Semiconductor Membrane Research Articles

Scalable wafer-to-fiber transfer method for lab-on-fiber sensing

We present an efficient and flexible method to realize micro- and nano-optical structures on the tip of optical fibers. We demonstrate this approach for a fiber-tip sensor consisting of a photonic crystal (PhC) structure in a semiconductor membrane on the cleaved facet of a telecom fiber. The PhC structure is fabricated on a wafer by lithography and etching and then transferred to the fiber facet by a simple mechanical pickup process through an opening in the substrate, without the need for adhesives or a micromanipulator. Due to its reliability, scalability, and the use of wafer-scale fabrication methods, this process increases the possibilities for fiber-tip applications at the industrial level. With the fabricated fiber tip sensors, we demonstrate sensing of the refractive index and temperature, with resonance wavelength shifts of 120 nm/RIU and 95 pm/K, respectively.

Ultrasonic Inspection and Self-Healing of Ge and 3C-SiC Semiconductor Membranes

Knowledge of the mechanical properties and stability of thin film structures is important for device operation. Potential failures related to crack initiation and growth must be identified early, to enable healing through e.g. annealing. Here, three square suspended membranes, formed from a thin layer of cubic silicon carbide (3C-SiC) or germanium (Ge) on a silicon substrate, were characterised by their response to ultrasonic excitation. The resonant frequencies and mode shapes were measured during thermal cycling over a temperature range of 20–100 °C. The influence of temperature on the stress was explored by comparison with predictions from a model of thermal expansion of the combined membrane and substrate. For an ideal, non-cracked sample the stress and Q-factor behaved as predicted. In contrast, for a 3C-SiC and a Ge membrane that had undergone vibration and thermal cycling to simulate extended use, measurements of the stress and Q-factor showed the presence of damage, with the 3C-SiC membrane subsequently breaking. However, the damaged Ge sample showed an improvement to the resonant behaviour on subsequent heating. Scanning electron microscopy showed that this was due to a self-healing of sub-micrometer cracks, caused by expansion of the germanium layer to form bridges over the cracked regions, with the effect also observable in the ultrasonic inspection. [2020-0017]

Fabrication of Hybrid Membranes Containing Nylon-11 and Organic Semiconductor Particles with Potential Applications in Molecular Electronics.

Chemical degradation is a major disadvantage in the development of organic semiconductors. This work proposes the manufacture and characterization of organic semiconductor membranes in order to prevent semiconductor properties decreasing. Semiconductor membranes consisting of Nylon-11 and particles of π-conjugated molecular semiconductors were manufactured by high-vacuum evaporation followed by thermal relaxation. Initially, and with the aim of obtaining semiconductor particles, bulk heterojunction (BHJ) was carried out using green chemistry techniques between the zinc phthalocyanine (ZnPc) and the zinc hexadecafluoro-phthalocyanine (F16ZnPc) as n-type molecular semiconductors with the p-type molecular semiconductor dibenzotetrathiafulvalene (DBTTF). Consequently, the π-conjugated semiconductors particles were embedded in a Nylon-11 matrix and characterized, both structurally and considering their optical and electrical properties. Thin films of these materials were manufactured in order to comparatively study the membranes and precursor semiconductor particles. The membranes presented bandgap (Eg) values that were lower than those obtained in the films, which is an indicator of an improvement in their semiconductor capacity. Finally, the membranes were subjected to accelerated lighting conditions, to determine the stability of the polymer and the operating capacity of the membrane. After fatigue conditions, the electrical behavior of the proposed semiconductor membranes remained practically unaltered; therefore, they could have potential applications in molecular electronics. The chemical stability of membranes, which did not degrade in their polymer compound, nor in the semiconductor, was monitored by IR spectroscopy.

