Tensile Ge microstructures for lasing fabricated by means of a silicon complementary metal-oxide-semiconductor process

Abstract

In this work we study, using experiments and theoretical modeling, the mechanical and optical properties of tensile strained Ge microstructures directly fabricated in a state-of-the art complementary metal-oxide-semiconductor fabrication line, using fully qualified materials and methods. We show that these microstructures can be used as active lasing materials in mm-long Fabry-Perot cavities, taking advantage of strain-enhanced direct band gap recombination. The results of our study can be realistically applied to the fabrication of a prototype platform for monolithic integration of near infrared laser sources for silicon photonics.

Extending the emission wavelength of Ge nanopillars to 225 μm using silicon nitride stressors

“…As expected, strain appeared to increase in smaller samples for a given stressor layer, as the stress in the film can transfer more fully into the underlying structure. Increased strain in smaller structures has indeed been reported elsewhere [17]. As discussed previously, with carrier diffusion throughout the structure, the larger total shift of the spectra, compared to the broadening seen with the 300 nm pillars could be a hallmark of more uniform strain.…”

“…Optical emission from strained Ge has been demonstrated in a number of ways, for example, with mechanically strained membranes [11], micro-machined structures [12], micro bridge structures [13], and silicon nitride stressor layers applied to Ge microdisks [14,15] and Ge waveguides [16,17]. The use of silicon nitride as a stressor layer is especially interesting, as it is already used in CMOS processes for strained Si channels, and therefore it is of interest to investigate the limits of this approach.…”

Analysis of Ge micro-cavities with in-plane tensile strains above 2 %

“…Electron concentrations are calculated by Fermi-Dirac integrals, and the band structure has been calculated using an effective mass method, which does not take into account the non-parobolicity caused by strain. It should be noted, that this effect has been demonstrated experimentally in waveguides [12] with different orientations, but the presence of such strains in micro-disk and micro-ring geometries have not been considered in previous works, and has to be considered to fully understand the gain available from such cavities. The exact degradation of gain will of course require knowledge of the optical overlap of the mode with the strain distribution in the micro-disk.…”

“…Subsequently, high levels of strain have been demonstrated in micro bridge structures [11], and free standing membranes. Silicon nitride stressors have also been used to demonstrate high levels of strain in waveguides [12], pillar structures [13], and Ge micro-disks [14,15].…”

Extended Defect Propagation in Highly Tensile-Strained Ge Waveguides

“…Real-time defect generation observed in transmission electron microscopy (TEM) was then correlated with strain distribution analysis, Raman spectroscopy, and photoluminescence (PL). Tensile strain with a strong hydrostatic component was induced in Ge waveguides by compressive SiN x stress liners [27,28], which are widely used for strained complementary metal oxide semiconductor (CMOS) transistors. In a wraparound geometry, as shown in Figure 1, compressive stress in the SiN x induces significant tensile strain up to 3.6% in the Ge along two dimensions, just as planar biaxial strain techniques would do.…”