Lasing is experimentally demonstrated in a direct bandgap GeSn alloy, grown directly onto Si(001). The authors observe a clear lasing threshold as well as linewidth narrowing at low temperatures.

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Lasing in direct-bandgap GeSn alloy grown on Si

Hybrid silicon lasers based on bonded III–V layers on silicon are currently the best contenders for on-chip lasers for silicon photonics. On-chip silicon light sources are highly desired for use as electrical-to-optical converters in silicon-based photonics. Zhiping Zhou and Bing Yin of Peking University in China and Jurgen Michel of Massachusetts Institute of Technology assess the three main contenders for such light sources: erbium-based light sources, germanium-on-silicon lasers and III-V-based silicon lasers. They consider operating wavelength, pumping conditions, power consumption, thermal stability and fabrication process. The scientists regard the power efficiencies of electrically pumped erbium-based lasers as being too low and the threshold currents of germanium lasers as being too high. They conclude that III–V quantum dot lasers monolithically grown on silicon show the most promise for realizing on-chip lasers.

/pdf/on-chip-light-sources-for-silicon-photonics-ky23qv18q4.pdf

On-chip light sources for silicon photonics

GeSn is predicted to exhibit an indirect to direct band gap transition at alloy Sn composition of 6.5% and biaxial strain effects are investigated in order to further optimize GeSn band structure for optoelectronics and high speed electronic devices. A theoretical model has been developed based on the nonlocal empirical pseudopotential method to determine the electronic band structure of germanium tin (GeSn) alloys. Modifications to the virtual crystal potential accounting for disorder induced potential fluctuations are incorporated to reproduce the large direct band gap bowing observed in GeSn alloys.

Achieving direct band gap in germanium through integration of Sn alloying and external strain

This work investigates the electronic band structures of bulk Ge1-xSnx alloys using the empirical pseudopotential method (EPM) for Sn composition x varying from 0 to 0.2. The adjustable form factors of EPM were tuned in order to reproduce the band features that agree well with the reported experimental data. Based on the adjusted pseudopotential form factors, the band structures of Ge1-xSnx alloys were calculated along high symmetry lines in the Brillouin zone. The effective masses at the band edges were extracted by using a parabolic line fit. The bowing parameters of hole and electron effective masses were then derived by fitting the effective mass at different Sn compositions by a quadratic polynomial. The hole and electron effective mass were examined for bulk Ge1-xSnx alloys along specific directions or orientations on various crystal planes. In addition, employing the effective-mass Hamiltonian for diamond semiconductor, band edge dispersion at the Γ-point calculated by 8-band k.p. method was fitted...

/pdf/electronic-band-structure-and-effective-mass-parameters-of-q3mvcv2nt9.pdf

Electronic band structure and effective mass parameters of Ge1-xSnx alloys

Si–Ge–Sn alloys: From growth to applications

We synthesized up to Ge0.914Sn0.086 alloys on (100) GaAs/InyGa1−yAs buffer layers using molecular beam epitaxy. The buffer layers enable engineered control of strain in the Ge1−xSnx layers to reduce strain-related defects and precipitation. Samples grown under similar conditions show a monotonic increase in the integrated photoluminescence (PL) intensity as the Sn composition is increased, indicating changes in the bandstructure favorable for optoelectronics. We account for bandgap changes from strain and composition to determine a direct bandgap bowing parameter of b = 2.1 ± 0.1. According to our models, these are the first Ge1−xSnx samples that are both direct-bandgap and exhibit PL.

Charles Hitzman

Papers

Increased photoluminescence of strain-reduced, high-Sn composition Ge1−xSnx alloys grown by molecular beam epitaxy