Course: ETE 107 Electronics 1 Course Instructor: Rashedul Islam Lecture # 01 Course: ETE 107 Electronics 1 Course Instructor: Rashedul Islam

Outlines: Introduction to Electronics, Voltage, Current, Resistance & Power Conductors, Insulators & Semiconductors Intrinsic & Extrinsic Semiconductors P Type & N Type Semiconductor Materials, P-N Junctions Operational Principle of P-N Junction Diode Forward & Reverse Bias

What is Electronics: Electronics is the division of science, engineering & technology that deals with electronic components, their characteristics and operational methods. Examples of Electronic Components are: Diodes, Transistors, Amplifiers and many more semiconductor devices.

Voltage, Current, Resistance & Power: Voltage is the pressure/force which causes the electrons to be moved. The Unit for measuring the Voltage is Volt. Current is the result/output of the movement or flow of Electrons. The unit for measuring the current is Ampere. Resistance is the ability of opposing the flow of Electrons (Current). It is measured in Ohm. Lastly, Power is the multiplication of Voltage & Current. That means Power is the rate in which electric energy transferred in any electric circuit. The unit of Power measurement is Watt.

Conductor: A Conductor is a material which contains movable electronic charges. Here, electronic charges can be either positive charge (e.g. Holes) or negative charge (e.g. Electrons). Inside a Conductor a free electronic charge can move freely and thus provides us Electronic Current. The term conductor is also used interchangeably for indicating Wires. Example: Copper, Aluminum etc.

Insulator: Semiconductor: An Insulator is a material which contains very strongly bonded electrons with nuclear in atoms and does not have any free electrons to move Opposite characteristics than that of a conductor Example: Glass, Wood, Plastic etc. Semiconductor: Semiconductors are materials which has electrical conductivity intermediate between Conductor & Insulator. In normal condition, it acts like an Insulator. But its conductivity varies in Temperature, Optical Excitations or Impurity contents. It non-linear Current-Voltage Characteristics Free electronic Charges means the charges that are not bound in an atom or can be pulled out from an atom easily. Flow of Current is always the opposite of flow of Electrons

Intrinsic & Extrinsic Semiconductors: A perfect semiconductor material with no impurities or lattice defects is called an Intrinsic Semiconductor material. Examples: Pure Silicon, Gallium Arsenide. On the other hand a semiconductor material in which impurities has been put-in intentionally is called an Extrinsic Semiconductor Material. Examples: P-Type & N-Type Semiconductors. The Process of putting impurities inside an intrinsic semiconductor is called Doping.

P-Type Semiconductors: Whenever by doing Doping process, positive electrical charge is increased in a pure semiconductor device, it is then called P-Type Semiconductors. Group III elements (e.g. Boron, gallium) in periodic tables are used for making P-type semiconductors N-Type Semiconductors: Whenever by doing Doping process, negative electrical charge is increased in a pure semiconductor device, it is then called N-Type Semiconductors. Group V elements (e.g. Phosphorus, Arsenic) in periodic tables are used for making P-type semiconductors

P-N Junctions: When a junction of P-type & N-type material is created in a single crystal semiconductor materials, it is called P-N Junction. Different Processes such as ION Implantation, Diffusion, Doping are used to create P-N Junctions. P–N junctions are elementary "building blocks" of many semiconductor electronic devices such as diodes, transistors, solar cells, LEDs, and integrated circuits;

Operational Principle of P-N Junction Diode To understand how a pn-junction diode works, begin by imagining two separate bits of semiconductor, one n-type, the other p-type Bring them together and join them to make one piece of semiconductor

Operational Principle of P-N Junction Diode Free electrons on the n-side and free holes on the p-side can initially wander across the junction. When a free electron meets a free hole it can 'drop into it'. So far as charge movements are concerned this means the hole and electron cancel each other and vanish.

Operational Principle of P-N Junction Diode As a result, the free electrons and holes near the junction tend to eat each other, producing a region depleted of any moving charges. This creates what is called the depletion zone.

Operational Principle of P-N Junction Diode Now, any free charge which wanders into the depletion zone finds itself in a region with no other free charges. Locally it sees a lot of positive charges (the donor atoms) on the n-type side and a lot of negative charges (the acceptor atoms) on the p-type side. These exert a force on the free charge, driving it back to its 'own side' of the junction away from the depletion zone.

Operational Principle of P-N Junction Diode The acceptor and donor atoms are 'nailed down' in the solid and cannot move around. However, the negative charge of the acceptor's extra electron and the positive charge of the donor's extra proton (exposed by it's missing electron) tend to keep the depletion zone swept clean of free charges once the zone has formed. A free charge now requires some extra energy to overcome the forces from the donor/acceptor atoms to be able to cross the zone. The junction therefore acts like a barrier, blocking any charge flow (current) across the barrier.

Forward & Reverse Bias: An external voltage applied to a PN junction is called BIAS. If, for example, a battery is used to supply bias to a PN junction and is connected so that its voltage opposes the junction field, it will reduce the junction barrier and, therefore, aid current flow through the junction. This type of bias is known as forward bias, and it causes the junction to offer only minimum resistance to the flow of current. If the battery mentioned earlier is connected across the junction so that its voltage aids the junction, it will increase the junction barrier and thereby offer a high resistance to the current flow through the junction. This type of bias is known as reverse bias