Cum laude for light-emitting silicon
Light-emitting chips would revolutionize microelectronics. Elham Fadaly laid the basis for this ‘holy grail’. She managed to let silicon emit light, by forcing it into a new shape. Based on this groundbreaking work, Fadaly obtained her PhD cum laude at the department of Applied Physics.
Adapted from an original text by Hilde van Genugten - de Laat, Science Information Officer at TU/e
Silicon is a powerful material pervading our everyday lives. Silicon-based microchips are the basis of nearly every electronic device used in our houses, cars, smart gadgets, and even in the human body. But silicon is an extremely inefficient light emitter, hindering it from being employed in laser devices, the basis of high-speed communications. Solving this holy grail would revolutionize computing, allowing chips to communicate faster than ever before.
Silicon germanium (SiGe) alloys exist naturally in an optically inactive cubic structure. Efficient light emission has been predicted to be possible when forcing the silicon into a hexagonal structure. It is, however, extremely challenging to achieve the hexagonal structure in this class of materials.
From cubic to hexagonal
During her Ph.D., Fadaly, together with other colleagues, developed high-quality hexagonal Si-based alloys. These alloys proved to be capable of emitting light efficiently and had excellent optoelectronic properties. Fadaly: ‘I changed the arrangement of the atoms of the natural cubic silicon structure to the promising hexagonal one. To do so, I used hexagonal nanowire templates to transfer the crystal structure to SiGe in a core-shell geometry by utilizing the crystal transfer technique.’
In collaboration with her colleagues, Fadaly has proved the quality of the fabricated material via several structural and optical characterization techniques. She identified an unconventional type of crystal defect in this novel material and understood its formation mechanism, which helped to avoid its occurrence and produce high-quality crystals. But that is not all. She also made it possible to tune the emitted wavelength over a broad range while preserving superior optical properties by controlling the SiGe alloy composition. Her work was proclaimed Breakthrough of the Year by Physics World and she received the Nanotechnology Young Researcher runner-up award.
Having proved efficient light emission in silicon, demonstrating lasing in this novel material is the next important milestone. The finding of this work could potentially lead to the development of the first silicon-based laser or mid-infrared light detectors, both of which would be compatible with the current silicon technology. These lasers could be deployed in several applications such as telecommunications, LIDAR for self-driving cars, and chemical sensors for medical diagnosis or measuring air and food quality.
TU/e is coordinating a new Horizon 2020 project, Opto Silicon, whose vision is to integrate light-emitting devices, based on hexagonal silicon-germanium with existing Si electronics and passive Si-photonics circuitry.