# Diode

What is a Diode?

The semiconductor is one of the fascinating concepts in the world of electronics compared to the passive components like the capacitors, resistors, and inductors. A diode is a type of semiconductor electronic device which is most widely used.

The semiconductor device, which acts as a one-way switch for current, is known as a diode. The device allows the easy flow of the current in one direction only; it puts a lot of restriction if the current tries to flow in the opposite direction.

The semiconductor diodes are also sometimes called rectifiers as the pulsating direct current (dc) is obtained by changing the alternating current (ac). The rating of the device is done based on its current and voltage capacity.

The polarity of the diode is determined by the anode (i.e., the positive lead) and the cathode (i.e., the negative lead). In most of the diodes, the current flow is allowed only when a positive voltage is applied to the anode. The configuration of a variety of diodes is displayed in the graphic below.

The current flow allowed by the diode is known as forward biased. When the diode does not permit the flow of the current, it is known as reverse biased, here the diode acts as an insulator.

Fun Fact: The arrow of the diode's symbol points against the direction of the electron flow, the reason being the symbol was conceived by the engineers, and their schematic diagram shows the current flowing from anode to cathode, i.e., from positive voltage to negative voltage source.

Diode Symbol

Below, the symbol of the diode is shown. The arrowhead indicates the direction of the conventional current, which is in the forward biased condition. The literal meaning is that the cathode is connected to the n side, and the anode is connected to the p side.

V - I Characteristics of a Diode

The below circuit diagram shows the arrangement for the PN junction diode. The voltmeter is connected in parallel, and an ammeter is a connector in series to the diode, whereas the variable resistor controls the supply. The diode diagram is shown below:

When the circuit is operational, if the diode is in forward biased condition, then at some point of a particular voltage, the potential barrier will get eliminated. Such voltage is known as the Cut-off voltage or Knee Voltage. The forward current will rise exponentially if the forward voltages go beyond the limit, the continuous rise in voltage of this will cause the device to get damaged due to overheating.

The following graph shows the state of diode conduction in forward and reversed biased conditions.

In reverse bias, the minority current carriers produce reverse current when there is an increase in the reverse voltage. Due to a further increase in reverse voltage, the reverse current also increases, which will cause a sudden breakdown at a certain point, causing permanent damage to the junction.

What is the non-ideal diode equation?

I = I₀($e^{\frac{qv}{kT}}$ - 1)

I0 is directly proportional to recombination, and thus, inversely proportional to material quality.

Ideal Diodes

The below-shown diode equation provides you with the expression for current flowing through the diode as a function of voltage. The Ideal Diode Law is shown as:

I = I₀($e^{\frac{qv}{kT}}$ - 1)

Where:

I = through the diode the net current flowing;

I0 = the diode leakage current density in the absence of light, known as the dark saturation current

V = voltage applied across the terminals of the diode;

q = absolute value of electron charge;

k = Boltzmann's constant; and

T = absolute temperature (K).

One of the critical parameters which differentiate the one diode from another is the dark saturation current (I0). I0 measures the recombination of the device. A diode will have a more considerable I0 value if the recombination of the diode is large.

1. Name the Types of Diode

Ans. The types of diode include:

Various types of diodes are available for using them in electronics design, namely a Backward diode, Barritt diode, Gunn Diode, light-emitting diodes, Photodiode, PIN diode, PN Junction, Laser diode, Step recovery diode, Schottky diodes, Tunnel diode, Varactor diode, and the Zener diode.

Backward Diode

It is also called a back diode, but it is not widely used. It is a PN junction diode that is similar to the tunnel diode process. Due to its specific properties, it can be utilized in a few specialized applications.

Baritt Diode

BARITT diode denotes the short term for Barrier Injection Transit Time diode, and it is mostly used in microwave application and is compared to widely used IMPATT diode.

Gunn Diode

This is also a PN junction diode that acts more like a semiconductor device, which has two terminals. Mostly it is used for generating the microwave signals.

Laser Diode

The laser diode cannot be mistaken to think as the commonly used LED (light-emitting diode) because it generates coherent light. In applications like CD drive, DVD, and laser light pointers for PPTs, the laser diodes are used.

Light Emitting Diode

The short form for the light-emitting diode is commonly known as LED and is the most utilized standard type of diode. The light is generated when a diode is connected in forward biased, and the current flows through the junctions.

Photodiode

The diode used to detect light is known as a photodiode. It has been discovered that when light strikes a PN junction, it creates electrons and holes. These diodes can produce even electricity.

PIN Diode

This type of diode has P-type and N-type standard regions, but the space between the two areas, which is the intrinsic semiconductor, does not have doping.

PN Junction Diode

The most standard and typical type of diode used today is the PN junction diode. These diodes come in small signal types for use in radio frequency or other low current applications, which are called as the signal diodes. There are other types called rectifier diodes, which are planned for high voltage and high current applications.

Zener Diode

The diode which provides stable reference voltage is known as the Zener diode; due to its stability, it is used in large amounts. Though it works under reverse bias conditions, it breaks down when a particular voltage is reached.

2. What are the Applications of Diode?

Ans.

Application of diode -

1. Rectifier

2. Over-voltage limiter

3. For clipping and clamping circuit

4. As a demodulator device

5. Freewheeling of the inductive energy

6. Variable capacitance diode- Used for tuning

7. Tunnel diode- Used for RF circuit

8. Zener diode- Used as a Voltage Regulator.

9. Light Emitting Diodes(LEDs)- For illumination purpose

10. Photo Diode- for the conversion of photon energy to electrical energy.