Skip to Content

No P-N Intended

A cracked crystal launched the silicon revolution.
February 1, 2003

When Russell Ohl began working at Bell Laboratories in 1927, vacuum tubes were seen as the future of electronics. It was his chance discovery, however, that led to the creation of both the transistor and the solar cell and helped spark the “silicon revolution.”

In the late 1930s Ohl was a radio researcher trying to create a receiver that would be more effective than vacuum tubes. The tubes easily picked up low-frequency radio signals, but had trouble with higher frequencies such as those being tested in radar-a technology that was gaining importance as war brewed overseas. Ohl thought an alternative might lie in the crystal receiver, an antiquated radio device from the 1920s. He devoted himself completely to his research: when his workweek was shortened during the Depression, Ohl used his extra time to study crystal structure.

Crystal receivers were tricky, poorly understood devices. To get a signal, an operator would search the surface of a crystal with a metal strand for the “hot spot,” which caused current flow in only one direction. After exhaustive experimentation, Ohl concluded that the best receivers were the elements now known as semiconductors. He theorized that purer materials would make better receivers and had special samples prepared for his tests.

Early in 1940 Ohl examined a silicon sample that had a crack down its middle. Something was strange about that crystal: when it was exposed to light, the current flowing between the two sides of the crack jumped significantly. Baffled, Ohl showed the bizarre sample to his Bell colleagues, who were equally amazed. No one had ever seen a photovoltaic reaction like it.

The researchers discovered that the crack was a dividing line between two  impurities in the silicon. One type of silicon had an excess of electrons, the other a deficit. They named them p-type for positive and n-type for negative, and the barrier between the two was dubbed the p-n junction. Gradually, the group realized that photons give the excess electrons in the n-type material enough of an energy boost to cross the junction and produce a current.

Although Ohl’s original crystals didn’t produce nearly enough power for commercial use, his research into p- and n-type silicon led to Bell Labs’ creation of the first modern solar cell in 1954. The first transistors also were based on the p-n junction. When Ohl held his unusual crystal to the light in 1940, he unwittingly began the transition from vacuum tubes to integrated circuits.

Keep Reading

Most Popular

still from Embodied Intelligence video
still from Embodied Intelligence video

These weird virtual creatures evolve their bodies to solve problems

They show how intelligence and body plans are closely linked—and could unlock AI for robots.

pig kidney transplant surgery
pig kidney transplant surgery

Surgeons have successfully tested a pig’s kidney in a human patient

The test, in a brain-dead patient, was very short but represents a milestone in the long quest to use animal organs in human transplants.

conceptual illustration showing various women's faces being scanned
conceptual illustration showing various women's faces being scanned

A horrifying new AI app swaps women into porn videos with a click

Deepfake researchers have long feared the day this would arrive.

thermal image of young woman wearing mask
thermal image of young woman wearing mask

The covid tech that is intimately tied to China’s surveillance state

Heat-sensing cameras and face recognition systems may help fight covid-19—but they also make us complicit in the high-tech oppression of Uyghurs.

Stay connected

Illustration by Rose WongIllustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at customer-service@technologyreview.com with a list of newsletters you’d like to receive.