Properties and devices of SiGe heterostructures and superlattices

Several successful techniques for growth of pseudomorphic strained Ge_xSi_1-x layers on Si are briefly reviewed. The properties of the strained layers that affect the device design and performance are discussed. Devices based on the material are also discussed, with emphasis on heterojunction bipolar transistors (HBTs). High gain and high cutoff frequency has been predicted. Other advances, including the demonstration of tunneling structures, quantum well structures, and devices based on band-aligned superlattices, are presented. The growth of monolayer Ge_mSi_n superlattices is discussed as well as the concept of Brillouin zone-folding and the formation of quasi-direct bandgaps