Tunnel Diode: Advantages and Disadvantages

This page explores the advantages and disadvantages of tunnel diodes, outlining their benefits and drawbacks.

What is a Tunnel Diode?

Introduction:

Tunnel diodes are heavily doped p-n junction diodes exhibiting negative resistance over a portion of their characteristic curve (see Figure 1). They are also known as Esaki diodes.

These diodes are characterized by heavy doping and very thin depletion zones, specifically designed to encourage quantum mechanical tunneling currents to form.

Tunnel diodes find applications as amplifiers, oscillators, and one-shot multivibrators.

Figure 1: Tunnel diode characteristic

Compared to normal p-n junction diodes, tunnel diodes possess these distinct features:

• High Doping Levels: Doping levels on both the p-side and n-side are exceptionally high.
• Thin Depletion Zones: They feature very thin depletion zones, ranging from approximately 3 to 100 angstroms.
• Majority Carrier Tunneling: Tunneling current is primarily composed of majority carriers, specifically electrons moving from the n-side to the p-side.
• Preferred Semiconductors: Germanium (Ge) and Gallium Arsenide (GaAs) are commonly used in tunnel diode fabrication.

Benefits or Advantages of Tunnel Diodes

The following are the benefits or advantages of Tunnel diodes:

• High-Speed Response: The current, carried by majority carriers, in a tunnel diode responds much faster to voltage changes. This makes them useful for high-speed microwave applications.
• Low Power Consumption: They are low-power devices, efficient in their energy usage.
• Frequency Conversion: Large current flow at small reverse voltage values, due to the overlap between the conduction and valence bands, makes them suitable for frequency conversion.
• Negative Resistance: The negative resistance characteristic, as illustrated in Figure 1, is useful for reflection amplifiers and oscillators.
• Low Noise: Tunnel diodes are known for their low-noise operation.
• Simplicity and Low Cost: They are relatively simple devices to manufacture and therefore are low cost.
• Low Power Consumption: As mentioned previously, they require very little power to operate.

Drawbacks or Disadvantages of Tunnel Diodes

The following are the disadvantages of tunnel diodes:

• Low Output Voltage Swing: They deliver a low output voltage swing compared to other types of diodes.
• Limited Power Output: Power output levels are restricted to only a few milliwatts. This is because the applied DC potential must be less than the bandgap potential of the diode.