In this Letter, we report an approach to experimentally determine the optomechanical coupling coefficient of coupled cavities, taking advantage of the ultra-fine cavity positioning capability of a nanoelectromechanical system (NEMS) actuator design. The approach is simple and flexible and can measure the optomechanical coupling coefficient as a function of the coupled cavities' slot gap. In addition, the ratio of mechanical detunings of the odd and even resonance modes can make the existing approach to the decoupling of thermo-optic and optomechanical effects more precise and applicable to more types of cavities.

In this paper, we demonstrate a novel split-ladder photonic crystal cavity, which can be tuned across a very large wavelength range by an on-chip integrated nano-electromechanical actuator. The nano-electromechanical actuator is used to control the cavity's central gap. When the cavity gap is widened, the resonance wavelength is blue-shifted correspondingly. The dimensions of the proposed split-ladder cavity are designed by 3D Finite-difference time-domain (FDTD) calculations. We fabricated and tested the devices. Experimental results show that the optomechanical coupling coefficient of the second order resonance mode is about 80 GHz/nm. In addition, there is a relatively linear relationship between the resonance shift and the gap change. The maximum measured resonance wavelength shift is about 17 nm, corresponding to a cavity central gap increase of 26 nm.

In this Letter, we report an approach to controlling the bistability of double-coupled photonic crystal cavities with a nanoelectromechanical comb drive, in which the optical force and thermo-optic effect form a feedback mechanism to the effective index of the cavities, and the gap width between the cavities is steered by the comb drive. A model based on temporal coupled mode theory is established to analyze this approach. Hysteresis loops characterizing the bistability are experimentally achieved by sweeping the gap width forward and in reverse. In addition, the experiments also demonstrate that the bistability is tunable by varying the input light power.

Nanoscale all-optical circuits driven by optical forces have broad applications in future communication, computation, and sensing systems. Because human society faces huge challenges of energy saving and emission reduction, it is very important to develop energy-efficient nano-optomechanical devices. Due to their high quality (Q) factors, resonance modes of cavities are capable of generating much larger forces than waveguide modes. Here we experimentally demonstrate the use of resonance modes of double-coupled one-dimensional photonic crystal cavities to generate bipolar optical forces. Attractive and repulsive forces of -6.2 nN and 1.9 nN were obtained with respective launching powers of 0.81 mW and 0.87 mW in the waveguide just before cavities. Supported by flexible nanosprings (spring constant 0.166 N/m), one cavity is pulled to (pushed away from) the other cavity by 37.1 nm (11.4 nm). The shifts of the selected resonance modes of the device are mechanically and thermally calibrated with an integrated nanoelectromechanical system actuator and a temperature-controlled testing platform respectively. Based on these experimentally-obtained relations, probe mode shifts due to the optomechanical effect are decoupled from those due to the thermo-optic effect. Actuated by the third-order even pump mode, the optomechanical shift of the second-order even probe mode is found to be about 2.5 times its thermal shift, indicating a highly efficient conversion of light energy to mechanical energy.

We demonstrate tuning of double-coupled one-dimensional photonic crystal cavities by their out-of-plane nanomechanical deformations. The coupled cavities are pulled by the vertical electrostatic force generated by the potential difference between the device layer and the handle layer in a silicon-on-insulator chip, and the induced deformations are analyzed by the finite element method. Applied with a voltage of 12 V, the cavities obtain a redshift of 0.0405 nm (twice the linewidth) for their second-order odd resonance mode and a blueshift of 0.0635 nm (three times the linewidth) for their second-order even resonance mode, which are mainly attributed to out-of-plane relative displacement. Out-of-plane tuning of coupled cavities does not need actuators and corresponding circuits; thus the device is succinct and compact. This working principle can be potentially applied in chip-level optoelectronic devices, such as sensors, switches, routers, and tunable filters.

A wide-range split-ladder photonic crystal cavity which is tuned by changing its intrinsic gap width is designed and experimentally verified. Different from the coupled cavities that feature resonance splitting into symmetric and anti-symmetric modes, the single split-ladder cavity has only the symmetric modes of fundamental resonance and second-order resonance in its band gap. Finite-difference time-domain simulations demonstrate that bipolar resonance tuning (red shift and blue shift respectively) can be achieved by shrinking and expanding the cavity's gap, and that there is a linear relationship between the resonance shifts and changes in gap width. Simulations also show that the split-ladder cavity can possess a high Q-factor when the total number of air holes in the cavity is increased. Experimentally, comb drive actuator is used to control the extent of the cavity's gap and the variation of its displacements with applied voltage is calibrated with a scanning electron microscope. The measured wavelength of the second-order resonance shifts linearly towards blue with increase in gap width. The maximum blue shift is 17 nm, corresponding to a cavity gap increase of 26 nm with no obvious degradation of Q-factor.

