Dislocation-free strain-engineered silicon and silicon-germanium nanomembranes

Strain-engineered Si and SiGe have been widely used in industry and academia due to their highly desirable properties, such as the increased mobility and the ability to confine charge carriers. The conventional method of strain engineering Si and SiGe is prone to dislocations and strain non-uniformity. Researchers have developed new methods that are not prone to these problems, and elastically-strained Si nanomembranes is one such method. The method is achieved by first growing pseudomorphic Si/SiGe/Si layers (trilayer) on Si on insulator (SOI) substrate. The trilayer is dislocation-free because the layers are grown below the critical thickness. Upon selective removal of the insulator layer, elastic strain-sharing occurs which partially relaxes the compressive strain in SiGe layer and tensilely strains the Si layers. Dislocation-free, smooth 0.6% strained Si nanomembranes had been obtained.;This dissertation involves the investigation of the challenges in using the nanomembranes elastic strain-sharing method to achieve higher strain. Solution to the challenges were developed and explained. A new method of strain-engineering using nanomembranes was developed and was experimentally proven to yield dislocation-free fully-relaxed SiGe 33%. Plan-view Transverse Electron Microscopy (TEM) shows that the SiGe nanomembranes (SiGeNM) is completely misfit-dislocation free. Raman and Xray diffraction (XRD) confirm that the SiGe is fully relaxed. Atomic Force Microscopy (AFM) shows that the back surface of the SiGeNM is smooth (0.27 nm Root Mean Square [RMS] roughness). Pseudomorphic growth of 35 nm strained Si on the back surface of SiGeNM yields 1.2% smooth strained Si.