Systematic Investigation of Photoluminescence Characteristics in GeSn Films with Varied Sn Content by High-Resolution and Wide-Spectrum System

The Ge1-xSnx alloy is a promising candidate for silicon-based optoelectronic devices, yet few experimental studies have investigated its full indirect-to-direct bandgap transition behavior. The photoluminescence (PL) characteristics of Ge1-xSnx films with Sn compositions of 3.3 %, 6.5 %, 10.3 %, and 12.8 % were investigated by a high-resolution and wide spectrum (1 similar to 5.5 mu m) Fourier Transform Infrared Spectrometer PL system. Owing to the wide spectrum measurement capability, the PL spectra of these Ge1-xSnx films can be compared in a single system. It can be seen that the PL spectrum of the high-Sn content GeSn film (12.8 %) exhibits a high-energy shoulder peak, which is different from the low-Sn content GeSn film (3.3 %) with a low-energy shoulder peak. By extracting the transition peak position through Gaussian fitting, we observed for the first time that the direct bandgap energy of the high-Sn content GeSn is lower than the indirect bandgap energy, resulting in the negative energy separation. Furthermore, as the Sn content increases, a clear indirect-to-direct transition is observed, which leads to opposite temperature-dependent PL-intensity trends between the high- and low-component GeSn films. Finally, the insensitivity to temperature was demonstrated in GeSn with Sn compositions of 6.5 %, indicating a balance between radiative and non-radiative recombination. These findings provide further evidence of T-and L-valley inversion and quasi-direct bandgap GeSn materials, indicating great potential for direct bandgap GeSn and GeSn based optoelectronic devices grown on Si.