Scientists at RTI International are advancing the state of science in electronic devices for optical systems by using superlattice structures to optimize the performance of germanium optical detectors on silicon chips.

Their research, highlighted in the December issue of Nature Photonics, explains their use of thin films to overcome inefficiencies in crystal-structure mismatch between silicon and germanium. This structural mismatch results in an efficiency loss in electronics and is a major challenge in fabrication processes and widespread implementation. 

Solutions to date have mostly focused on engineering the buffer layers between silicon and germanium to accommodate this mismatch, but have yielded insufficient device performance levels. The RTI research team has incorporated a silicon-germanium superlattice structure appropriately to control the electric field in the active region of the optical detector and improve the device performance levels. 

The scientists’ goal is to demonstrate the integration of germanium photonic devices that use light to process information and then interact with silicon electronic circuits that use electrons to process information. Doing so will pave the way for next generation silicon-based optoelectronics for communication, computation and data transfer.

The scientists, Gary Bulman, Ph.D., and Jayesh Bharathan, of RTI’s Center for Solid State Energetics (CSSE), also published this research in the Journal of Electronic Materials. Bharathan is presently pursuing a doctoral degree in materials science and engineering at NC State.  

“This research shows that high-performance germanium photo-detectors can be fabricated on commonly available silicon wafers, using superlattice structures to carefully optimize the devices," said Rama Venkatasubramanian, Ph.D., director of RTI’s CSSE. “This device technology will become important for next-generation communication and computational devices and also appears attractive from a commercial manufacturing standpoint.”