PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Kristin Ackerson, Virginia Tech EEKristin Ackerson, Virginia Tech EESpring 2002Spring 2002Table of ContentsTable of ContentsKristin Ackerson, Virginia Tech EEKristin Ackerson, Virginia Tech EESpring 2002Spring 2002What are diodes made out of?____________________slide 3What are diodes made out of?____________________slide 3N-type material_________________________________slide 4N-type material_________________________________slide 4P-type material_________________________________slide 5P-type material_________________________________slide 5The pn junction_________________________________slides 6-7The pn junction_________________________________slides 6-7The biased pn junction___________________________slides 8-9The biased pn junction___________________________slides 8-9Properties of diodes_____________________________slides 10-11Properties of diodes_____________________________slides 10-11Diode Circuit Models ____________________________slides 12-16Diode Circuit Models ____________________________slides 12-16The Q Point____________________________________slides 17-18The Q Point____________________________________slides 17-18Dynamic Resistance_____________________________slides 19-20Dynamic Resistance_____________________________slides 19-20Types of diodes and their uses ___________________ slides 21-24Types of diodes and their uses ___________________ slides 21-24Sources_______________________________________slide 25Sources_______________________________________slide 25What Are Diodes Made Out Of?What Are Diodes Made Out Of?Kristin Ackerson, Virginia Tech EEKristin Ackerson, Virginia Tech EESpring 2002Spring 2002•Silicon (Si) and Germanium (Ge) are the two most Silicon (Si) and Germanium (Ge) are the two most common single elements that are used to make Diodes. common single elements that are used to make Diodes. A compound that is commonly used is Gallium A compound that is commonly used is Gallium Arsenide (GaAs), especially in the case of LEDs Arsenide (GaAs), especially in the case of LEDs because of it’s large bandgap. because of it’s large bandgap. •Silicon and Germanium are both group 4 elements, Silicon and Germanium are both group 4 elements, meaning they have 4 valence electrons. Their meaning they have 4 valence electrons. Their structure allows them to grow in a shape called the structure allows them to grow in a shape called the diamond lattice.diamond lattice.•Gallium is a group 3 element while Arsenide is a group Gallium is a group 3 element while Arsenide is a group 5 element. When put together as a compound, GaAs 5 element. When put together as a compound, GaAs creates a zincblend lattice structure.creates a zincblend lattice structure.•In both the diamond lattice and zincblend lattice, each In both the diamond lattice and zincblend lattice, each atom shares its valence electrons with its four closest atom shares its valence electrons with its four closest neighbors. This sharing of electrons is what ultimately neighbors. This sharing of electrons is what ultimately allows diodes to be build. When dopants from groups allows diodes to be build. When dopants from groups 3 or 5 (in most cases) are added to Si, Ge or GaAs it 3 or 5 (in most cases) are added to Si, Ge or GaAs it changes the properties of the material so we are able to changes the properties of the material so we are able to make the P- and N-type materials that become the make the P- and N-type materials that become the diode.diode.SiSi+4+4SiSi+4+4SiSi+4+4Si Si +4+4SiSi+4+4SiSi+4+4SiSi+4+4SiSi+4+4SiSi+4+4The diagram above shows the The diagram above shows the 2D structure of the Si crystal. 2D structure of the Si crystal. The light green lines The light green lines represent the electronic represent the electronic bonds made when the bonds made when the valence electrons are shared. valence electrons are shared. Each Si atom shares one Each Si atom shares one electron with each of its four electron with each of its four closest neighbors so that its closest neighbors so that its valence band will have a full 8 valence band will have a full 8 electrons.electrons.N-Type MaterialN-Type MaterialKristin Ackerson, Virginia Tech EEKristin Ackerson, Virginia Tech EESpring 2002Spring 2002N-Type Material:N-Type Material:When extra valence electrons are introduced When extra valence electrons are introduced into a material such as silicon an n-type into a material such as silicon an n-type material is produced. The extra valence material is produced. The extra valence electrons are introduced by putting electrons are introduced by putting impurities or dopants into the silicon. The impurities or dopants into the silicon. The dopants used to create an n-type material dopants used to create an n-type material are Group V elements. The most commonly are Group V elements. The most commonly used dopants from Group V are arsenic, used dopants from Group V are arsenic, antimony and phosphorus. antimony and phosphorus. The 2D diagram to the left shows the extra The 2D diagram to the left shows the extra electron that will be present when a Group V electron that will be present when a Group V dopant is introduced to a material such as dopant is introduced to a material such as silicon. This extra electron is very mobile. silicon. This extra electron is very mobile. +4+4+4+4+5+5+4+4+4+4+4+4+4+4+4+4+4+4P-Type MaterialP-Type MaterialKristin Ackerson, Virginia Tech EEKristin Ackerson, Virginia Tech EESpring 2002Spring 2002P-Type Material:P-Type Material:P-type material is produced when the dopant P-type material is produced when the dopant that is introduced is from Group III. Group that is introduced is from Group III. Group III elements have only 3 valence electrons III elements have only 3 valence electrons and therefore there is an electron missing. and therefore there is an electron missing. This creates a hole (h+), or a positive charge This creates a hole (h+), or a positive charge that can move around in the material. that can move around in the material. Commonly used Group III dopants are Commonly used Group III dopants are aluminum, boron, and gallium.aluminum, boron, and gallium.The 2D diagram to the left shows the hole The 2D diagram to the left