A Time-Domain Perspective on the Structural and Electronic Response in Epitaxial Ferroelectric Thin Films on Silicon.

This operando study of epitaxial ferroelectric Pb(Zr0.48Ti0.52)O3 capacitors on silicon substrates studies their structural response via synchrotron-based time-resolved X-ray diffraction during hysteresis-loop measurements in the 2-200 kHz range. At high frequencies, the polarization hysteresis loop is rounded and the classical butterfly-like strain hysteresis acquires a flat dumbbell shape. We explain these observations from a time-domain perspective: The polarization and structural motion within the unit cell are coupled to the strain by the piezoelectric effect and limited by domain wall velocity. The solution of this coupled oscillator system is derived experimentally from the simultaneously measured electronic and structural data. The driving stress σFE(t) is calculated as the product of the measured voltage U(t) and polarization P(t). Unlike the electrical variables, σFE(t) and η(t) of the ferroelectric oscillate at twice the frequency of the applied electrical field. We model the measured frequency-dependent phase shift between η(t) and σFE(t).

Quantification of Crystalline Phases in Hf0.5Zr0.5O2 Thin Films through Complementary Infrared Spectroscopy and Ab Initio Supercell Simulations.

In the quest for thinner and more efficient ferroelectric devices, Hf0.5Zr0.5O2 (HZO) has emerged as a potential ultrathin and lead-free ferroelectric material. Indeed, when deposited on a TiN electrode, 1-25 nm thick HZO exhibits excellent ferroelectricity capability, allowing the prospective miniaturization of capacitors and transistor devices. To investigate the origin of ferroelectricity in HZO thin films, we conducted a far-infrared (FIR) spectroscopic study on 5 HZO films with thicknesses ranging from 10 to 52 nm, both within and out of the ferroelectric thickness range where ferroelectric properties are observed. Based on X-ray diffraction, these HZO films are estimated to contain various proportions of monoclinic (m-), tetragonal (t-), and polar orthorhombic (polar o-) phases, while only the 11, 17, and 21 nm thick are expected to include a higher amount of polar o-phase. We coupled the HZO infrared measurements with DFT simulations for these m-, t-, and polar o-crystallographic structures. The approach used was based on the supercell method, which combines all possible Hf/Zr mixed atomic sites in the solid solution. The excellent agreement between measured and simulated spectra allows assigning most bands and provides infrared signatures for the various HZO structures, including the polar orthorhombic form. Beyond pure assignment of bands, the DFT IR spectra averaging using a mix of different compositions (e.g., 70% polar o-phase +30% m-phase) of HZO DFT crystal phases allows quantification of the percentage of different structures inside the different HZO film thicknesses. Regarding the experimental data analysis, we used the spectroscopic data to perform a Kramers-Kronig constrained variational fit to extract the optical functions of the films using a Drude-Lorentz-based model. We found that the ferroelectric films could be described using a set of about 7 oscillators, which results in static dielectric constants in good agreement with theoretical values and previously reported ones for HfO2-doped ferroelectric films.

Dual-wavelength micro-resonator combining photonic crystal membrane and Fabry-Perot cavity.

We propose a novel system of dual-wavelength micro-cavity based on the coupling between a photonic crystal membrane (PCM); operating at the Γ- point of the Brillouin zone, with a Fabry-Perot vertical cavity (FP). The optical coupling, which can be adjusted by the overlap between both optical modes, leads to the generation of two hybrid modes separated by a frequency difference which can be tuned using micro-opto-electromechanical structures. The proposed dual-wavelength micro-cavity is attractive for application where dual-mode behaviour is desirable as dual-lasing, frequency conversion. An analytical model, numerical (FDTD) and transfer matrix method investigations are presented.

A simple perturbative analysis for fast design of an electrically pumped micro-disk laser.

