Theoretical Investigation On InAs/GaAs Quantum Dot Semiconductor Optical Amplifier And Quantum Dot Fabrication

Semiconductor optical amplifier (SOA) has been widely used in optical amplification and all optical signal processing for next generation optical network, and its improvement is of great importance. The characteristics of SOA is in nature controlled in its active region by the intra- or interband carrier dynamics, which is eventually determined by the energy band structure of the active area. Comparing with bulk and quantum well structure, quantum dot has confinements of carriers in three dimensions which endows it with atomic-like discrete states. This gives quantum dot SOA a serious of advantages over traditional SOAs. In this work, several research achievements and contributions are summarized both theoretically and experimentally.In theory, firstly, single-band approximation of k.p perturbation method with strain included is carried out to calculate the band structure of InAs/GaAs cylindrical quantum dot. Specific energy states in quantum dot of different sizes are analyzed. Two main carrier scattering mechanisms: longitudinal optical phonon scattering and Auger scattering in quantum dot are then investigated. Ultra-fast carrier dynamics are analyzed in different carrier densities and temperatures, which provides guidance for quantum dot SOA optimizations. Second, a two-electrode quantum dot SOA is proposed, and its gain and phase recovery processes are investigated utilizing detailed quantum dot SOA numerical model. Carrier recovery mechanisms in different bias configurations are discussed. Thirdly, a multi-section circuit model of quantum dot SOA with improved convergency and simulation efficiency is established by employing PSPICE electric circuit simulator. Then various characteristics of quantum dot SOA are simulated using this circuit model. Cascaded with optical filter and electro-absorption modulator, the equivalent circuit model of quantum dot SOA is also applied for optical wavelength conversion.In experiment, InAs/GaAs self-assembled quantum dot epitaxy by metal organic chemical vapor deposition is investigated, and influence of growth parameters such as temperature, growth time andⅤ/Ⅲratio on quantum dot morphology are analyzed with corresponding physical explanations presented. Finally, effects of InGaAs strain reducing layer on quantum dot morphology and luminescence characteristics are studied, which is benificial for the further improvements of quantum dot qualities.