We investigate theoretically the infrared optical response characteristics of metallic armchair/zigzag-edge graphene nanoribbons (A/ZGNRs) to an external longitudinally polarized electromagnetic field at low temperatures. Within the framework of linear response theory at the perturbation regime, we examine the optical infrared absorption threshold energy, absorption power, dielectric function, and electron energy loss spectra near the neutrality points of the systems. It is demonstrated that, by some numerical examples, the photon-assisted direct interband absorptions for AGNR exist with different selection rules from those for ZGNR and single-walled carbon nanotube at infrared regime. This infrared optical property dependence of GNRs on field frequency may be used to design graphene-based nanoscale optoelectronic devices for the detection of infrared electromagnetic irradiations.

An InGaAsP-InP transistor laser (TL) at 1.55 microm has been designed and modeled. The proposed TL has a deep-ridge waveguide structure with the multiple quantum wells (MQWs) buried in the base-emitter junction, which provides good optical and electrical confinement and can effectively reduce the optical absorption and lateral leakage current. Good laser performance has been predicted by numerical modeling based on which the epitaxial growth was carried out by metalorganic chemical vapor deposition (MOCVD). The effect of p-dopant (Zn) diffusion on the QW performance was investigated by a re-growth procedure. By introducing a graded p-doping profile, the Zn diffusion into the MQWs was effectively controlled. With an average doping density of 1 x 10(18) cm(-3) in the base contact layer, the InGaAsP MQWs demonstrated high PL intensity at 1.51 microm and clear satellite diffraction peaks in the XRD spectrum.

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 shortreach optical interconnects, excellent performance has been achieved so far on waveguides, modulators and detectors, which use Si compatible materials (e.g. SiO 2 , Si 3 N 4 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 SiO 2 , Ge and strained-Ge. The main peaks' full-widthat-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

A 1550 InGaAsP-InP multiple-quantum-well (MQW) transistor laser is numerically modeled. The proposed structure has a deep-ridge waveguide and asymmetric doping profile in the base (i.e. only the part below QWs of the base is doped) which provides good optical and electrical confinement and effectively reduces the lateral leakage current and optical absorption. The important physical models and parameters are discussed and validated by modeling a conventional ridge-waveguide laser diode and comparing the results with the experiment. The simulation results of the transistor laser demonstrate a low threshold (< 10 mA) and a > 25 % slope efficiency with the current gain of 2 ∼ 4. The optical saturation and voltage-controlled operation are also demonstrated.

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