A perturbative analysis is proposed to estimate optical losses for electrically pumped micro-disk lasers. The optical field interaction with the electrical contacts and the optimization of their implementation is investigated. Our model shows a good agreement with 3D Finite Difference Time Domain (FDTD) computation and can be used for designing contacts for thin micro-disks, with a considerably reduced calculation time. We also demonstrate that losses induced by the contacts can be exploited to select the optical mode of a micro-laser.

Surface emitting microlaser based on 2D photonic crystal rod lattices.

2D photonic crystal (2D PC) structures consisting in a square lattice of Indium Phosphide (InP) microrods bonded on a Silicon/Silica Bragg mirror are experimentally investigated. We focus on slow Bloch modes above the light line, especially at the Gamma-point where a vertical emission can be obtained. Stimulated emission around 1.5 microm is demonstrated in such structures, at room temperature, for the first time. In addition the achieved threshold power lies within the range reported for surface emitting devices based on conventional lattices of holes. It is shown that the laser mode is laterally confined by a carrier induced refractive index change, under pulsed excitation. It is also demonstrated that this type of 2D PC is well suited for sensors integrated in microfluidic systems.

Directional channel-drop filter based on a slow Bloch mode photonic crystal waveguide section.

A two-dimensional photonic crystal channel-drop filter is proposed. This device has two high group velocity waveguides that are selectively coupled by a single, low group velocity intermediate waveguide section. It exhibits computed quality factors as high as 1300, and directional dropping efficiencies as high as 90%.

Coupling analysis of heterogeneous integrated InP based photonic crystal triangular lattice band-edge lasers and silicon waveguides.

In recent years, many groups have envisioned the possibility of integrating optical and electronic devices in a single chip. In this paper, we study the integration of a photonic crystal laser fabricated in InP with a silicon passive waveguide. The coupling of energy between a 2D photonic crystal (PhC) triangular lattice band-edge laser and waveguide positioned underneath is analyzed in this paper. We show that a 40% coupling could be achieved provided the distance between the laser and the waveguide is carefully adjusted. A general description of the fabrication process used to realize these devices is also included in this paper.

Nanoparticles selectively immobilized onto large arrays of gold micro and nanostructures through surface chemical functionalizations.

Latex nanoparticles (100nm and 200nm diameter) were precisely located onto the gold regions of micro and nanopatterned gold/silica substrates through surface chemical functionalizations. The gold patterns were selectively functionalized with alkylthiols bearing biotin or amine headgroups. This selective functionalization allowed the trapping of streptavidin- or carboxy-functionalized latex nanoparticles onto the gold structures with very little non-specific adsorption onto the surrounding silica. Quantitative data of nanoparticle capture on gold and silica, obtained through SEM image analysis, showed a one to two order of magnitude increase on gold with a similar low coverage on silica (non-specific adsorption) thanks to chemical functionalizations. Single nanoparticles were captured at the gap of dimer gold nanostructures.

Analysis of hybrid photonic crystal vertical cavity surface emitting lasers.

Vertical resonators with a top mirror constituted of 1D photonic crystal membrane on top of a Bragg stack are investigated in this paper. These structures allow the fabrication of compact vertical-cavity surfaceemitting lasers, which can be designed, in addition, for in-plane emission. With this hybrid approach, fabrication problems related to both classical VCSEL and Photonic Crystal lasers may be significantly relaxed, given that a full Bragg stack is replaced by a single photonic crystal membrane and that the Photonic Crystal is not formed in the active gain layer.

Carrier-injection-based electro-optic modulator on silicon-on-insulator with a heterogeneously integrated III-V microdisk cavity.

A compact electro-optic modulator on silicon-on-insulator is presented. The structure consists of a III-V microdisk cavity heterogeneously integrated on a silicon-on-insulator wire waveguide. By modulating the loss of the active layer included in the cavity through carrier injection, the power of the transmitted light at the resonant wavelength is modulated; approximately 10 dB extinction ratio and 2.73 Gbps dynamic operation are demonstrated without using any special driving techniques.