---
title: "Esaki’s tunnel diode: more voltage could give less current"
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Materials · Measurements · Explanation

# Esaki’s tunnel diode: more voltage could give less current

Why did a heavily doped junction develop a falling section in its current curve?

Sandbox Physics · 2026-10-23

Nobel contribution: 1973-1

1. Make a narrow degenerate junction
2. Sweep forward bias
3. Record a current peak and valley
4. Compare occupied and empty states

The falling current reflects available states on both sides of the junction, together with barrier transmission.

## Heavy doping made tunneling accessible

Esaki’s germanium junction work in 1957, published in 1958, used very heavy doping. The narrow depletion region and degenerate carrier occupations allowed tunneling to compete strongly with ordinary diode conduction.

The measured current first rose and then fell as forward bias increased. This reproducible negative differential resistance was the observation that needed an explanation.

Sources: [1]

## Transmission alone does not set the current

An electron needs an occupied starting state and an available final state at the appropriate energy. Bias changes their overlap. Beyond the peak, fewer eligible states can contribute even though the voltage is larger.

Sources: [1]

## The valley has other contributions

At larger forward bias, ordinary diffusion current grows. Phonon-assisted and defect-related processes can fill the valley, so a measured peak-to-valley ratio depends on temperature and junction quality. The diode does not supply energy without a bias source.

Sources: [1]

## The barrier Lab explains one ingredient

A barrier-transmission calculation shows why a thin barrier can pass an electron. It has no degenerate semiconductor reservoirs, so it cannot on its own reproduce the tunnel diode’s full current curve. Esaki and Giaever share one 1973 award contribution but probed different electronic systems.

Sources: [1] [2] [3]

Continue with the physics

## Try the related models

### [Barrier transmission](https://sandboxphysics.com/labs/quantum-tunneling/)

Compare transmission as barrier width and incident energy change.

A single-particle barrier has no semiconductor occupations or superconducting density of states.

### [Transistor output curves](https://sandboxphysics.com/labs/transistor-output-characteristics/)

Change base injection and measure collector current.

The junction-transistor teaching model differs from the original point-contact device.

## Sources and reading notes

1. [Esaki: Long journey into tunneling (1973)](https://www.nobelprize.org/uploads/2018/06/esaki-lecture.pdf)

   Degenerate junctions, negative differential resistance and the spectroscopic information in tunneling.

2. [Giaever: Electron tunneling and superconductivity (1973)](https://www.nobelprize.org/uploads/2018/06/giaever-lecture.pdf)

   Metal–insulator–superconductor junctions probe an excitation gap, with temperature and junction quality important.

3. [Nobel Prize in Physics 1973: official award](https://www.nobelprize.org/prizes/physics/1973/summary/)

   Official attribution and award year. The observation or theoretical paper may be much earlier.

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