Physicists have found a way to access physical information that, according to a recent publication, has been hidden from science for 140 years.
As early as 1879, the physicist Edwin Hall discovered that electric currents bend when placed in a magnetic field, creating a voltage and a new electric field perpendicular to the current. Scientists have used this phenomenon, known as the Hall effect, to study the properties of materials such as semiconductors that make up chips – but frustrating the Hall effect preven ts scientists to perform certain measurements simultaneously. Researchers from IBM, the Korea Advanced Institute of Science and Technology, the Korea Research Institute of Chemical Technology and Duke University have now developed a one-shot technique to provide this information extract the carrier-resolved Photohall measurement technique. It could be particularly useful for the development of future solar cells and other materials.
"This could represent an exciting advance in the understanding of semiconductors," said Oki Gunawan, the study's first author and researcher at IBM's TJ Watson Research Center, Gizmodo said. "We hope it makes progress in the near future."
Electric charges move through semiconductors as discrete units called charge carriers: negatively charged electrons and positively charged "holes," electron voids in the material that can move in the same way as electrons. Scientists use the Hall effect to find out the properties of the charge carriers in a material, how fast they move, and how densely packed they are. More recently, they used the Hall effect to understand the effect of light on the materials they studied, since light striking certain materials creates electrons and holes. However, techniques based on the Hall effect can only measure the properties of the more abundant charge carrier, called the majority carrier, and not the properties of the minority and majority charge carriers at the same time . In principle, when more electrons are present, Hall effect measurements can only provide information about the electrons. If there are more holes, they can only reveal information about the holes.
Using a thought experiment, Gunawan was able to find a way to extract the information on minority cargo at the same time as the Majority Carrier Information . He envisioned two systems, each with the same majority charge carrier of the same density, traveling at the same speed but at different minority carrier speeds. Without additional energy, the two systems would behave the same way. However, if you add more energy from light pulses, they will behave slightly differently due to the effects of the minority carrier. From this thought experiment, he and his team developed an equation that simultaneously describes both the minority and majority carriers. This emerges from the publication of which was published last week in Nature.
However, the technique requires a way to reduce noise if the material is slow in perceiving the Hall effect or if there are other possible spurious signals. Previously, IBM researchers had developed a new type of system called a parallel dipole line. These are a pair of cylindrical magnets that together form a kind of magnetic field trap. They trapped two samples, one of silicon and one of a photosensitive material called perovskite, and extracted information about the charge carriers of the majority and the minority with their new equation.
However, measuring these properties is important to determine if a material is useful in a solar cell, Gunawan said. Moreover, it is a fundamental physical result that combines magnetic fields, electricity and light.
Of course there are limitations. Gunawan explained that the experimental approach can stall on materials with high carrier densities ̵
Nevertheless, this is exciting material. It is not often that you hear of a new fundamental physical result that changes our understanding of what is taught in basic physics courses.