Ti-doped indium gallium oxide electrolyte–insulator–semiconductor membranes for multiple ions and solutes detectors

Detecting multiple ions and solutes in human body is important to medical examinations of patients. In this study, Ti-doped InGaO (IGO) electrolyte–insulator–semiconductor (EIS) biosensors were fabricated for multiple ion and solute sensing capability. To optimize the sensing performance, rapid thermal annealing could enhance up to 70% hydrogen ion sensitivity and more than 50% multiple ion and solute sensitivity compared with the as-deposited sample owing to improvement of material quality. Ti-doped IGO EIS multianalyte biosensors show promise for future portable biosensing applications.

A frequency-tunable nanomembrane mechanical oscillator with embedded quantum dots

Hybrid systems consisting of a quantum emitter coupled to a mechanical oscillator are receiving increasing attention for fundamental science and potential applications in quantum technologies. In contrast to most of the presented works in this field, in which the oscillator eigenfrequencies are irreversibly determined by the fabrication process, we present here a simple approach to obtain frequency-tunable mechanical resonators based on suspended nanomembranes. The method relies on a micromachined piezoelectric actuator, which we use both to drive resonant oscillations of a suspended Ga(Al)As membrane with embedded quantum dots and to fine-tune their mechanical eigenfrequencies. Specifically, we excite oscillations with frequencies of at least 60 MHz by applying an AC voltage to the actuator and tune the eigenfrequencies by at least 25 times their linewidth by continuously varying the elastic stress state in the membranes through a DC voltage. The light emitted by optically excited quantum dots is used as a sensitive local strain gauge to monitor the oscillation frequency and amplitude. We expect that our method has the potential to be applicable to other optomechanical systems based on dielectric and semiconductor membranes possibly operating in the quantum regime.

Construction of ternary Ag@ZnO/TiO2 fibrous membranes with hierarchical nanostructures and mechanical flexibility for water purification

Rational design of semiconductor membrane photocatalyst with good mechanical flexibility and excellent photocatalytic activity is of significance for environmental remediation. Herein, flexible Ag@ZnO/TiO2 fibrous membranes with hierarchical nanostructures were fabricated through combining a simple electrospinning method and subsequent hydrothermal reaction and photodeposition process. In the ternary nanocomposite, ZnO nanorods were firmly anchored onto TiO2 nanofibers, while Ag nanoparticles were evenly decorated on the surface of both ZnO and TiO2. Benefiting from the improved light absorption, large surface area, and effective charge separation, the resultant Ag@ZnO/TiO2 membranes displayed superior photocatalytic degradation efficiency of 91.6% toward tetracycline hydrochloride within 1 h, and also exhibited prominent antibacterial activity with a 6.5 log inactivation of E. coli after 1 h simulated solar light exposure. Significantly, the membrane photocatalyst still preserved structural integrity and mechanical flexibility after utilization. This study provides an alternative approach for designing and synthesizing flexible TiO2-based membrane photocatalysts toward high-efficiency water purification.

Comparison of single-side and double-side pumping of membrane external-cavity surface-emitting lasers.

We studied and compared single-side pumping (SSP) and double-side pumping (DSP) of a semiconductor membrane external-cavity surface-emitting laser (MECSEL). The MECSEL-active region was based on an AlGaAs quantum well structure embedded between two silicon carbide (SiC) wafer pieces that were used as transparent intra-cavity (IC) heat spreaders creating a symmetrical cooling environment. The gain structure targeted emission at 780 nm, a wavelength region that is important for many applications, and where the development of high-brightness high-power laser sources is gaining more momentum. By DSP at 20°C heat sink temperature, we could reduce the laser threshold from 0.79 to 0.69 W of absorbed pump power, while the maximum output power was increased from 3.13 to 3.22 W. The differential efficiency was improved from 31.9% to 34.4%, which represents a record value for SiC-cooled vertically emitting semiconductor lasers. The improvements are enabled by a reduced thermal resistance of the gain element by 9% compared to SSP. The beam quality was measured to be M2<1.09. Finally, we demonstrate a maximum tuning range from 767 to 811 nm. This wavelength range was not addressed by any MECSEL or vertical external-cavity surface-emitting laser device before and extends the available wavelengths for semiconductor based high-quality beam and high-power laser sources to a wavelength window relevant for quantum technology, spectroscopy, or medicine.

