A micromachining-based technology for enhancing germanium light emission via tensile strain

Ge-on-Si photonic devices for photonic-electronic integration on a Si platform

“…In a Fabry-Perot resonator of Ge waveguide, a lasing was also reported under an optical pumping [54] and an electrical pumping [55,56], although there is no further report to obtain the lasing. In order to generate a large (> 1%) tensile strain towards direct-gap Ge, an application of micromechanical stress [57] to membrane structures [58,59,60,61] was examined, but no lasing has been obtained yet. Critical process techniques might be required for the laser operation, and further studies are necessary from the viewpoints of material science and device physics.…”

Enhanced light emission from improved homogeneity in biaxially suspended Germanium membranes from curvature optimization

“…While this strain can be a useful starting point, it is not enough to reduce threshold current density to a practical level. Other methods include depositing nitride stressor layers [16][17][18][19], suspending silicon dioxide and then transferring the strain into Ge micro disks [20,21] and suspending Germanium directly (the focus of this paper) [22][23][24][25][26][27][28][29][30].Suspended structures amplify the small amounts of tensile biaxial strain introduced during the epitaxial growth of Ge on Si. Certain regions of the Ge are suspended in which the membrane constricts resulting in an enhancement of the tensile strain, and the regions which are still tethered to the rest of the wafer (referred to as pads) relax resulting in a compressive strain.…”

“…Suspension is generally achieved by dry etching 'windows' into the wafer and then using a wet etchant to under etch the substrate underneath thus suspending the Ge. By controlling the geometry of these etchant windows, both uniaxial and biaxial tensile strain can be introduced to the central region of the membrane [22].…”

“…This discrepancy was accredited to be due to the unfavorable strain profiles confining carriers to the highly strained corner regions acting as a parasitic mechanism reducing the observed PL intensity. Jain et al [22] used a combination on suspended Ge membranes as well as silicon nitride layers on the pads to enhance the strain reporting a large biaxial strain of 0.8% in an extremely large area of 40 μm 2 . The observed PL enhancement was extremely large at 260 X likely due to the thermal effects and large area, the excited carriers cannot diffuse such great lengths and therefore the corner strain regions become inconsequential.…”

Quantum cascade lasers grown on silicon

“…While various Si-based modulators and photodetectors have already been demonstrated [2][3][4][5] , integrated light sources have for long remained a challenge 6 . Silicon-based sources would straight away bridge the gap but the indirect bandgap of Si or Ge is a severe limitation and, in spite of unquestionable advances [7][8][9][10] , such devices will not outperform in the foreseeable future their III-V semiconductor counterparts which remain the most efficient semiconductor laser technology. Much work has thus been devoted in the last decade to integrating III-V laser diodes on Si platforms for telecom applications.…”