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What is a Tunnel Diode?
What is a Tunnel Diode? A tunnel diode (also known as an Esaki diode) is a type of semiconductor diode that has effectively “negative resistance” due to the quantum mechanical effect called tunneling. Tunnel diodes have a heavily doped PN junction that is about 10 nm wide. The heavy doping results iRead more
What is a Tunnel Diode?
A tunnel diode (also known as an Esaki diode) is a type of semiconductor diode that has effectively “negative resistance” due to the quantum mechanical effect called tunneling. Tunnel diodes have a heavily doped PN junction that is about 10 nm wide. The heavy doping results in a broken bandgap, where conduction band electron states on the N-side are more or less aligned with valence band hole states on the P-side.
The application of transistors in a very high-frequency range is hampered due to the transit time and other effects. Many devices use the negative conductance property of semiconductors for these high-frequency applications. A tunnel diode is one of the most commonly used negative conductance devices. It is also known as Esaki diode after L. Esaki for his work on this effect.
The concentration of dopants in both p and n regions is very high, at around 1024 – 1025 m-3. The PN junction is also abrupt. For these reasons, the depletion layer width is very small. In the current-voltage characteristics of the tunnel diode, we can find a negative slope region when a forward bias is applied.
The name “tunnel diode” is due to the quantum mechanical tunneling being responsible for the phenomenon that occurs within the diode. The doping is very high so at absolute zero temperature, the Fermi levels lie within the bias of the semiconductors.
Characteristics of Tunnel Diode
When a reverse bias is applied the Fermi level of the p-side becomes higher than the Fermi level of the n-side. Hence, the tunneling of electrons from the balance band of the p-side to the conduction band of the n-side takes place. With the interments of the reverse bias, the tunnel current also increases.
When a forward bias is applied the Fermi level of the n-side becomes higher than the Fermi level of the p-side, thus the tunneling of electrons from the n-side top-side takes place. The amount of the tunnel current is very large than the normal junction current. When the forward bias is increased, the tunnel current is increased up to a certain limit.
When the band edge of the n-side is the same as the Fermi level on the p-side, the tunnel current is maximum with the further increment in the forward bias the tunnel current decreases and we get the desired negative conduction region.
Tunnel Diode Applications
A tunnel diode is a type of sc diode which is capable of very fast and in microwave frequency range. It was the quantum mechanical effect which is known as tunneling. It is ideal for fast oscillators and receivers for its negative slope characteristics. But it cannot be used in large integrated circuits – that’s why its applications are limited.
When the voltage is first applied current stars flow through it. The current increases with the increase of voltage. Once the voltage rises high enough suddenly the current again starts increasing and tunnel diode stars behave like a normal diode. Because of this unusual behavior, it can be used in several special applications started below.
Oscillator Circuits:
Tunnel diodes can be used as high-frequency oscillators as the transition between the high electrical conductivity is very rapid. They can be used to create oscillation as high as 5Gz. Even they are capable of creativity oscillation up to 100 GHz in appropriate digital circuits.
Used in Microwave Circuits:
Normal diode transistors do not perform well in microwave operation. So, for microwave generators and amplifiers tunnel diodes are used. In microwave waves and satellite communication equipment, they were used widely, but lately, their usage is decreasing rapidly, as transistors that operate in this frequency range are becoming available.
Resistant to Nuclear Radiation:
See lessTunnel diodes are resistant to the effects of magnetic fields, high temperature, and radioactivity. That’s why these can be used in modern military equipment. These are used in nuclear magnetic resource machines also. But the most important field of its use is satellite communication equipment.
What is the atmosphere made up of?
The word 'atmosphere' means a gaseous cover enveloping a planet. Without the atmosphere life would not have been possible on the Earth: One-fifth of the atmosphere is oxygen and four-fifths is nitrogen. Like the Earth's interior, the atmosphere too is made up of several layers. All animals and plantRead more
The word ‘atmosphere’ means a gaseous cover enveloping a planet. Without the atmosphere life would not have been possible on the Earth: One-fifth of the atmosphere is oxygen and four-fifths is nitrogen. Like the Earth’s interior, the atmosphere too is made up of several layers. All animals and plants live in the lowermost layer of the atmosphere called the ‘troposphere. All-weather phenomena take place in the troposphere. Even airplanes fly on the outer edge of the troposphere. The stratosphere, the mesosphere, the ionosphere, and the exosphere lie above the troposphere.
See lessWhy do we not fall off from the Earth?
