Ge(1-x)Sn(x) alloy synthesized by ion-implantation: from epitaxial thin films to crystalline nanostructures

Group IV semiconductor alloys have drawn substantial attention for their potential applications in optoelectronic devices capable of integration with the existing silicon-based IC circuitry. Monocrystalline Ge1-xSnx alloys are promising for electronic and optical applications in virtue of their high carrier mobility and possibility of direct bandgap transition.
In this contribution we present the monocrystalline Ge1-xSnx thin film and nanostructure synthesized by ion implantation, by which the low solubility of Sn in Ge can be overcome. Sn was implanted into commercial Ge wafers at room temperature. After implantation, cross-sectional transmission electron microscopy (TEM) image reveals a 70 nm thick Sn-doped porous structure on 80 nm thick Sn-doped amorphous Ge layer. The implantation induced amorphized layer has been recrystallized after ultrashort thermal process. By nanosecond pulsed laser melting (PLM), high quality monocrystalline Ge1-xSnx thin films were obtained through a bottom-up liquid phase epitaxial process. On the other hand, solid phase recrystallization induced by millisecond flash lamp annealing (FLA) results in crystalline Ge1-xSnx porous nanostructures. Depending on the FLA condition, the structure can be polycrystalline or monocrystalline.
Field emission scanning electron microscopy was applied to measure the surface morphology. High resolution transmission electron microscopy and Rutherford backscattering and channeling analysis confirmed the monocrystalline structure of the Ge1-xSnx layer. The crystallinity and the lattice expansion due to Sn doping were determined by X-ray diffraction and micro-Raman spectroscopy. Our investigation provides an efficient, IC-compatible technique to prepare high quality monocrystalline Ge1-xSnx alloys.