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Scanning electron microscopy images of an unstrained (a)-left and a tensile-strained (b)-right germanium microdisks. The pedestal is in GaAs while the disk is in germanium. The stressor is a silicon nitride film deposited after microdisk processing.
(a) Room temperature photoluminescence spectra of an unstrained (bottom curve) or tensile-strained (top curve) 4 μm diameter microdisk. The dots correspond to the calculated spectral positions of Fabry-Perot (FP) modes for the unstrained microdisk. The assignment of FP modes with the broad resonances is highlighted by the vertical dashed lines. (b) Zoom of the emission for the unstrained disk around 1740 nm. (c) Zoom of the emission for the tensile-strained disk around 2015 nm, after baseline subtraction. The grey solid curves correspond to Lorentzian fits. One observes whispering gallery modes in both structures. The Q factors for modes at 1744 and 1998 nm, indicated by arrows, are around 1350 and 1000.
Room temperature photoluminescence spectra of tensile-strained germanium microdisks for three different disk diameters. The spectra have been offset for clarity.
Finite element modeling of the strain profile for a 4 μm diameter disk with a 1 μm pedestal. (a) Cross-section representing the radial component of the strain field. Only half of the structure is represented. The black solid lines are guides to the eye to distinguish the different layers. The color bar indicates the strain amplitude. (b) Amplitude of the strain field calculated at the disk center as a function of the vertical direction for different pedestal diameters. 0 corresponds to the interface between Ge and GaAs, 0.3 corresponds to the Ge/nitride interface.
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