Abstract
Ge on Si micro-disk, ring and racetrack cavities are fabricated and strained using silicon nitride stressor layers. Photoluminescence measurements demonstrate emission at wavelengths ≥ 2.3 μm, and the highest strained samples demonstrate in-plane, tensile strains of > 2 %, as measured by Raman spectroscopy. Strain analysis of the micro-disk structures demonstrate that shear strains are present in circular cavities, which can detrimentally effect the carrier concentration for direct band transitions. The advantages and disadvantages of each type of proposed cavity structure are discussed.
Highlights
There has been significant interest in materials which are compatible with silicon foundry manufacture, such as strained Ge, that can be integrated into Si technology to allow expansion into new markets, such as Si photonics in the near-infrared (NIR) [1] and the mid-infrared (MIR)[2, 3, 4] parts of the electromagnetic spectrum
A reference sample was fabricated with an undercut wet etch but with a silicon nitride film with negligible stress, which was used for photoluminescence (PL) and Raman spectroscopy measurements, to confirm the absence of significant heating from the laser
Undercut Ge micro-cavities, including micro-disks, micro-rings, and race-track structures were fabricated using a combination of dry etching, and wet etching in tetramethylammonium hydroxide (TMAH)
Summary
There has been significant interest in materials which are compatible with silicon foundry manufacture, such as strained Ge, that can be integrated into Si technology to allow expansion into new markets, such as Si photonics in the near-infrared (NIR) [1] and the mid-infrared (MIR)[2, 3, 4] parts of the electromagnetic spectrum. Tensile strain has been demonstrated to decrease the difference between the direct and indirect bandgaps, enhancing the poor radiative recombination efficiency of the material by increasing the direct bandgap contribution This approach has the potential to reduce the lasing thresholds in strained Ge lasers [6], compared to the optically and electrically pumped lasers previously demonstrated with low levels of tensile strain [7, 8]. In GeSn alloys, the Γ to L difference can be further enhanced to increase the electron concentration at the Γ point, and allow the potential for room temperature lasing. Silicon nitride stressors have been used to demonstrate high levels of strain in waveguides [12], pillar structures [13], and Ge micro-disks [14, 15]. The improvements to the strain profile are confirmed using micro-Raman spectroscopy for analysis of the strain
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