The preparation of GeSn quantum dots (QDs) facilitates the solution of Si-based light source for communication. The GeSn QDs with a uniform size of 5 nm embedded in amorphous GeSn were synthesized by low temperature annealing on amorphous GeSn strips intersected with Sn strips. The Sn fraction in GeSn QDs is much higher than that in original amorphous GeSn matrix. A novel growth mechanism related to Sn diffusion induced nucleation and the strain limitation effect was proposed. The direct bandgap of ∼0.8 eV extracted from room-temperature photoluminescence and absorption spectra is larger than the theoretical prediction of 0.41 eV in bulk GeSn with Sn fraction of 13.6%.
High‐performance polycrystalline GeSn (poly‐GeSn) junctionless thin‐film transistors (JL‐TFTs) are proposed and fabricated at low process temperatures. Poly‐GeSn thin films with a Sn fraction of 4.8% are prepared using cosputtering and pulsed laser annealing (PLA) techniques. The ultra‐rapid nonequilibrium thermodynamic process with 25 ns PLA renders a good crystal GeSn thin film at a low temperature. The ION/IOFF ratio increases by three orders of magnitude with GeSn channel thickness varying from 60 to 10 nm, suggesting that switch‐off current is dominated by depletion width. A superior effective mobility of 54 cm2 V−1 s−1 is achieved for the JL‐TFT with a 10 nm‐thick GeSn film as a consequence of gate/channel interface passivation by oxygen plasma.
Polycrystalline Ge 1−x Sn x (poly-Ge 1−x Sn x ) alloy thin films with high Sn content (> 10%) were fabricated by cosputtering amorphous GeSn (a-GeSn) on Ge (100) wafers and subsequently pulsed laser annealing with laser energy density in the range of 250 mJ/cm 2 to 550 mJ/cm 2 . High quality poly-crystal Ge 0.90 Sn 0.10 and Ge 0.82 Sn 0.18 films with average grain sizes of 94 nm and 54 nm were obtained, respectively. Sn segregation at the grain boundaries makes Sn content in the poly-GeSn alloys slightly less than that in the corresponding primary a-GeSn. The crystalline grain size is reduced with the increase of the laser energy density or higher Sn content in the primary a-GeSn films due to the booming of nucleation numbers. The Raman peak shift of Ge-Ge mode in the poly crystalline GeSn can be attributed to Sn substitution, strain, and disorder. The dependence of Raman peak shift of the Ge-Ge mode caused by strain and disorder in GeSn films on full-width at half-maximum (FWHM) is well quantified by a linear relationship, which provides an effective method to evaluate the quality of poly-Ge 1− x Sn x by Raman spectra.
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