Diode: points that you should never forget about this important semiconductor

Electrical and electronic circuits can't even imagine without resistors. But there is one more component in this stream which is the most active component too. 'Signal Diode' is the one which doesn't indulge in linear behaviour in respect to the applied voltage. It has an exponential I-V relationship. Diodes are, otherwise, unidirectional semiconductor devices, which allow current to flow in one direction only.

Diodes are made from a single piece of semiconductor material which has a positive “P-Region”. The other end is negative “N-region” which holds resistivity value between a conductor and an insulator.

1. Definition of Diode: 

It is a two-terminal unilateral semiconductor device and the two terminals are known as anode and cathode. We compare a diode's basic features with that of a switch which doesn't conduct current in either directions, if opened, and when closed it conducts current in both directions. Diodes are made from semi-conductor materials like silicon and germanium.

2. Voltage Characteristic: 

If the diode is forward biased, then voltage and current can get recorded. The diode can also be turned into a reverse biased one. While a forward biased diode starts conducting current at the junction voltage, if we reverse the voltage, then a small amount of current gets leaked.

At a certain voltage limit, like 10V to 2000V, the barrier layer's insulation breaks down, all of a sudden, and the current is increased suddenly too. Some diodes also result in burn-out in such cases.

3. Zener Diode: 

This kind of diode is designed for reverse biased configuration. It behaves like a normal diode only but if the breakdown-voltage is -5.6V, then the current rises rapidly. The output voltage stays at a constant level of 5.6V and it's known as voltage clamp. When voltage crosses 5.6V, a current flows through the diode and the voltage is kept constant, and this function is called voltage regulators.

4. Light Emitting Diode: 

The light emitting diode or LED has its forward voltage at about 2.2 V. Its voltage current characteristic acts just like an ordinary diode and the LED version can also bear a small reverse voltage, though 20V reverse voltage can damage a LED.

5. How Diodes work? 

A diode starts operating when a voltage signal is applied to its terminals. If DC voltage is applied then the circuit is called “Biasing”. If Forward Biasing takes place, it means the diode is ON. It signifies that the anode has received positive or higher potential while the cathode has received negative or lower potential. The OFF state is received through reverse Biasing which means exactly the opposite from the ON stage.

During its ON stage the practical diode offers Forward Resistance which requires a forward bias voltage to switch the ON condition. If no voltage is applied then the diode remains at its OFF state.

6. Material Basics in Diodes: 

Resistivity is a key factor in diodes as all other electrical or electronic component or device. Based on resistivity, materials for diodes can be classified into three categories : conductors, insulators and semiconductors.

Conductors mean low values of resistivity which allow passing electrical current easily. Good conductors include Copper, Aluminium, Silver and Carbon-like non-metals. Most metals are good conductors of electricity, but their resistivity factor increases with surrounding temperatures. Insulators are exact opposites of conductors as no current flows through these non-metallic components. They have very high resistance power and in electrical and electronic circuits, insulators play significant role. Semiconductor materials have medium electrical properties. As the amount of added impurities to a semiconductor material can be control, it also allows in controlling conductivity. The most used material in this case is silicon as they act as very good insulators as well as resistors in diodes. 

Source: Book Electronic by Boylestad