Overview

The advances in crystal growth technologies, such as molecular beam epitaxy, gas-source molecular beam epitaxy (GSMBE), organometallic vapor phase epitaxy (OMVPE) and chemical vapor deposition (CVD) have enabled ultrathin epitaxial semiconductor layers to be routinely grown with both monolayer precision in thickness and composition control to about 1 at%. Major advances have been achieved in binary SiGe alloys where the built-in strain and the composition of a pseudomorphic Si _{1 ? x}Ge _x layer on a Si substrate affect the band structure, energy gap as well as the band offset significantly. High performance devices and circuits based on Si/Si _{1 ? x}Ge _x heterostructures have been demonstrated. There is now a substantial literature on various aspects of Si _{1 ? x}Ge _x epitaxial growth and devices and a number of review articles treating various aspects [1 4].

Many methods have been used for deposition of epitaxial Si and alloys incorporating Ge, C and Sn on Si substrates. These can be broadly categorized into physical vapor deposition and chemical vapor deposition methods. The main physical vapor deposition method is MBE which is widely used because of its excellent control over thickness and composition of layers. Chemical vapor deposition methods are now available for the growth of very high quality strained layers. Notable among them are: limited reaction processing CVD (LRPCVD) [5], rapid thermal chemical vapor deposition (RTCVD) and low temperature ultra high vacuum chemical vapor deposition (UHVCVD) [6]. Gibbons and his group at Stanford were...