Ge-Photodetectors for Si-Based Optoelectronic Integration

High speed photodetectors are a key building block, which allow a large wavelength range of detection from 850 nm to telecommunication standards at optical fiber band passes of 1.3–1.55 μm. Such devices are key components in several applications such as local area networks, board to board, chip to chip and intrachip interconnects. Recent technological achievements in growth of high quality SiGe/Ge films on Si wafers have opened up the possibility of low cost Ge-based photodetectors for near infrared communication bands and high resolution spectral imaging with high quantum efficiencies. In this review article, the recent progress in the development and integration of Ge-photodetectors on Si-based photonics will be comprehensively reviewed, along with remaining technological issues to be overcome and future research trends

Localised tuneable composition single crystal silicon-germanium-on-insulator for low cost devices

The realisation of high quality silicon-germanium-on-insulator (SGOI) is a major goal for the field of silicon photonics because it has the potential to enable extremely low power active devices functioning at the communication wavelengths of 1.3 µm and 1.55 µm. In addition, SGOI has the potential to form faster electronic devices such as BiCMOS transistors, and could also form the backbone of a new silicon photonics platform that extends into the mid-IR wavelengths for applications in, amongst others, sensing and telecoms. In this paper, we present a novel method of forming single crystal, defect free SGOI using a rapid melt growth technique. We use tailored structures to form localised uniform composition SGOI strips, which are suitable for state of the art device fabrication. This technique could pave the way for the seamless integration of electronic and photonic devices using only a single, low cost Ge deposition step

On-Chip Nanoscale Plasmonic Optical Modulators

In this thesis work, techniques for downsizing Optical modulators to nanoscale for the purpose of utilization in on chip communication and sensing applications are explored. Nanoscale optical interconnects can solve the electronics speed limiting transmission lines, in addition to decrease the electronic chips heat dissipation. A major obstacle in the path of achieving this goal is to build optical modulators, which transforms data from the electrical form to the optical form, in a size comparable to the size of the electronics components, while also having low insertion loss, high extinction ratio and bandwidth. Also, lap-on-chip applications used for fast diagnostics, and which is based on photonic sensors and photonic circuitry, is in need for similar modulator specifications, while it loosens the spec on the modulator’s size. Silicon photonics is the most convenient photonics technology available for optical interconnects application, owing to its compatibility with the mature and cheap CMOS manufacturing process. Hence, building modulators which is exclusively compatible with this technology is a must, although, Plasmonics could be the right technology for downsizing the optical components, owing to its capability in squeezing light in subwavelength dimensions. Hence, our major goal is to build plasmonic modulators, that can be coupled directly to silicon waveguides. A Plasmonic Mach-Zehnder modulator was built, based on the orthogonal junction coupling technique. The footprint of the modulator is decreased to 0.6 4.7, extinction ratio of 15.8 dB and insertion loss of 3.38 dB at 10 volts was achieved in the 3D simulations. The voltage length product for the modulator is 47 V. The orthogonal junction coupler technique minimized the modulator’s footprint. On the other hand, photonic sensors favorably work in the mid-infrared region, owing to the presence of a lot of molecules absorption peaks in this region. Hence, III-V semiconductor media is used for this type of applications, owing to the availability of laser sources built of III-V media, and to the lower losses that these materials have in mid-infrared region. Hybrid plasmonic waveguide, formed of doped InAs, AlAs and GaAs is studied extensively. Based on this waveguide an electro-absorption modulator is built. The device showed an extinction ratio of 27 dB at 40 length, and 1.2 dB of insertion loss. The small device footprint predicts a much lower energy consumption

Fabrication and Characterization of Germanium Photodetectors

Ph.DDOCTOR OF PHILOSOPH

Towards monolithic integration of germanium light sources on silicon chips

Germanium (Ge) is a group-IV indirect band gap semiconductor, and therefore bulk Ge cannot emit light efficiently. However, the direct band gap energy is close to the indirect one, and significant engineering efforts are being made to convert Ge into an efficient gain material monolithically integrated on a Si chip. In this article, we will review the engineering challenges of developing Ge light sources fabricated using nano-fabrication technologies compatible with Complementary Metal-Oxide-Semiconductor (CMOS) processes. In particular, we review recent progress in applying high-tensile strain to Ge to reduce the direct band gap. Another important technique is doping Ge with donor impurities to fill the indirect band gap valleys in the conduction band. Realization of carrier confinement structures and suitable optical cavities will be discussed. Finally, we will discuss possible applications of Ge light sources in potential photonics-electronics convergent systems