Most dielectric materials have very weak electro-optic properties, whereas the optical properties of some plasmonic materials may be greatly tuned, especially around their plasma frequency, where dielectric constant is transiting between positive (“dielectric state”) and negative (“metallic state”) values. In this talk, we will review some of our recent work on electro-optical modulation and introduce a new concept, photonic MOS based on “optical property inversion”. This concept may provide inspiration for the development of nanophotonic devices. While the whole paper only discusses theory and modelling, some new experimental results will be presented in the on-site talk. Throughout this report, “static dielectric constant”, ɛ, refers to material dielectric constant in the DC or radio frequency (RF) regime; “optical dielectric constant”, ε, represents material dielectric constant in the near-infrared regime. This paper was re-written based on an Arxiv file [1].

By reducing the number of dimensions that light can propagate in from three down to two, one may gain control over the characteristics of propagation. This control can allow for “Stopped Light” (SL), where wavepackets of light are slowed down to a zero group velocity. This is achieved by designing planar metal-dielectric structures that are stacked in one dimension allowing for waveguide modes in the other two, and engineering the dispersion relation of these structures. Stopped light structures can be further optimized to reduce their dispersion and increase the number of spatial frequencies supported, which allows for confinement of electromagnetic energy over volumes smaller than the diffraction limit over fixed regions in space. If this electromagnetic energy is confined over a region that provides gain, the question arises, can amplification of this light energy occur? and indeed can a regime of lasing be entered into? We show that stopped light lasing is indeed possible, despite there being no resonant cavity in 2d to confine the light, and explore the properties of this new type of laser.

GaSb/GaAs and InSb/GaAs material systems can create type-II quantum nanostructures which provide interesting electronic and optical properties such as having long carrier life time, low carriers-recombination rate, and emitting/absorbing low photon energy. These characteristics of type-II nanostructures can be applied for infrared or gas detection devices, for memory devices and even for novel intermediate band solar cells. In contrast, lattice mismatches of GaSb/GaAs and InSb/GaAs material system are 7.8% and 14.6%, respectively, which need some specific molecular beam epitaxial (MBE) growth conditions for quantum nanostructure formation via Stranski–Krastanov growth mode.

In this paper, the growth of self-assembled GaSb and InSb quantum nanostructures on (001) GaAs substrate by using MBE was reported. The surface morphology of these two quantum nanostructures and their optical properties were characterized by atomic force microscopy and photoluminescence (PL). The experimental results were compared between these two quantum nanostructures. Due to the lattice mismatch in each material system and the difference in sticking coefficient of Ga- and In-atoms during epitaxial growth, we obtain GaSb/GaAs quantum dots (QDs) with a density ∼1010 dots/cm2 and InSb/GaAs QDs with a density of ∼108 dots/cm2. The facet analysis of individual quantum nanostructure in each material system reveals that GaSb/GaAs QD has a dome-like shape with nearly isotropic property while InSb QDs form a rectangular-like shape with elongation along [110]-direction showing a strong anisotropic property.

Low temperature PL spectra from capped GaSb and InSb quantum nanostructures show the energy peaks at 1.08-1.11 and 1.16-1.17 eV, respectively. The variations of PL peaks as a function of both temperature and excitation power are investigated. PL peak shows clear blue shift when excitation power is increased. This work manifests a possibility to use both GaSb and InSb quantum nanostructures for nanoelectronic and nanophotonic applications.

One main difference between practical device and ideal design for subwavelength grating structure is the tapered sidewall profile of grating, which is normally obtained by the practical CMOS-compatible fabrication and etching process. Our work has investigated the impacts of tapered sidewall profile on the subwavelength grating wideband reflector characteristics. Both zero-contrast gratings (ZCG) and high- contrast gratings (HCG) are numerically investigated in detail and the results show a distinct differences of the impacts of tapered sidewall profile of grating. The simulation results reveal that this factor play a critical role in determining the reflection bandwidth, average reflectance, and the band edge. Our study has potential in guiding the utilization of subwavelength grating wideband reflector on application of a variety of nanophotonic devices and their integration, as well as to facilitate the design of the fabrication process on the control of tapered sidewall profile.

CMOS-compatible fabrication and etching processes are often used in subwavelength grating structures manufacturing, it normally generates tapered sidewall profile of the gratings. In this work, we have studied the impacts on resonance mode characteristics of subwavelength grating structures due to the tapered sidewall profile, as well as grating with high aspect ratio. Our simulation results have revealed that both of these two factors play important roles on the resonance mode behavior of subwavelength grating devices. We also discussed the mechanism between the guided mode resonance and the grating cavity mode resonance. Our study will provide guidance for a series of integrated photonics devices applications, such as compact optical filter, photonics amplifier, and lasers, while the realistic subwavelength grating structure is considered.

