Photoluminescence spectroscopy of GeSn alloys grown on Ge-on-Si virtual substrates

Silicon (Si) based devices have dominated the electronics industry over the past decades but is not suitable for making lasers due to its optical properties. As an indirect bandgap semiconductor, Si has inefficient optical emission, and therefore cannot be used to make a light source on a Si chip. As an alternative, germanium (Ge) can be grown on Si and is currently being used for photonic devices. Like Si, Ge is an indirect bandgap material, but it exhibits direct band gap emission at room temperature. Ge can also be band engineered through strain and alloying with tin (Sn) to create a directbandgap material. Recent research has focused on creating a Ge/GeSn laser diode that can operate at room temperature. Though progress has been made, GeSn still suffers from low intensity with increasing Sn due to high defect densities causing nonradiative recombination.

In this work, we studied GeSn samples with varying Sn content that were grown on Ge-buffered-Si (virtual substrate) using chemical vapor deposition (CVD). The structural properties of the materials were studied using Rutherford backscattering, high-resolution X-ray diffraction and cross-sectional transmission electron microscopy. Finally, we studied the optical emission using photoluminescence (PL) spectroscopy.