ECCS-EPSRC: Towards ultralow-noise SiGe heterojunction bipolar transistors for quantum technology and beyond: epitaxial engineering of cryogenic charge transport

Quantum computing has inspired global excitement owing to its potential to efficiently solve computational problems that are extremely difficult on classical computers. However, significant technological advances are necessary to achieve the full potential of quantum computing. This project will investigate the origins of noise in SiGe-alloy-based transistors which could be used to measure the qubit state. Unlike current technology, these transistors have potential for future large-scale quantum computing platforms because they can be scaled and integrated into a complex circuit by leveraging mature Si technology. However, their noise performance remains inadequate for demanding applications in quantum computing. This project will address this knowledge gap via a collaborative research effort between researchers in the UK and US specializing in materials growth and device physics, respectively. The project will create fundamental knowledge regarding the structural and chemical properties, electrical characteristics, and microwave noise performance of SiGe heterojunction bipolar transistors (HBTs) optimized for cryogenic operation. The physical origin of discrepancies of cryogenic electrical transport characteristics from theory and their effect on microwave noise performance remain a topic of intense interest. This work will address this knowledge gap via a collaboration involving epitaxial growth of custom SiGe/Si epitaxial films and fabrication of HBTs, followed by materials and electrical characterization at cryogenic temperatures. The team combines expertise in the epitaxial growth of SiGe/Si heterostructures on Si and semiconductor materials and devices characterization (Myronov, UK) and in HBT device fabrication and characterization (Minnich, USA). The integration of growth, fabrication, and characterization tasks in a single effort will allow for significant new insights into HBT device physics which is not possible from independent investigations. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.