Gravity is the force of the Earth that attracts every object towards itself. From our perspective, this force always acts downwards. For a long time, people did not believe that the Earth is round because then the people 'underneath the sphere would have actually fallen. In 1687, a physicist, IsaacRead more
Gravity is the force of the Earth that attracts every object towards itself. From our perspective, this force always acts downwards. For a long time, people did not believe that the Earth is round because then the people ‘underneath the sphere would have actually fallen. In 1687, a physicist, Isaac Newton, proved that the force of gravity always acts towards the center of the Earth. On the Earth, the force of gravitation always acts ‘downwards irrespective of Eskimos in the Arctic region, people in Europe, or inhabitants of Australia.
See lessHow did we discover that the Earth is round?
About 3000 years ago people believed that the Earth was flat. But people wondered why ships disappeared at the horizon Sailors too returned from journeys and were proof that ships did not fall off the edge of the Earth. The simplest explanation was: that the Earth must be round. The final proof cameRead more
About 3000 years ago people believed that the Earth was flat. But people wondered why ships disappeared at the horizon Sailors too returned from journeys and were proof that ships did not fall off the edge of the Earth. The simplest explanation was: that the Earth must be round. The final proof came in the year 1522 after the expedition of Ferdinand Magellan, who was the first to sail around the Earth.
See lessHow do we discover what is inside the Earth?
Caves and mines go only up to 1-2 km inside the Earth. Even the deepest wells of the world, such as the one 12 km deep in the Russian Kola Peninsula or the 9-km-deep one in the Upper Palatinate, hardly scratch the Earth's crust. One can 'look' deep inside the Earth in the aftermath of earthquakes orRead more
Caves and mines go only up to 1-2 km inside the Earth. Even the deepest wells of the world, such as the one 12 km deep in the Russian Kola Peninsula or the 9-km-deep one in the Upper Palatinate, hardly scratch the Earth’s crust. One can ‘look’ deep inside the Earth in the aftermath of earthquakes or by creating nuclear explosions. The explosions generate sound or seismic waves. They also throw off rock particles. By measuring their intensity and timings, scientists discover the composition of the Earth’s interiors.
See lessWhat is the internal structure of the Earth?
Like an onion, the Earth has several layers. The outermost layer, the Earth's crust, has an average depth of about 40 km. As compared with the diameter of the Earth, which is around 12,700 km, the Earth's crust is very small. It is primarily made up of solid rocks. Below the crust is the mantle, reaRead more
Like an onion, the Earth has several layers. The outermost layer, the Earth’s crust, has an average depth of about 40 km. As compared with the diameter of the Earth, which is around 12,700 km, the Earth’s crust is very small. It is primarily made up of solid rocks. Below the crust is the mantle, reaching a depth of about 2900 km. Due to the heat inside the Earth, the mantle consists of solid and molten rocks. Below the mantle is the core, made up of iron and nickel. The deeper one travels inside the Earth, the hotter it is. The temperature in the core is between 4000 and 5000°C
See lessWhat is the external structure of the Earth?
It has been known for more than 2000 years that the Earth is round, but we were able to actually see this much later only when we flew into space. The knowledge of why we do not fall off the Earth is much more recent. A journey as described by author Jules Verne in his book Journey to the Center ofRead more
It has been known for more than 2000 years that the Earth is round, but we were able to actually see this much later only when we flew into space. The knowledge of why we do not fall off the Earth is much more recent. A journey as described by author Jules Verne in his book Journey to the Center of the Earth was, after all, impossible. Only one thing was known: the Earth is made up of soil, rocks, and water. Today, we know that the Earth is also surrounded by an air cover called the atmosphere.
See lessCharging supercapacitors with reversed polarity
Electrolytic capacitor polarization is initially set at the factory by applying voltage to form the insulating oxide layer. That is why caps have a polarity and these standard supercaps are no different. Reversing the polarity will damage the original insulating layer first and then start to form aRead more
Electrolytic capacitor polarization is initially set at the factory by applying voltage to form the insulating oxide layer.
That is why caps have a polarity and these standard supercaps are no different. Reversing the polarity will damage the original insulating layer first and then start to form a new insulating layer with the applied polarity. It is not something that should be allowed to happen, so consider the capacitors damaged, or at least degraded, and they could be unstable and dangerous too.
Here is also what manufacturer says about reversing the polarity:
https://maxwell.com/wp-content/uploads/2021/08/Notes_on_Using_Ultracapacitor_Cells.pdf
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