- Rhombohedral epitaxy of single crystal SiGe on sapphire substrates
- Modeling of SiGe on sapphire
- Ph.D. (2013), Dept. of Materials Science and Engineering, University of Michigan, Ann Arbor, MI
- B.Sc. (2008), Dept. of Materials Science and Engineering, Iowa State University, Ames, IA
- SiGe Rhombohedral Epitaxy: Silicon (Si) is the foundation for all modern integrated circuit technology, but is approaching the limits of possible device speed. Germanium (Ge) is a higher mobility semiconductor than Si, but is more expensive and lacks the oxide layer Si forms necessary to device fabrication. SiGe is an alloy of these two elements, leveraging the best properties of both. As semiconductor devices only use the top ~100 nanometers of the wafer, and as such, a thin layer of SiGe on an inexpensive substrate suffices. However, this remained elusive, despite decades of research, until recently discovered in our lab. Sapphire (Al2O3) forms a rhombohedral crystal structure of aluminum (Al) and oxygen (O) atoms. In contrast, Si, Ge, and SiGe all form a cubic crystal structure. Traditionally, dissimilar crystal structures are considered incompatible, but these two materials are an exception. When oriented a certain way, the (111) SiGe crystal plane can match to the (0001) Al2O3 crystal plane. SiGe films over 99% composed of one crystal have been produced in our laboratory, but required very high (1100°C) temperatures to deposit a Si interfacial layer between Al2O3 and the usable SiGe film. Current work focuses on streamlining the process to eliminate the Si layer and the need for high temperatures, while still producing high quality SiGe films repeatedly. This research represents a new field in semiconductor manufacturing to combine previously incompatible materials, opening the possibility that other cubic semiconductors are compatible with Al2O3. Many new devices and improved material combinations would follow, with large economic and technological implications.
- SiGe Modeling: Supporting the above experimental research is a concurrent simulation effort aimed at modeling how SiGe and Al2O3 bond at the atomic level. Thermal expansion calculation of how each material changes under experimental conditions has led to halving the deposition temperature and eliminating the Si interfacial layer and a likely model for how bonding occurs at the interface. Such a model is useful in predicting any other future combinations of cubic materials with Al2O3.
- Duzik, A., Y. Park, and S.H. Choi, Towards Rhombohedral SiGe Epitaxy on 150mm c-plane Sapphire Surfaces, Proc. SPIE. 9434, Nanosensors, Biosensors, and Info-Tech Sensors and Systems 2015, doi: 10.1117/12.2085310, Mar. 2015