Mid-infrared emission of germanium-tin films produced by sputtering

In this work, the synthesis of germanium-tin (GeSn) films by magnetron sputtering is reported. A fractional factorial experiment was conducted; the varied factors were temperature, power applied to Ge target by a radio-frequency source, and power applied to the Sn target by a direct-current source. Vibrational modes, film composition, morphology, deposition rate, dark conductivity, Raman spectra, and Fourier-transform infrared (FTIR) spectra of the GeSn films were analyzed. Mid-infrared spectrum of emission and absorption was obtained by FTIR electroluminescence (EL) spectroscopy in the range of 400– $4000 cm − 1$⁠, thermal emission was monitored by a FLIR camera in the range of 8– $14μ m$⁠, and power emitted from the GeSn films was measured in the range of 2.7– $5.3μ m$ by means of a InAsSb photodetector; results obtained by these approaches at room temperature and low-field bias were consistent. Sample Ge $0.71$Sn $0.29$ exhibited Ge Raman crystalline fraction of 85%; from FTIR EL spectrum were observed peaks of absorption located at 1084, and 606  $cm − 1$ that was attributed to $Si − Si$ bonds from the c-Si substrate, as well as broadband attenuation of 2% in the range of $1500−3500 cm − 1$⁠, this behavior was associated to the self-heating of this sample at 90  $°$C. Sample Ge $0.3$Sn $0.7$ showed Raman crystalline fraction of 16 and 22% for Ge and Sn, respectively; from FTIR EL spectrum were observed peaks of emission located at 2.74  $μ m$ (0.452 eV) and 6.66  $μ m$ (0.186 eV), as well as broadband emission in the range of 600–2000  $cm − 1$ attributed to Planck’s law at a temperature of 45  $°$C; these results were correlated to the proper content of Ge and Sn, fluctuating current, and polymorphic morphology of this sample.