Tunnel Diode vs. P-N Junction Diode: Key Differences

This article compares the tunnel diode and the p-n junction diode, highlighting the key differences between them. Both are semiconductor diodes used as low-power devices, but they operate on different principles and have distinct applications.

Tunnel Diode

Here’s a breakdown of the tunnel diode’s characteristics:

• Low Noise: Generally produces less noise during operation.
• Preferred Semiconductors: Germanium (Ge) and Gallium Arsenide (GaAs) are commonly used.
• Tunnelling Current: Current primarily consists of majority carriers, flowing from the n-side to the p-side.
• High Doping Levels: The p and n sides are heavily doped.
• Reverse Voltage Behavior: A large current flows at a small reverse voltage due to the significant overlap between the conduction and valence bands. This makes it useful as a frequency converter.
• Negative Resistance: Exhibits negative resistance characteristics, making it suitable for reflection amplifiers and oscillators.
• Fast Response: Majority carrier current responds very quickly to voltage changes, ideal for microwave applications.

P-N Junction Diode

Now let’s look at the features of a typical p-n junction diode:

• Moderate Noise: Produces a somewhat higher noise level compared to tunnel diodes.
• Preferred Semiconductors: Silicon (Si) and Germanium (Ge) are often employed.
• Current Flow: Current primarily consists of minority carriers, flowing from the p-side to the n-side.
• Normal Doping: Doping levels are standard on both the p and n sides.
• Reverse Voltage Behavior: Leakage current is extremely small up to a certain reverse bias voltage, then increases sharply at the breakdown voltage.
• No Negative Resistance: Does not exhibit negative resistance, which means it’s typically used as a detector and in RF mixers.
• Slower Response: Majority carrier current doesn’t respond as quickly to voltage changes, making it more suitable for low-frequency applications.