Investigation of Ge1-xSnx/Ge quantum well structures as optical gain media

An efficient Si-based laser is one of the most important components for photonic integrated circuits to break the bottleneck of data transport over optical networks. The main challenge is to create gain media based on group-IV semiconductors. Here we present an investigation of using low-dimensional Ge1-xSnx/Ge quantum-well (QW) structures pseudomorphically grown on Ge-buffered Si substrates as optical gain media for efficient Si-based lasers. Epitaxial growth of Ge1-xSnx/Ge QW structures on Ge-buffer Si substrate was carried out using low-temperature molecular beam epitaxy techniques. The light emission properties of the grown Ge1-xSnx/Ge QW structure were studied using photoluminescence spectroscopy, and clear redshifts of emission peaks were observed. Theoretical analysis of band structures indicates that Ge1-xSnx well sandwiched by Ge barriers can form type-I alignment at Gamma point with a sufficient potential barrier height to confine carriers in the Ge1-xSnx well, thereby enhancing efficient electron-hole direct recombination. Our calculations also show that the energy difference between the lowest Gamma-conduction subband and L-conduction subband can be reduced with increasing Sn content, thereby enabling optical gain. These results suggest that Ge1-xSnx/Ge QW structures are promising for optical gain media to develop efficient Si-based light emitters.