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

Abstract

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 400–4000cm−1, thermal emission was monitored by a FLIR camera in the range of 8–14μm, and power emitted from the GeSn films was measured in the range of 2.7–5.3μm by means of a InAsSb photodetector; results obtained by these approaches at room temperature and low-field bias were consistent. Sample Ge0.71Sn0.29 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 1500−3500cm−1, this behavior was associated to the self-heating of this sample at 90 °C. Sample Ge0.3Sn0.7 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 μm (0.452 eV) and 6.66 μm (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.