SiGe  technology

higher operation frequencies can be fabricated as shown in Table 2.

Ultra-CMOS

Rhombohedral semiconductors on trigonal substrates can improve the following products: Ultra fast Complementary Metal Oxide Semiconductor (CMOS) chipsets; Hetero- junction Bipolar Transistors (HBT); Thermo-Electric (TE) device; photo-voltaic solar cell device; advanced detectors; high frequency high power transmitters; and others as shown in Figure 3.

Before our research, trigonal crystal materials were not considered to be compatible with cubic semiconductors. The hybrid structure of rhombohedrally deformed cubic semiconductors and trigonal crystals create new opportunities to fabricate completely new single-crystal alloy structures for ultrafast semiconductor chip development beyond the silicon-based chip technology.

Since the NASA’s rhombohedral SiGe can allow faster electron motion with higher germanium contents than single crystal silicon has, it will offer the development of ultrafast chipsets for numerous applications. In addition, hexagonal space symmetry materials can be grown on trigonal space symmetry materials such as GaN on c- plane sapphire.

We summarize the following inter-crystal-structure epitaxial relation between cubic [111] direction, trigonal [0001] direction, and hexagonal [0001] direction for further possibilities as shown in Figure 4. This diagram shows the possibility of epitaxial growth from underlying substrate material of one space symmetry group to an epitaxial layer of a different space symmetry group. A solid line means that it is possible to form a single crystal layer, and a dashed line means that double position defect creates huge difficulties to form a single crystal. A round green circle indicates that twin detection XRD methods can be applied and an empty circle means that twin detection XRD methods do not work.

Table 1. Comparison of Si, SOI, SiGe on Si, and LM-SGOI technologies

Table 2. Expected operation speed of a transistor with various mobilities and gate lengths

This research has won a R&D100 award in 2009 and it has double-edge impact as the world’s first development of single crystalline rhombohedral SiGe semiconductors on trigonal substrates and opening the first window to hybrid crystal structure alloy engineering, namely, “Rhombohedral Hybrid Band-gap Engineering” with innovative XRD methods.

Further reading

Yeonjoon Park, Sang H. Choi, Glen C. King, and James R. Elliott “Hybrid Bandgap Engineering for Rhombohedral Super-Hetero-Epitaxy”, NASA Case No. LAR 17405-1, June 28, 2006. [patent filed on April 23, 2007] Yeonjoon Park, Sang H. Choi, Glen C. King, and James R. Elliott, “Supporting DATA (XRD and EBSD) for Hybrid Bandgap Engineering for Rhombohedral Super-Hetero-Epitaxy”, NASA Case No. LAR 17519-1, March 12, 2007. [patent filed on August 25, 2008] Yeonjoon Park, Sang H. Choi, Glen C. King, and James R. Elliott, “New Rhombohedral Alignment of Cubic Semiconductor On Trigonal Substrate At A High Temperature”, NASA Case No. LAR-17553-1, July 10, 2007. [patent filed on September 5, 2008] Yeonjoon Park, Sang H. Choi, and Glen C. King, “Epitaxial Growth of Group IV Semiconductor Alloys on Basal Plane of Trigonal or Hexagonal Crystal”, Invention Disclosure, NASA Case No. LAR 17185-1, June 13, 2005. [patent filed on July 13, 2006]

Yeonjoon Park, Sang H. Choi, Glen C. King, and James R. Elliott “Supporting XRD DATA for rhombohedrally-grown diamond-structured group-IV alloys on basal plane of trigonal substrate”, NASA Case No. LAR 17392-1, June 28, 2006. [patent filed on September 5, 2008] Yeonjoon Park, Sang H. Choi, and Glen C. King, “Lattice Matched SiGe Layer on Single Crystalline Sapphire Substrate”, Invention Disclosure, NASA Case No. LAR 16868-1, February 26, 2004. [patent filed on April 23, 2007] Yeonjoon Park, Sang H. Choi, and Glen C. King, “Silicon Germanium Semiconductive Alloy And Method Of Fabricating Same”, U.S. Patent No. 7,341,883, March 11, 2008 Yeonjoon Park, Sang H. Choi, Glen C. King, James Elliott, Diane M. Stoakley, “Graded Indexed SiGe Layers on Lattice Matched SiGe Layers on Sapphire”, U.S. Patent No. 7,514,726 B2, April 7, 2009 Yeonjoon Park, Glen C. King, and Sang H. Choi, “Highly [111]-oriented SiGe layer on c- plane sapphire”, Journal of Crystal Growth, Vol. 310, Issue 11, p2724~2731, May 15, 2008.

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