In this note, we are going to learn about a topic called “What is Tunnel Diode?” and its characteristics. Also about its construction, working, VI characteristics, applications as well. Welcome to Poly Notes Hub, a leading destination for Engineering Note.
Author Name: Arun Paul.
What is Tunnel Diode?
A tunnel diode is a form of semiconductor diode that can operate at extremely high frequencies, well into the microwave range, thanks to quantum mechanical processes.
The tunnel diodes include a strongly doped PN junction. The PN junction is typically around 10nm broad. Heavy doping causes a broken bandgap, in which conduction band electron states on the N side are roughly aligned with valence band hole states on the P side.
Tunnel Diode Symbol
Tunnel diodes are often composed of germanium, but they can also be manufactured of gallium arsenide or silicon. They can function as oscillators, amplifiers, frequency converters, and detectors.
It has been shown that increasing the concentration of impurity atoms in a normal PN junction (by 1000 times or more) entirely alters its properties. This creates a new form of diode known as the tunnel diode. Dr. Leo Esaki created it in 1958. That is why a tunnel diode is also called an “Esaki diode”.
Tunnel Diode Diagram
Below we describe the construction of tunnel diode –
A tunnel diode is made of semiconductor materials, commonly germanium or gallium arsenide. It is made up of a severely doped P-type semiconductor region and a heavily doped N-type semiconductor region, which together constitute the P-N junction. The doping levels are chosen to result in a thin depletion area near the junction.
Semiconductor materials are typically formed into tiny, cylindrical or disc-shaped structures. Electrical connections are made by attaching metal contacts to each doped region. These connections enable the application of a voltage across the P-N junction.
Doping levels on both sides of the junction are crucial for tunnel diode design. Heavy doping provides a steep potential energy barrier at the junction, which facilitates electron tunneling.
Tunnel Diode Working Principle
A tunnel diode, also called an Esaki diode, works on the basis of quantum mechanical tunneling. It is made of a strongly doped semiconductor material that forms a P-N junction with a very tiny depletion area. When a forward bias voltage is supplied, electrons in the N-type material gather sufficient energy to quantum mechanically tunnel through the narrow depletion area. This mechanism causes a rapid increase in current, resulting in an area of negative differential resistance. In this zone, a rise in voltage causes a drop in current. Tunnel diodes are most efficient in the negative resistance area, making them ideal for applications that require high switching speeds, such as microwave oscillators and amplifiers.
However, their limited operational range and sensitivity to temperature swings prevent broad adoption. Despite these restrictions, tunnel diodes are nevertheless useful in niche applications where their unique features are favorable.
Tunnel Diode VI Characteristics
Fig shows the V-I characteristics of a tunnel diode and describe the tunnel diode characteristics –
From the characteristics curve, we see that as the applied forward voltage is increased from zero, the current increases rapidly until it reaches its maximum value known as peak current as indicated by the point. The corresponding value of the forward voltage is indicated by the peak voltage. This voltage is typically 65mV for germanium and 160mV for gallium arsenide tunnel diode.
Tunnel Diode Application
Below we listed some important applications of tunnel diodes –
- Used as a ulta high speed switching device.
- As a logic memory storage device.
- As a microwave oscillator at frequencies of 10 GHz.
- Also used in relaxation oscillator.
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