Semiconductors are the cornerstone of modern electronics. They’re used in solar cells, light emitting diodes (LEDs), microprocessors in laptops and cell phones, and more. Most of them are made of silicon, but silicon has its limitations. So for decades researchers have been exploring new materials with properties that make them good candidates for better, lighter, and cheaper energy-efficient lamps, solar cells, and even – someday, perhaps – solar energy-harnessing “paint.”
To decide whether a new material has promise as a semiconductor or meets a manufacturer’s specifications, companies need to be able to essentially count the number of freely moving “charge carriers” floating within the material, as well as their mobility or how easily they are able to move. Negative carriers are electrons; positive carriers are referred to as “holes” and are places where an electron is missing. Semiconductors are typically doped with impurities to increase the number of free electrons in one area of the material and the number of free holes in another area of the material, which gives the semiconductor a negative and positive side.
The traditional way of measuring charge carrier concentration, called the Hall method, takes some time and skill: it requires hand-soldering a series of metal electrical contacts onto a wafer of the material, exposing that wafer to a magnetic field, applying a current, and measuring a voltage. (See animation.)
New vs. Old: The traditional test for assessing the quality of a semiconductor, called the Hall method, measures the number of…