Optical Characterization of Si-Based Ge1−x Sn x Alloys with Sn Compositions up to 12%
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Optical properties of germanium tin (Ge1−x Sn x ) alloys have been comprehensively studied with Sn compositions from 0 (Ge) to 12%. Raman spectra of the GeSn samples with various Sn compositions were measured. The room temperature photoluminescence (PL) spectra show a gradual shift of emission peaks towards longer wavelength as Sn composition increases. Temperature dependent PL shows the PL intensity variation along with the temperature change, which reveals the indirectness or directness of the bandgap of the material. As temperature decreases, the PL intensity decreases with Sn composition less than 8%, indicating the indirect bandgap Ge1−x Sn x ; while the PL intensity increases with Sn composition higher than 10%, implying the direct bandgap Ge1−x Sn x . Moreover, the PL study of n-doped samples shows bandgap narrowing compared to the unintentionally (Boron) doped thin film with similar Sn compositions due to the doping.
KeywordsGeSn alloy n- doped GeSn Raman spectroscopy photoluminescence
The work in UA is supported by the National Science Foundation (NSF) under EPS-1003970, Defense Advanced Research Projects Agency (DARPA) under W911NF-13-1-0196,the Arktonics, LLC (Air Force SBIR) under FA9550-14-C-0044 and Air Force Office of Scientific Research (AFOSR) under FA9550-14-1-0205. Drs. R. A. Soref and G. Sun acknowledge support from AFOSR under FA9550-14-1-0196.
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