Germanium-rich silicon-germanium materials for field-effect modular application
Germanium rich silicon germanium materials for field effect modular application
Massachusetts Institute of Technology. Dept. of Materials Science and Engineering.
Lionel C. Kimerling.
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The development of electric-field-induced optical modulation in the materials capable of monolithically integrated on silicon (Si) substrates offer the possibility of high-speed modulation in a pico second timeframe as well as low power consumption, key requirements for integrated modulator applications. This thesis presents a study of the Franz-Keldysh effect in germanium (Ge) layers epitaxially grown on Si substrates, by using free-space spectral responsivity measurement. Generalized Franz-Keldysh formalism and separately measured Ge material constants were used to calculate theoretical results, which were in agreement with experimental data. The Franz-Keldysh model predicts that the Ge layers on Si substrates will be the best material for phase modulation at nearly 2 [mu]m wavelength, with a value of L, of 3.8 mm and insertion loss of 0.4 dB. In addition, this thesis presents the design of silicon-germanium (SixGe1-x) electroabsorption and phase modulators at 1.55 pLm wavelength from the Franz-Keldysh model. The composition optimized for electroabsorption and phase modulator applications is SixGe1-x with a value of x~0.075 and 0.135, respectively. To achieve high-quality Ge-rich SiGe materials for the modulator applications, deposition of SixGe1-x (0.008<x<0.125) buffers at low temperature was performed, and the growth kinetic was studied. The films were deposited on SiGe buffers to reduce lattice mismatch between the buffers and the remainders of the films, and were in-situ annealed in the same condition as was used for similarly grown Ge films for a reduction of threading dislocation density. Si0.15Ge0.85 p-i-n diodes and Sio.15Geo.ss rib waveguides were fabricated.(cont.) High leakage current in the Si0.15Ge0.85 p-i-n diodes was due to dislocation defects consistent with measured threading dislocation density from PV-TEM images, which showed threading dislocation density of approximately 1.5±0.5 x 109 cm-2. The analysis shows that threading dislocation density below 5 x 107 cm-2 is required for high performance of p-i-n diodes. Furthermore, high optical loss was measured in Si0.15Ge0.85 rib waveguides and strip-load waveguides. The loss is due to light scattering at sidewalls and dislocations. Scattering from dislocations less than 1 x 108 cm-2 is required for loss below materials' interband absorption. This high threading dislocation density shows that the annealing condition used for Ge-on-Si is not effective in reduction of threading dislocation density in Si0.15Ge0.85. Si solutes/dislocations interactions in Si0.15Ge0.85 reduce glide velocity of dislocations as well as the possibility that dislocations run into and annihilate one another.
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.Includes bibliographical references (p. 107-111).
DepartmentMassachusetts Institute of Technology. Dept. of Materials Science and Engineering.
Massachusetts Institute of Technology
Materials Science and Engineering.