Scientists at Stanford University have discovered a new way to use some of the oldest known semiconductor materials to improve infrared technology.
Their work could lead to smaller, cheaper, and more efficient infrared devices used in environmental monitoring, medical testing, and industrial sensors.
Semiconductors are materials that control how electricity flows and are essential for modern electronics such as microchips, LEDs, and sensors.
The Stanford researchers focused on a group of semiconductors known as IV–VI materials, specifically lead selenide and lead tin selenide.
These materials were first studied more than a century ago, making them some of the earliest semiconductors ever discovered.
Although scientists have known about these materials for a long time, they have rarely been used in modern electronics.
Now, researchers say they have found a way to combine them with newer semiconductor technologies to create improved infrared light-emitting devices.
The team developed a new type of infrared diode that emits light at longer wavelengths, between about 4,000 and 5,000 nanometers. This range is particularly useful for detecting gases in the air, including greenhouse gases, and for medical monitoring devices such as carbon dioxide sensors.
One surprising advantage of the new design is that the materials are highly tolerant of defects. In most semiconductor devices, tiny flaws in the crystal structure can ruin performance. Manufacturing semiconductors with perfect precision is extremely difficult, especially at the nanoscale.
However, the materials used in this study still performed well even when they contained large numbers of defects. This property could make the technology easier and cheaper to manufacture. Because these semiconductors have been studied for decades, they may also be produced using existing chip-making equipment instead of requiring entirely new factories.
The research took about five years to complete. A major challenge was figuring out how to combine the old materials with modern semiconductors so that their crystal structures could connect properly. In semiconductor devices, layers of different materials must bond together perfectly at the atomic level without adhesives.
To achieve this, the researchers used a method called molecular beam epitaxy. This technique builds crystals one atomic layer at a time, allowing scientists to carefully control how the materials form.
The first study, published in Advanced Optical Materials, demonstrated how these older semiconductors could be integrated with a widely used semiconductor called gallium arsenide. The resulting devices produced surprisingly bright infrared light even though the crystals contained many structural defects.
A second study, published in Nano Letters, explored how the crystal structure of the material could be carefully adjusted. By making small changes in temperature, the researchers were able to shift the crystal between two different ordered structures. This shift affects how infrared light travels through the material.
By controlling the crystal structure, scientists can adjust how much light passes through the device, turning it on or off or changing its intensity. They can also alter other properties of the light, such as its phase and polarization.
Infrared technology has often received less attention than visible-light LEDs, partly because infrared light cannot be seen by the human eye. As a result, many infrared devices today are bulky and expensive.
The Stanford team believes their new approach could help create a new generation of compact, affordable infrared devices that are easier to manufacture and more widely used in environmental monitoring, medicine, and industry.
Source: Stanford University.