We report bonding and diffusion behavior of nitrogen incorporated into InSb wafer by two-step implantation. Three nitrogen-containing regions, i.e., a surface accumulation region, a uniform region, and a tail region, were observed in the samples after post annealing. X-ray photoelectron spectroscopy measurements at different depths reveal that majority of the nitrogen forms In-N bonds in the uniform region but exists as interstitial defects in the tail region. The diffusion coefficients of nitrogen in InSb were obtained by fitting the modified Fick’s law with experimental data and the activation energy of 0.55 ± 0.04 eV extracted confirms the interstitial dominating diffusion of nitrogen in the InSb wafer.

Because of the gradient distribution of arsenic through the thickness of an InP layer, stress gradient in the structural layer of an InP-based Fabry-Perot (FP) cavity structure could be introduced during the fabrication process. This stress gradient, usually tensile at the upper surface and compressive at the lower surface, could induce a significant out-of-plane deformation, which may eventually affect its optical performance. White-light vertical scanning interferometry is employed to measure the stress-induced deflection of InP-based cantilever and membrane components used in a FP cavity structure. Deformation patterns caused by stress gradient in various cantilever and membrane structures with different configurations and geometries are investigated through experiments and simulations. The results indicate that the stress gradient induced during the fabrication process results in varying degrees of the FP structural deformation, which is further influenced by the configurations and geometries of the structural membranes and supporting beams. Four types of membrane structures of a FP cavity device are studied, and the results are compared to that obtained using a finite element analysis. (C) 2010 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3421968]

In the present study, we have investigated the incorporation of 2DEG AlxGa1-xN/GaN heterostructures with different Al content (19% and 39%) in UV metal-semiconductor-metal photodetectors (PDs), employing Schottky contacts. The structural properties of the heterostructures on sapphire substrates have been characterized by transmission electron microscopy, high resolution X-ray diffraction, atomic force microscopy, and UV micro-Raman spectroscopy. In order to study the behaviors of the interface phonon modes observed from such 2DEG structures, UV Raman measurements were simultaneously performed with and without applied bias voltages. The electrical properties of the UV PDs have been correlated to the optical observations. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3447813] All rights reserved.

InSbN p-n junctions prepared by N+ and Mg+ implantation into InSb wafers for long wavelength infrared photodetection are demonstrated for the first time. The detection wavelength can be controlled by monitoring the implanted nitrogen. The measured peak wavelengths are consistent with the bandgaps of the alloys calculated using a 10-band k·p model based on In-N bond.

The formation of highly activated ultrashallow junctions is one of the main challenges for the forthcoming generation of complementary metal oxide semiconductor (CMOS) devices. Co-implantation of impurities such as carbon (C) or fluorine (F) is an attractive technique. However, junction optimization can only be achieved with a complete understanding of the underlying physical mechanisms. In this paper, the effect of C/F co-implant on boron (B)-doped preamorphized silicon during the soak annealing is extensively studied. C/F atoms are located in the middle range between the B/BF2 concentration profiles and the end-of-range (EOR) defect band, with the aim of reducing the interactions of dopants with the interstitials released from EOR region. Isochronal annealing study is performed to investigate the impact of C/F codoping on the dopant de/reactivation behavior. It is shown that transient enhanced diffusion can be reduced by both co-implant schemes. The B-doped junction formed with the C co-implant is relatively stable and dopant deactivation is inhibited, while it is presumed that F atoms form B-F complexes, which reduces the B activation level. A physical insight on the dopant-defect interactions associated with C/F co-implant is established through the combination of diffusion and activation studies during soak annealing. c 2007 The Electrochemical Society.

Recent advances in high-speed networks have made micro-electro-mechanical systems (MEMS) find some niche applications in tunable optical devices. Indium phosphide (InP)-based MEMS have an inherent advantage of being direct band gap as compared to silicon and can thus be used in MEMS structures with light emission/detection capability. In this paper, we report an in-depth study using nanoindentation to determine the mechanical properties of InP free-standing structures that could be incorporated in optical MEMS. The fabrication process for InP-based cantilever beams and membranes is also reported. Young's modulus of the material is determined from both loading and unloading of the InP cantilever beam through a bending test. We also discuss the deformation behaviour of the InP cantilever beam. Indentation on an InP substrate was conducted using a spherical indenter of known radius, in addition to the conventional Berkovich tip. The results were compared with ideal analytical methods. Experiments were also carried out to determine Young's modulus and hardness using continuous stiffness mode (CSM) tests. In addition, as a benchmark, experiments on silicon and sapphire substrates are also discussed. The results show good agreement in the mechanical properties obtained through different experiments.

Using a combination of selective dry etching techniques, surface micro-machined GaN and ZnO micromechanical structures are demonstrated on silicon-on-insulator (SOI) substrates. The dry releasing technique employs a controlled gas phase pulse etching with non-plasma xenon difluoride (XeF2), which selectively etches the Si overlayer of SOI, thus under-cutting the wide bandgap semiconductor material on top. This method prevents crystal damage of overhanging wide bandgap semiconductor mechanical structures. The mechanical properties of these released microstructures are characterized by micro-Raman spectroscopy.

