UBC Theses and Dissertations
Impact of doping on epitaxial Ge thin film quality and Si-Ge interdiffusion Guangnan, Zhou
Germanium-on-silicon (Ge-on-Si) structure-based semiconductor devices are playing an increasingly important role in large-scale dense photonic integration, especially in silicon (Si) photonics. Si photonics has emerged as an effective solution to overcome the wiring limit imposed on integrated circuits with continued scaling by using optical interconnects instead metal interconnects. A Si-compatible laser is the last missing piece in optical interconnects on Si platforms. Recently, III-V lasers on Ge/Si substrates and Ge-on-Si lasers were demonstrated as the most promising candidates, in which Ge layers function as either the transition layers or the optical gain layers. For different applications, the requirements on Ge film quality and Ge/Si interface interdiffusion are different. Si-Ge interdiffusion during high-temperature growth or fabrication steps changes the distribution of Ge and increases atomic intermixing, which degrades device performance. However, studies on the doping impact on Ge film quality and Si-Ge interdiffusion are very limited, which were addressed in this work. We investigate Ge-on-Si film quality systematically under different types of doping conditions (phosphorus, arsenic and boron) for the first time. It’s found that the boron doping significantly impairs the Ge film quality, while arsenic and phosphorus can effectively reduce the threading dislocation density without the commonly used defect annealing. This provides a new method to fabricate high-quality Ge-on-Si films, which can avoid undesired Si-Ge interdiffusion. Si-Ge interdiffusion with different doping at Ge/Si interfaces has been investigated experimentally and theoretically. The enhancement of interdiffusion was observed in n-type (phosphorus and arsenic) doped Ge-on-Si. The phenomenon is attributed to the Fermi-level effect. A quantitative model of Si-Ge interdiffusion under high n-type doping was proposed. The model agrees well with the experimental data. This is also the first study on the quantitative modeling of Si-Ge interdiffusion with high n-type doping across the full Ge range. This work is of technical significance for the structure, doping and process design of Ge-on-Si structure-based devices including the two laser types mentioned above, Ge modulators and Ge photodetectors.
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