In a significant stride towards advancing microelectronics technology, researchers have successfully demonstrated the formation of polycrystalline germanium-tin (GeSn) films with high tin (Sn) content, potentially revolutionizing the energy sector. The study, led by Dr. V O Yukhymchuk from the V. Lashkaryov Institute of Semiconductor Physics at the National Academy of Science of Ukraine, explores the use of laser-induced crystallization to enhance the incorporation of Sn atoms into germanium (Ge) lattices, a critical factor for developing efficient, silicon-compatible optoelectronic devices.
The challenge of incorporating high Sn content into Ge has long been a hurdle due to Sn’s low solubility in Ge. However, Yukhymchuk and his team have found a clever workaround by doping the films with carbon (C) atoms. “Carbon atoms reduce local stresses, which in turn increases the ability of Sn atoms to be incorporated into the Ge crystal lattice,” explains Yukhymchuk. This innovation allows for the creation of polycrystalline GeSn films with approximately 8.0 atomic percent Sn, a substantial improvement over the natural solubility limit of 0.5%.
The researchers employed both femtosecond and continuous wave laser annealing techniques, alongside traditional thermal annealing, to crystallize the GeSn and GeSn:C films deposited on silicon (Si) substrates via thermal evaporation. The study found that pulsed laser treatment was the most effective method for Sn incorporation into the Ge lattice. Moreover, the addition of carbon significantly enhanced the thermal stability of the films.
The implications of this research are profound for the energy sector. GeSn alloys with direct bandgaps in the near-infrared and mid-infrared ranges hold promise for developing advanced photonic devices, such as lasers and detectors, that are compatible with existing silicon complementary metal-oxide-semiconductor (CMOS) processes. “The advantages of polycrystalline GeSn compared to its epitaxial counterpart are significantly lower costs and the possibility to grow these films on a variety of substrates,” notes Yukhymchuk.
The study, published in the Institute of Physics Publishing journal Materials Research Express (which translates to “Materials Research Express” in English), utilized a suite of analytical techniques, including Raman spectroscopy, atomic force microscopy (AFM), X-ray diffraction (XRD), and scanning electron microscopy (SEM), to characterize the films. The results revealed that, under identical laser processing conditions, the proportion of Sn atoms incorporated into the Ge lattices in both GeSn and GeSn:C films was approximately the same. However, the films doped with carbon exhibited superior thermal stability.
This breakthrough could pave the way for more efficient and cost-effective optoelectronic devices, potentially transforming the energy sector by enabling advanced silicon-based technologies. As the world continues to seek innovative solutions for sustainable energy, the development of high-performance, low-cost materials like polycrystalline GeSn films becomes increasingly vital. Yukhymchuk’s research offers a promising path forward, demonstrating the power of interdisciplinary collaboration and cutting-edge technology in driving progress.