Tunnel Diode Basics: Quantum Tunneling and Applications

The tunnel diode is a type of microwave semiconductor device widely used today. This page covers the fundamentals of tunnel diodes and their applications. The tunnel diode operates based on the principle of quantum tunneling, which is a majority carrier phenomenon.

Several conditions ensure a high probability of tunneling:

• Thin Depletion Zone: A narrow depletion region allows carriers to tunnel more easily.
• Heavy Doping: Heavily doped semiconductor material increases the concentration of carriers available for tunneling.
• Filled and Empty Energy States: There should be both filled energy states (where electrons can tunnel from) and empty energy states (where electrons can tunnel to) for each tunneling carrier.

Fig:1 Tunnel Diode Equivalent Circuit

From the tunnel diode equivalent circuit, it’s clear that a tunnel diode oscillates when the total reactance is zero and the negative resistance balances out the series resistance. There are two key frequency equations, outlined below:

Resistive Frequency, $F_r$ (Hz)

$F_r = \frac{1}{2 \pi R C_j} \sqrt{\frac{R}{R_s} - 1}$

Self-Resonant Frequency, $F_s$ (Hz)

$F_s = \frac{1}{2 \pi} \sqrt{\frac{1}{L_s C_j} - \frac{1}{(R C_j)^2}}$

Where:

• $R$ is the absolute value of the negative resistance (Ohms).
• $R_s$ is the series resistance (Ohms).
• $C_j$ is the junction capacitance (Farads).
• $L_s$ is the series inductance (Henrys).

Tunnel Diode Applications

Tunnel diodes find applications in various circuits, including:

• Amplifiers
• One-Shot Multivibrators
• Oscillators