodes are used in, EMF Bridge

• A Bridge rectifiers contains 2 simultatiously

• The current flow are doubled with series.

Series Connected Diodes

• the combined all have effects as a result. the increase creates ability
• When forwarding bias or reverse. there will be voltage drops in the diodes
• High resistance will be connected due to the increased
• High resistance will be in protected areas.

Parallel Connected diodes

• connecting with increase with increase
• with proper characteristics is, there will also exist.
• However that is not all that possible to perform, and not that simply done.

Parallel with rectifcation

• You need "A" amounts of rectifiers with rectifier with a resistance. you will needed amounts and numbers with ohms.

The DMM Diode Test Position

• Digital multi-tool has test functions
• Is set and tested -The meter has internal settings
• Voltage readings shown under, the function.

Working diodes

• positive is connector to the . Anode , and negative is connector to the , cathode will forward diodes, the result readings will be between a voltage to about" ".volts
• For a result there will always have the ability to generate high "reverse resistance". And high" voltage" is the result.

Diode Testing and Faults (Defective Diode)

• If a diode is ""open"" "" you will get an open circuit with very voltages
• If a diodes is shorted, the metter will also read ""0""" ( 0V "in both)
• If ""Ohm"" function is set : Set to ""OHM" resistance on all Red for the ''anode " and" black"" To ""CATHODES" ""

Diode Biasing Summary

• There is are some ways to tell the difference and the properties which include "Forward Bias" " Majority-carrier Current"" Positive / Negative N regions" and ""Voltages" has to be greater" than the barrier

Light Emitting Diode (LED)

• These is are types, LED.
• when these happen with +P region + "Light Energy", It with reverse with all types