JungHoon Shin

The characteristic carrier–Er interaction distance in Er-doped a-Si/SiO2 superlattices formed by ion sputtering

The characteristic interaction distance between Er3+ ions and carriers that excite them in Er-doped a-Si/SiO2 superlattices is investigated. Superlattice thin films consisting of 12 periods of a-Si/SiO2:Er/SiO2/SiO2:Er layers were deposited by ion sputtering and subsequent annealing at 950 °C. The dependence of the Er3+ photoluminescence intensity on the thickness of the Er-doped SiO2 layers is well-described by an exponentially decreasing Er-carrier interaction with a characteristic interaction distance of 0.5±0.1 nm.

Large-scale fabrication of single-phase Er2SiO5 nanocrystal aggregates using Si nanowires

Single-phase Er2SiO5 nanocrystal aggregates were produced on a large scale using Si nanowire (Si-NW) arrays as templates. A dense array of Si-NWs was grown by vapor-liquid-solid mechanism using Au catalyst on Si (111) substrate. Afterwards, ErCl3∙6H2O dissolved ethanol solution was spin coated and annealed first at 900°C for 4min in a flowing N2∕O2 environment and then at 1200°C in a flowing Ar environment for 3min. X-ray diffraction, scanning electron microscope, and high-resolution transmission electron microscope measurements indicate that due to the use of Si-NWs, such a short annealing procedure is sufficient to completely transform the Er-coated Si-NWs into a thick, large-area aggregate of pure, single-phase to Er2SiO5 oxyorthosilicate nanocrystals. The crystalline nature of Er2SiO5 film and the loose nature of the aggregate result in an atomlike Er3+ spectrum with a very narrow luminescence linewidth at 1.53μm, which together with a complete lack of temperature quenching of Er3+ luminescence and a ...

Birefringence and optical power confinement in horizontal multi-slot waveguides made of Si and SiO2

Through simulations and measurements, we show that in multi-slot thin film waveguides, the TM polarized modes can be confined mostly in the low refractive index layers of the waveguide. The structure consisted of alternating layers of a-Si and SiO(2), in the thickness range between 3 and 40 nm, for which the slots were the SiO(2) layers. Simulations were performed using the transfer matrix method and experiments using the m-line technique at 1.55 mum. The dependence of the birefringence and of the power confinement in the slots was studied as a function of the waveguide thickness, the Si and SiO(2) layer thicknesses, and the SiO(2) / Si layer thickness ratio. We find a large birefringence-a refractive index difference between TE and TM modes-as large as 0.8. For TM polarized modes, up to ~ 85% of the total power in the fundamental mode can be confined in the slots.

Performance analysis of nanocluster-Si sensitized Er-doped waveguide amplifier using top-pumped 470nm LED

We analyze the performance of nanocrystal-Si (nc-Si) sensitized Er-doped waveguide amplifier using coupled nc-Si-Erbium rate equation, and suggest novel structures / operation methods which can be used to enhance its performance figures. With 2-dimensional modified propagation equation applied for the pump / signal waves along with modest assumptions on design parameters, we show that 10dB of gain with 0dBm input signal can be achieved with currently available pump LED power.

Si nanocluster sensitization of Er-doped silica for optical amplet using top-pumping visible LEDs

A review is presented of Si nanocluster sensitization of Er-doped silica for planar optical amplifiers using top-pumping 470-nm light-emitting diodes (LEDs). The motivation and basic physical principles underlying the nanocluster sensitization are first reviewed. The material structures necessary for optimum performances are presented, with emphasis on the need for nanoscale engineering of the composition and structure. Evidence of optical gain using commercial GaN-visible LEDs are presented, and the simulation results of possible device performances described. Finally, some possible future directions for research are discussed

Enhancement of the green, visible Tb3+ luminescence from Tb-doped silicon-rich silicon oxide by C co-doping

The effect of C co-doping on the Tb3+ luminescence from Tb-doped silicon-rich silicon oxide (SRSO) films is investigated. Tb-doped SRSO films co-doped with C (SRSO:C) were deposited by electron cyclotron resonance plasma-enhanced chemical vapor deposition. The Tb3+ photoluminescence intensity is enhanced by the presence of nanocluster Si (nc-Si), and C co-doping further increases the Tb3+ photoluminescence intensity by more than an order of magnitude. The maximum enhancement is observed at the C content of ∼5 at. %, at which the Tb3+ luminescence is bright enough to be observed by the naked eye under ambient conditions. The 543 nm Tb3+ lifetimes were in the range of 0.5–1.2 ms, comparable to those from Tb-doped silica. Based on the results, we conclude that nanometer-sized nc-Si can excite Tb3+ ions via an Auger-type energy transfer, and that C co-doping greatly increases the efficiency of such exciton-mediated excitation of Tb3+.

Effects of silicon nanostructure evolution on Er3+ luminescence in silicon-rich silicon oxide/Er-doped silica multilayers

The effect of silicon nanostructure evolution on Er3+ luminescence is investigated by using multilayers of 2.5nm thin SiOx (x<2) and 10nm thin Er-doped silica (SiO2:Er). By separating excess Si and Er atoms into separate, nanometer-thin layers, the effect of silicon nanostructure evolution on np-Si sensitized Er3+ luminescence could be investigated while keeping the microscopic Er3+ environment the same. The authors find that while the presence of np-Si is necessary for efficient sensitization, the overall quality of np-Si layer has little effect on the Er3+ luminescence. On the other hand, intrusion of np-Si into Er-doped silica layers leads to deactivation of np-Si∕Er3+ interaction, suggesting that there is a limit to excess Si and Er contents that can be used.

Optical activation of Si nanowires using Er-doped sol-gel derived silica

Optical activation of Si nanowires (Si-NWs) using sol-gel derived Er-doped silica is investigated. Si-NWs of about 100 nm diameter were grown on Si substrates by the vapor–liquid–solid method using Au catalysts and H2 diluted SiCl4. Afterwards, Er-doped silica sol-gel solution was spin-coated, and annealed at 950 °C in flowing N2/O2 environment. Such Er-doped silica/Si-NWs nanocomposite is found to combine the advantages of crystalline Si and silica to simultaneously achieve both high carrier-mediated excitation efficiency and high Er3+ luminescence efficiency while at the same time providing high areal density of Er3+ and easy current injection, indicating the possibility of developing sol-gel activated Si-NWs as a material platform for Si-based photonics.

Range and stability of structural colors generated by Morpho-inspired color reflectors

The range and stability of structural colors generated by Morpho-inspired color reflectors are investigated. We find that despite the internal randomness of such structures that gives rise to their Morpho-like angle-independent iridescence, their colors under ambient lighting condition can be predicted by simple transfer-matrix calculations of corresponding planar multilayer structures. By calculating the possible range of colors generated by multilayers of different structures and material combinations using such transfer-matrix methods, we find that low-refractive index multilayers with intrastructure absorption, such as the melanin-containing chitin/air multilayer structure from the Morpho butterflies, can provide not only the most pure structural colors with the largest color gamut, but also the highest stability of color against variations in multilayer structure.

Design and Fabrication of Tb

We report on fabricating Tb-doped SiON microdisks on a Si chip for low-cost all-Si biosensor applications. The 120-nm-thin 10-μm diameter pedestal-type microdisks were designed and fabricated for optimum biosensing capabilities. Whispering gallery modes of fabricated microdisks were measured via UV top pumping and side-photoluminescence (PL) measurement, and Q-factors of several hundreds were obtained. Using the microdisk resonators to sense streptavidin using biotin functionalization is also demonstrated.