Toward a Germanium Laser for Integrated Silicon Photonics

Group IV Direct Band Gap Photonics: Methods, Challenges, and Opportunities

“…It arises due to the difference between the thermal expansion coefficients of Si and Ge . High n-doping is introduced to fill the parasitic indirect states (Xiaochen et al, 2010). Such doping does not transform the material into a direct gap system, but it appeared that under optical excitation and electrical pumping the light emission shows an intensity threshold as well as linewidth narrowing Camacho-Aguilera et al, 2012).…”

High phosphorous doped germanium: Dopant diffusion and modeling

“…An optically pumped Ge laser at room temperature has been demonstrated with 50 cm À1 gain using a phosphorous concentration of 1 Â 10 19 cm À3 . 6 Since theoretical calculations predict that the Ge material gain increases with doping concentration, 7 higher doping concentrations are advantageous for electrical pumping to overcome additional losses due to free carrier absorption in highly doped contact layers and at metal interfaces.…”

Optimum strain configurations for carrier injection in near infrared Ge lasers

“…1 Recent studies showed that Ge has the potential for monolithic integration on Si substrate, hence such devices would have a lower fabrication cost than III-V semiconductors. 2,3 At room temperature the emitted light from the direct bandgap (C-valley) transitions in Ge is in the near infrared wavelength range, but the direct bandgap is $140 meV above the indirect bandgap, 1 a feature that makes it a poor light-emitting material. However, the band structure of Ge can be engineered by tensile strain: the direct bandgap decreases, the degenerate equivalent indirect valleys (X and L) shift in energy and might split, and the degeneracy of the heavy hole (HH) and light hole (LH) valence bands is lifted, depending on the type of the applied strain and its direction, as well as the substrate orientation.…”