UBC Theses and Dissertations
Monolithic integration of AlGaAs distributed Bragg reflectors on virtual Ge substrates via aspect ratio trapping Lin, Yiheng
Over the past two decades, researchers have devoted great efforts on Si photonics to overcome the communication bottleneck of integrated circuits. In order to realize short-reach optical interconnects, excellent performance has been achieved so far on waveguides, modulators and detectors, which use Si compatible materials (e.g. SiO₂, Si₃N₄ and SiGe) and processes. However, lasers on Si have been much more difficult to implement. Monolithically integrated vertical cavity surface emitting laser (VCSEL) on Si platforms are a suitable choice as output devices on Si, and is the long-term goal of this project. The research for this thesis work chose Ge/Si ART (aspect ratio trapping) substrates as the Si platform to overcome the material mismatch between AlGaAs/GaAs system and Si, and investigated the first and crucial step of successful VCSEL integration on Si platforms, which is the VCSEL distributed Bragg reflector (DBR) growth and characterization on Ge/Si ART substrates. Three types of samples were grown and characterized to reveal the quality of DBRs and ART substrates. The results show good quality and potential for high performance VCSEL. The ART-based DBRs have reflectance spectra comparable to those grown on conventional bulk GaAs substrates and have smooth morphology. High-resolution X-ray diffraction (HRXRD) rocking curves show that the residual stress and crystal quality of the Ge films depend on oxide trench patterns. Though GaAs-DBRs have sharper satellite peaks, ART-DBRs also show good structural quality, considering the effect of more complex substrate structure with SiO₂, Ge and strained-Ge. The main peaks’ full-width-at-half-maximum (FWHM) of ART-DBR are about twice as GaAs-DBR’s. Transmission electron microscopy (TEM) images reveal very good periodicity and uniformity that are unaffected by threading dislocations or residual strain. These results are very encouraging for the successful full VCSEL growth on these substrates and also confirm that virtual Ge substrates via the ART technique are effective Si platforms for optoelectronic integrated circuits.
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