1. Electronic workshop Dr. Imtiaz Hussain email: imtiaz.hussain@faculty.muet.edu.pkimtiaz.hussain@faculty.muet.edu.pk URL :http://imtiazhussainkalwar.weebly.com/ Lecture-7 Diodes and Transistors

2. Semiconductor Diodes Diode is constructed by fusing two different types of doped semiconductors (P-type and N-type) together.

3. What Are Diodes Made Out Of? Silicon (Si) and Germanium (Ge) are the two most common single elements that are used to make Diodes. Silicon and Germanium are both group 4 elements, meaning they have 4 valence electrons. Their structure allows them to grow in a shape called the diamond lattice. In diamond lattice lattice, each atom shares its valence electrons with its four closest neighbors. This sharing of electrons is what ultimately allows diodes to be build. When dopants from groups 3 or 5 (in most cases) are added to Si or Ge it changes the properties of the material so we are able to make the P- and N-type materials that become the diode. Si +4 Si +4 Si +4 Si +4 Si +4 Si +4 Si +4 Si +4 Si +4

4. N-Type Material When extra valence electrons are introduced into a material such as silicon an n-type material is produced. The extra valence electrons are introduced by putting impurities or dopants into the silicon. The dopants used to create an n-type material are Group V elements. The most commonly used dopants from Group V are arsenic, antimony and phosphorus.. The 2D diagram to the left shows the extra electron that will be present when a Group V dopant is introduced to a material such as silicon. This extra electron is very mobile. +4 +5 +4

5. P-Type Material P-type material is produced when the dopant that is introduced is from Group III. Group III elements have only 3 valence electrons and therefore there is an electron missing. This creates a hole (h+), or a positive charge that can move around in the material. Commonly used Group III dopants are aluminum, boron, and gallium. The 2D diagram to the left shows the hole that will be present when a Group III dopant is introduced to a material such as silicon. This hole is quite mobile in the same way the extra electron is mobile in a n-type material. +4 +3 +4

6. What Are Diodes Made Out Of? Silicon (Si) and Germanium (Ge) are the two most common single elements that are used to make Diodes. Gallium is a group 3 element while Arsenide is a group 5 element. When put together as a compound, GaAs creates a zincblend lattice structure. In zincblend lattice, each atom shares its valence electrons with its four closest neighbors. This sharing of electrons is what ultimately allows diodes to be build. When dopants from groups 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 make the P- and N-type materials that become the diode. Si +4 Si +4 Si +4 Si +4 Si +4 Si +4 Si +4 Si +4 Si +4

7. Diode Terminals

9. Diode Biasing Open Circuit Short Circuit Forward Biased Diode Reverse Biased Diode

10. Light Emitting Diode (LED) A compound that is commonly used for LEDs construction is Gallium Arsenide (GaAs), because of it’s large bandgap. Gallium is a group 3 element while Arsenide is a group 5 element. When put together as a compound, GaAs creates a zincblend lattice structure.

11. Light Emitting Diode (LED)

12. Task#1 S. N.oModelVoltageImplication Reverse BiasForward Bias 1. 2. 3. 4. 5. Take few diodes and check it using multimeter’s continuity function and fill in the following table.

13. Task#2 Take few LEDs and check it using the same method as task#1 and fill in the following table. S. N.oColorOn/OffImplication Reverse BiasForward Bias 1. 2. 3. 4. 5.

14. Transistor A transistor is a 3 terminal device that is used in a variety of applications such as amplification and switching. There are two types of transistors categorized according to their construction: – Bipolar Junction Transistor (BJT) – Field Effect Transistor (FET)

15. BJT The Bipolar Junction Transistor (BJT) comes in two flavors

16. FET It is a two layer three terminal device made up of two pieces of semiconductors. Like the BJT, this comes in two flavors too

17. Task#3 S N.oTerminals of the BJT Type of Transistor NPN/PNP Implication ABC 1. 2. 3. 4. 5.

18. END OF LECTURE-7 To download this lecture visit http://imtiazhussainkalwar.weebly.com/