Diodes A diode is an electrical device allowing current to move through one direction also unidirectional current property. Semiconductor materials are commonly used to design this device. Semiconductors like silicon (Si), germanium (Ge) and a compound gallium arsenide (GaAs). There are types of diodes designed for different functions and natural usage.a) Backward Diode- Also known as back diode- Variation on a zener diode or tunnel diode having a better conduction for small reverse biases than for forward bias voltages. SCHEMATIC SYMBOL FOR BACKWARD DIODEb) BARITT Diode- Short term for Barrier Injection Transit Time diode- Used in microwave signal generation- Very similar to IMPATT but the main difference is that it uses thermionic emission rather than avalanche multiplicationc) Gunn Diode- A PN junction diode- Used for producing microwave signals PICTURE OF A GUNN DIODEd) Laser Diode- Generates coherent light- Used in many applications like DVDs, CD drives and laser light pointers. PICTURE OF A LASER DIODEe) Light Emitting Diode (LED)- When the diode is connected in forwarding bias, current flows through the junction and generates the light. SCHEMATIC SYMBOL FOR LEDsf) Photodiode- Used to detect light- When light strikes a PN-junction it can create electrons and holes SCHEMATIC SYMBOL FOR PHOTODIODEg) PIN Diode- Has the standard P-type and N-type regions, but the area between the two regions (Intrinsic semiconductor) has no doping- Intrinsic semiconductior has the effect of increasing the area of the depletion region which can be beneficial for switching applications. PICTURE OF PIN DIODE PN JUNCTION OF THE DIODEh) Schottky Diode- Has lower forward voltage drop than ordinary silicon PN-junction diodes- Extensively used in rectifier application, clamping diodes and also in Radio Frequency application SCHEMATIC DIAGRAM FOR SCHOTTKY DIODEi) Step Recovery Diode- Type of microwave diode used to generate pulses at very High Frequency (HF).- Depend on the diode which has a very fast turn-off characteristic for their operation. SCHEMATIC SYMBOL FOR STEP RECOVERY DIODEj) Tunnel Diode- Also known as “Esaki diode”- Used for microwave applications where its performance surpassed that of other devices- Made possible by the use of the quantum mechanical effect called tunneling SCHEMATIC SYMBOL FOR TUNNEL DIODE PICTURE OF A TUNNEL DIODEk) Varactor Diode or Varicap Diode- Diode that has a variable capacitance which is a function of the voltage that is impressed on its terminal- Operated in reverse bias/ no current flow- Also known as Variceal diodes- Sort of semiconductor microwave solid-state device and it is used in where the variable capacitance is chosen which can be accomplished by controlling voltagel) Zener Diode- Used to provide a stable reference voltage- Works under reverse bias condition and found that when a particular voltage is reached it breaks down,- Commonly used as voltage regulator SCHEMATIC SYMBOL FOR ZENER DIODE ?RECTIFIER CIRCUITS  Rectifier is an electrical device that converts an alternating current (AC) into a direct one or direct current (DC) by allowing a current to flow through it in one direction only.a) Half Wave Rectifier- A simple type of rectifier made with single diode which is connected in series with load. SCHEMATIC DIAGRAM OF A HALF WAVE RECTIFIER WAVEFORM OF HALF WAVE RECTIFIERb) Full Wave Bridge Rectifier- A circuit which converts AC to DC using both half cycles of the applied AC voltage SCHEMATIC DIAGRAM FOR FULL WAVE BRIDGE RECTIFIER AND WAVEFORMSc) Center Tapped Full Wave Rectifier- Uses a center tapped transformer and two diodes to convert AC to DC signal SCHEMATIC DIAGRAM OF CENTER TAP FULL WAVE RECTIFIER CURRENT FLOW AND WAVE FORM? POWER SUPPLY     APPLICATION OF DIODES • Clipping Circuitso Usually used in FM transmitters where noise peaks are limited to a particular value so that excessive peaks are removed from them.• Clamping Circuitso Used to shift or alter either positive or negative peak of an input signal to a desired level• Logic Gates• Voltage Multiplier Circuitso Consist of two or more diode rectifier circuits which are cascaded to produce a DC output voltage equal to the multiplier of the applied input voltage.• Reverse Current Protectiono Helps avoid reverse polarity which damage some electronic devices• Voltage Spike Suppressiono In case of an inductor or inductive loads, sudden removal of supply source produces a higher voltage due to its stored magnetic field energy• Solar Panelso Used for protection of solar panels