The kinetics of Ge lateral overgrowth on SiO2 with line-shaped Si seeds is examined. The growth process is described by the difference between the growth rates of Ge on (100) planes (GR100) and <311> facets (GR311). The theoretical calculations well reproduce the growth kinetics. It is shown that narrowing the line-seeds helps Ge coalescence and flat film formation.

Here we fabricated and characterized a CMOS compatible metal-insulator-semiconductor (MIS) plasmonic tunnel junction for Si-based photonic circuitry. A grating structure was realized on MIS plasmonic tunnel junction via focused-ion-beam milling (FIB) to increase the intensity of the light emission that occurs during inelastic electron tunneling. Approximately 65 times higher intensity of light emission is achieved with the grating structure during the measurements.

Single crystals of Ln(NO3)3·Bpy2 where Ln = Eu, Gd, Nd, Tm, Er, La and Yb were fabricated and characterized. Materials have good optical quality, can be excited at UV or the rare earth ion transitions, demonstrate efficient luminescence and are suitable for thin film fabrication. Fabrication approaches and possible applications are discussed.

ZnMgTe(Cladding)/ZnTe(Core)/ZnMgTe(Cladding) thin film waveguide had been grown by molecular beam epitaxy (MBE) and presented a great potential to be a high performance Electro-optical (EO) modulator. For a low propagation loss ZnMgTe/ZnTe waveguide, thick cladding layer with high Mg composition (Mg %) is needed. However, the in-plane lattice mismatch of the fabricated device with high Mg % and thick cladding layer was large. It might cause the cladding/core interface roughness and asperities due to the misfit dislocation, and degrade the device performance. Because EO property of waveguide device is primarily influence by the structure thickness, the device efficiency improvement in this study was only considered to reduce the defects asperities that would cause propagation loss without decreasing the Mg % or the total thickness of the cladding layers. Therefore, we introduced a low Mg % layer between the cladding and the core layer to circumvent the effect of large lattice mismatch. The in-plane lattice mismatch of the devices was monitored using reciprocal space mapping, and surface morphologies were also observed using atom force microscope. The two-step index ZnMgTe/ZnTe waveguide had shown to have lower degree of relaxation compared to that of single-step index waveguide device with close Mg % and cladding layer thickness. Therefore, the crystal degradation of the two-step-index waveguide caused by lattice mismatch was successfully suppressed by introduction extra low Mg % layers. The morphologies of the two kinds of waveguide structures have similar surface asperities, which indicated the extra inserted layers did not produce additional large scale asperities at the interfaces that would increase the propagation loss.

The effects of GaAs anti-phase domains (APDs) on the growth of GaSb quantum dots (QDs) are investigated by molecular beam epitaxial growth of GaAs on Ge (001) substrate. Ge is a group-IV element and GaAs is a polar III-V compound semiconductor. Due to polar/non polar interface, GaAs APDs are formed. Initial formation of APD relates to a non-uniform growth of high index GaAs surfaces. However, due to high sticking coefficient of Sb atoms at low substrate growth temperature, GaSb QDs can be formed on the whole surface of the sample without any effects from APD boundary. The buffer layer growth temperature is one of the key roles to control the APDs formation. Therefore we tried to adjust the optimum conditions such as buffer layer thickness and growth temperature to get nearly flat sample surface with large APDs for high QDs density (∼ 8×109 dots/cm2). Low-temperature photoluminescence is conducted and GaSb QDs peak is observed at the energy range of 1.0 eV-1.3 eV.

In this work, we report a comparative investigation of InxGa1-xN (SL) and InxGa1-xN/GaN (MQW) structures with an indium content equivalent to x=10%. Both structures are grown on (0001) sapphire substrates using MOCVD and MBE growth techniques. Optical properties are evaluated for samples using PL characteristics. Critical differences between the resulting epitaxy are observed. Microstructures have been assessed in terms of crystalline quality, density of dislocations and surface morphology. We have focused our study towards the fabrication of vertical PIN photodiodes. The technological process has been optimized as a function of the material structure. From the optical and electrical characteristics, this study demonstrates the benefit of InGaN/GaN MQW grown by MOCVD in comparison with MBE for high speed optoelectronic applications.