High-resolution X-ray diffraction reciprocal space mapping around (004) reflection. The germanium film is 250 nm thick and was grown on an InGaAs buffer layer with an effective indium content of 13%. The diffraction spots correspond to Ge, GaAs, and InGaAs from top to bottom. (a) X-ray reciprocal space mapping around (004), in-plane azimuthal direction: 180°. (b) X-ray reciprocal mapping around (004), azimuthal direction 90°.
Raman measurements showing the shift of the Ge-Ge phonon vibration. The thickness of the Ge layer and the indium composition of the buffer layer are indicated on the graph.
Room temperature photoluminescence for 25 nm (a), 100 nm (b), 150 nm (c), and 200 nm (d) thick germanium films grown on InGaAs buffer layers with various indium contents. The effective indium content is indicated on the graphs. The effective indium content accounts for the partial relaxation of the buffer layer. The curves have been normalized and offset for clarity. The luminescence is excited by a He-Ne laser. The small resonance around 1350 nm is a defect signal from the InGaAs buffer layer.
Comparison between the resonance wavelength of the direct band gap recombination and the one calculated using a 30 band formalism. The calculated resonances of recombination involving heavy holes and light holes are indicated as full lines. The scattered points correspond to the experimental data extracted from Fig. 3 .
(a) Room temperature photoluminescence spectra of germanium on In0.112Ga0.888As for an increasing thickness from 100 to 300 nm. The curves have been offset for clarity. The Ge thicknesses are indicated in the figure. The small resonance at 1330 nm clearly observed on the 100 and 150 nm thick layers are defect signals from the InGaAs buffer layer. (b) Photoluminescence amplitude as a function of thickness for 11.2% indium buffer. The experimental data are represented by squares. The full line is a fit accounting for bulk and surface recombination.
Biaxial strain magnitude deduced from photoluminescence measurements as a function of germanium thickness and effective indium content. The height of the bars is proportional to the in-plain strain. The shaded area highlights the zone where strong relaxation has occurred. The black arrows indicate a significant decrease in the photoluminescence amplitude.
Comparison of biaxial strain deduced from Raman (dots), microphotoluminescence (squares), and X-ray diffraction measurements (triangles). The horizontal axis shows a combination of indium content of the buffer layer (%) and germanium thickness (nm). The bar for the X-ray measurement of the 13%−250 nm sample highlights the values deduced for two in-plane perpendicular directions (0.39% and 0.21%, average value 0.3%).
Average lattice parameters for a 250 nm thick Ge sample grown on a 1 μm thick InGaAs buffer layer with a 13% effective indium content. All values are in nm.
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