Synthesis of GeSn alloys by sputter deposition and Pulsed Laser Melting

The realization of high Sn content Ge1-ySny alloys has been the center of numerous research studies over the last two decades. The reason for this lies in the fact that a Sn concentration higher than the solid solubility limit (1 at. %) lowers the Ge conduction band minima until reaching the crossover from indirect to direct bandgap. Tensile strain is also useful since it decreases the necessary Sn concentration for the bandgap transition. In this way, a direct bandgap material with an absorption range in the Short Wavelength Infra-Red (SWIR) region can be obtained, useful for optoelectronic applications such as photodetectors. In the present research work Ge1-ySny alloys were fabricated on Ge-buffered Si (001) substrates by a novel ex-situ approach consisting in Sn sputter deposition followed by pulsed laser annealing (i.e. Pulsed Laser Melting - PLM). Samples were realized by 8 or 12 min deposition time and irradiated with 1 or 8 laser pulses at 800 mJ/cm2. A samples’ subset was also subjected to an extra laser pulse at lower energy density (between 300 and 400 mJ/cm2) in order to increase the substitutional Sn fraction. The strong out-of-equilibrium conditions of PLM allowed to realize GeSn alloys with Sn content up to 21 at. %. The samples were characterized via Secondary Ion Mass Spectrometry (SIMS), High Resolution X-Ray Diffraction (HRXRD), Raman spectroscopy and Atomic Force Microscopy (AFM). The work presented here sets the basis for the realization of dual band photodetectors working in the SWIR and VIS ranges.