High-Ge-Content SiGe Alloy Single Crystals Using the Nanomembrane Platform.

The growth of single crystals of Ge-rich SiGe alloys in an extended composition range is demonstrated using the nanomembrane (NM) platform and III-V growth substrates. Thin films of high-Ge-content SiGe films are grown on GaAs(001) to below the kinetic critical thickness and released from the growth substrate by selectively etching a release layer to relax the strain. The resulting crystalline nanomembranes at the natural lattice constant of the alloy are transferred to a new host and epitaxially overgrown at similar compositions to make a thicker single crystal. Straightforward critical-thickness calculations demonstrate that a very wide range of Group IV alloys, including those involving Sn, can be fabricated using the NM platform and the proper choice of III-V substrate. Motivations for making new Group IV alloys center on band gap engineering for the development of novel Group IV optoelectronic structures and devices.