Silicon Micro/Nano Light Emitters Based On Controllable Ge Quantum Dots

Optical transmission is a technology that using photon to transmit data. Due to the broad bandwidth and high data rate of optical transmission, electrical interconnect may be substituted by optical interconnect in the future. Silicon-based optical interconnect has been a great potential platform to realize interconnect on-chip due to the high operating speed, low power consumption, small footprint and compatibility with complementary metal-oxide semiconductor (CMOS) processes. There are four building blocks for silicon-based on-chip optical interconnects, including light sources, waveguides, modulators and detectors. Silicon(Si) is an indirect band gap semiconductor and is not an efficient light source due to the poor light emission efficiency. Germanium quantum dots (Ge QDs) are a promising light source due to the easy fabrication, the compatibility with silicon technology and ability of emitting light in the telecom-band.Single photons are very good as quantum bits. It is impossible to'eavesdrop' on a secure connection without being observed in the case of quantum key distribution. The miniaturization and integration of critical components in quantum information processing will result in a high speed secured communication system. Si photonic chips provide a highly integrated platform for quantum information communication and processing. To achieve the next generation integrated quantum information platform, the core issue is the realization of silicon-based quantum light sources. Single Ge QD is also a potential candidate for silicon-based quantum light source. This thesis will focus on the controllable fabrication of Ge QDs, the precice coupling between single Ge QD and photonic crystal nanocavity, the photoluminescence of cavity enhanced single Ge QD. The major research achievements are summarized as follows:(1) The growth process of GeSi material using molecular beam epitaxy is explored. Multilayer of high density Ge QDs are grown using "low temperature + high temperature" process, with a areal density of 9×109 cm-2. Large period nanohole patterns on Si substrate are fabricated via electron beam lithography and dry etching. We present a study on the growth of a low-density ordered Ge QD on a nanohole patterned Si (001) substrate by molecular beam epitaxy. Ordered Ge QDs with different periods are realized, the largest period being 15 ?m. We interpret the nucleation and growth mechanisms for the large period ordered QDs by calculating the surface chemical potential distribution via a kinetic model.(2) Two types of high resolution alignment markers used in electron beam lithography system are developed:the HfO2 makers and the deep etching markers on SOI substrate. Both two kind of alignment markers are compatible with high temperature process and have an alignment error of less than 25 nm. We demonstrate the feasibility of controllable coupling of a Ge single QD with a photonic crystal nanocavity on SOI substrate:the position of single QDs is predetermined by growing in an array of nanoholes that is aligned to a set of markers, allowing precise overlay between optical cavities and the single QDs array. The average misalignment between site-controlled Ge single QD and cavity center is about 22 nm.(3) The photoluminescence properties of cavity enhanced Ge single QD is investigated. Strong resonant luminescence from Ge single QD embedded in photonic crystal nanocavity is observed up to room temperature. The strongest resonant luminescence peak is obtained at 1498.8 nm, with an enhancement factor of over 1300. A Purcell factor ?60 is estimated from the photoluminescence enhancement, which is about much higher than the estimated Purcell factor of the L3 cavity with Ge QDs growth by traditional self-assembled epitaxy. We attribute the accurate spatial and spectral overlap between single QD and L3 cavity to be the main reason for the high Purcell enhancement. Four different kinds of transition processes are coexisting in Ge single QD, which consequently results in a broad band photoluminescence emission. The photoluminescence peak of MO mode and M3 mode are assigned to be light emission from QD ground state and excited state recombination, respectively. The activation energy of MO and M3 modes are fitted to be 151 and 83 meV, respectively.(4) Light emitters based on Ge QDs coupled with array of gold bowtie nanoantennas are fabricated and characterized on SOI substrate. Enhanced luminescence from Ge QDs is observed at room temperature with a maximum enhancement factor of 4.2 at 1577 nm. The light emission enhancement is due to the strong interaction between localized plasmonic mode of bowtie antennas and nearby Ge QDs. The average quantum efficiency enhancement for 240 nm bowtie antennas at 1577 nm is estimated to be 8.09 based on the data of PL enhancement factor, collection efficiency, and excitation rate.(5) The Ge-condensation technique is realized by the cyclic thermal oxidation and annealing of SiGe alloy. Ordered GeSi nanowires are fabricated using top-down technique and Ge condensation technique. The site and shape of GeSi nanowires is defined by electron beam lithography and dry etching; the size and Ge content of GeSi nanowires is mainly determined by Ge condensation process. Ordered GeSi nanowires with a ?10 nm cross-section and high Ge content (97%) were fabricated. As a demonstration of the application of ordered GeSi nanowires, we design and fabricated a series of photoconductive detectors based on GeSi nanowires.