We present a method for the design and fabrication of InP-based free-standing microelectromechanical systems structures, which include microcantilever beams and Fabry–Perot membranes. The membrane is designed to satisfy both mechanical and optical requirements for a wavelength division multiplexing device and micro-Raman spectroscopy technique is used to evaluate surface stresses. The membrane profile is measured using a white-light interferometry technique, and the effect of the structure geometry on residual stress formation is discussed. From the results obtained, we propose a novel filter design that shows minimum surface profile deviation and stresses.

We report growth of InGaN/GaN multi-quantum-wells (MQWs) structures and GaN layers on silicon-on-insulator (SOI) substrates by metalorganic chemical vapor deposition (MOCVD). The growth conditions were tuned to realize blue-green emission peaks centered around 420-495 nm from such MQWs on SOI. X-ray diffraction, atomic force microscopy, scanning electron microscopy, and photoluminescence techniques were used to characterize the MQWs. Using a combination of selective dry etching techniques, GaN micromechanical structures are demonstrated on silicon-on-insulator (SOI) substrates. The dry releasing technique employs a controlled gas phase pulse etching with non-plasma xenon difluoride (XeF2), which selectively etches the Si overlayer of SOI, thus undercutting the GaN material on top. The mechanical properties of these released microstructures are characterized by micro-Raman spectroscopy. Such approach to realize multi-color light-emitting InGaN/GaN MQW structures and GaN micromechanical structures on SOI substrates is suitable for the integration of InGaN/GaN-based optoelectronic structures on SOI-based micro-opto-electromechanical systems (MOEMS) and sensors.

A novel InP-based microactuator, which is actuated by electrostatic means, has been proposed, designed, fabricated, and characterized for tuning applications in the 1.5 μm wavelength domains. Its structural design is based on the global optimization method. The tunable device is a big square membrane, which is supported by four identical cantilever beams. The three alternating layers Si3N4/SiO2 as a distributed Bragg reflector (DBR) mirror, which were previously reported, have been formed on the top of the membrane. Based on the optical interferometric measurements, the proposed Fabry–Perot filter has demonstrated a maximum deflection of ∼321 nm with an applied voltage up to 12 V, an average sensitivity of ∼27 nm/V, a pull-in voltage of 12.7 V, and a release voltage of 10.7 V. It is also observed that its natural frequency is 88.4 kHz. This measured frequency implies that the tuning speed of our device is fast for optical operations within 0.01 ms. In addition, our device’s mirror remains so flat with a good planarity of 0.07°, which is strictly required for the filter’s optical performance. This optical performance can be achieved, when the micromachined structure has a tuning displacement up to ∼38 nm with a low tuning voltage up to 5 V. When compared with the finite element models (FEM), which were generated by the commercialized software, Coventor™, our experimental results agree well in terms of the natural frequency, pull-in voltage and deflections. Thus, our tunable filter, which is based on the optimized design, enables better performances including reduced actuation voltages, large pull-in voltage, improved device reliability, and fast switching times. Our device can also quickly snap back to the original position. In addition, the undesired spring-softening effect has been reduced.

The continual downscaling of silicon devices for integrated circuits requires the formation of pn junctions that are progressively shallower, incorporate increasing levels of electrically active dopant, and sustain minimal implantation damage. In the case of boron implanted into preamorphized Si, the authors show that all these goals can be accomplished simultaneously through the use of an atomically clean surface, which during annealing acts as a large sink that removes Si interstitials selectively over dopant interstitials.

We are able to fabricate both polycrystalline and amorphous indium zinc oxide thin films. All the thin films exhibited an n-type semiconductor behavior with room-temperature conductivities in the range of 2.5×103–1.58×103 (Ωcm)−1. A nanoscaled conductivity inhomogeneity was observed in polycrystalline films by means of conducting atomic force microscopy, with morphology effect excluded by simultaneous topographic mapping. This effect has been explained in the presence of highly conducting In2O3 and Zn2In2O5 nano crystalline phases imbedded in amorphous matrix. On the other hand, excellent electrical homogeneity throughout the amorphous film was observed, suggesting its promising potential in microelectronic device applications.

Wafer bonding or wafer fusion is a method of combining two same or dissimilar materials, either atomically or by means of adhesive. In this paper we report a new process to bond thin film Indium Phosphide (InP) to oxidized Silicon (100) substrates at low temperatures (>250°C). The treatment of InP epitaxial structures to oxygen plasma and the Si substrate to chemical treatment aids the substrates in contact bonding at room temperature. A thermal treatment at 220°C, completes the wafer fusion, with uniform bonding occurring along the length and breadth of the sample. The InP substrate is removed, resulting in a thin film of two micron InP bonded to oxidized Si. The InP thin film was studied for its structural and optical quality by high-resolution scanning electron microscopy, micro-PL and micro-Raman. The thin-film exhibited excellent quality and was patterned and released to form cantilever structures, showing the process capability of integrating free-standing III-V thin-films on Si platform.