In-place bonded semiconductor membranes as compliant substrates for III-V compound devices.

Overcoming the critical thickness limit in pseudomorphic growth of lattice mismatched heterostructures is a fundamental challenge in heteroepitaxy. On-demand transfer of light-emitting structures to arbitrary host substrates is an important technological method for optoelectronic and photonic device implementation. The use of freestanding membranes as compliant substrates is a promising approach to address both issues. In this work, the feasibility of using released GaAs/InGaAs/GaAs membranes as virtual substrates to thin films of InGaAs alloys is investigated as a function of the indium content in the films. Growth of flat epitaxial films is demonstrated with critical thickness beyond typical values observed for growth on bulk substrates. Optically active structures are also grown on these membranes with a strong photoluminescence signal and a clear red shift for an InAlGaAs/InGaAs/InAlGaAs quantum well. The red shift is ascribed to strain reduction in the quantum well due to the use of a completely relaxed membrane as the substrate. Our results demonstrate that such membranes constitute a virtual substrate that allows further heterostructure strain engineering, which is not possible when using other post-growth methods.

Erythrocyte fouling on micro-engineered membranes.

Crossflow microfiltration of plasma from blood through microsieves in a microchannel is potentially useful in many biomedical applications, including clinically as a wearable water removal device under development by the authors. We report experiments that correlate filtration rates, transmembrane pressures (TMP) and shear rates during filtration through a microscopically high channel bounded by a low intrinsic resistance photolithographically-produced porous semiconductor membrane. These experiments allowed observation of erythrocyte behavior at the filtering surface and showed how their unique deformability properties dominated filtration resistance. At low filtration rates (corresponding to low TMP), they rolled along the filter surface, but at higher filtration rates (corresponding to higher TMP), they anchored themselves to the filter membrane, forming a self-assembled, incomplete monolayer. The incompleteness of the layer was an essential feature of the monolayer's ability to support sustainable filtration. Maximum steady-state filtration flux was a function of wall shear rate, as predicted by conventional crossflow filtration theory, but, contrary to theories based on convective diffusion, showed weak dependence of filtration on erythrocyte concentration. Post-filtration scanning electron micrographs revealed significant capture and deformation of erythrocytes in all filter pores in the range 0.25 to 2 μm diameter. We report filtration rates through these filters and describe a largely unrecognized mechanism that allows stable filtration in the presence of substantial cell layers.

New Development of Membrane Base Optoelectronic Devices.

It is known that one factor that affects the operation of optoelectronic devices is the effective protection of the semiconductor materials against environmental conditions. The permeation of atmospheric oxygen and water molecules into the device structure induces degradation of the electrodes and the semiconductor. As a result, in this communication we report the fabrication of semiconductor membranes consisting of Magnesium Phthalocyanine-allene (MgPc-allene) particles dispersed in Nylon 11 films. These membranes combine polymer properties with organic semiconductors properties and also provide a barrier effect for the atmospheric gas molecules. They were prepared by high vacuum evaporation and followed by thermal relaxation technique. For the characterization of the obtained membranes, Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were used to determine the chemical and microstructural properties. UV-ViS, null ellipsometry, and visible photoluminescence (PL) at room temperature were used to characterize the optoelectronic properties. These results were compared with those obtained for the organic semiconductors: MgPc-allene thin films. Additionally, semiconductor membranes devices have been prepared, and a study of the device electronic transport properties was conducted by measuring electrical current density-voltage (J-V) characteristics by four point probes with different wavelengths. The resistance properties against different environmental molecules are enhanced, maintaining their semiconductor functionality that makes them candidates for optoelectronic applications.

Multi-harmonic quantum dot optomechanics in fused LiNbO3–(Al)GaAs hybrids

We fabricated an acousto-optic semiconductor hybrid device for strong optomechanical coupling of individual quantum emitters and a surface acoustic wave. Our device comprises of a surface acoustic wave chip made from highly piezoelectric LiNbO3 and a GaAs-based semiconductor membrane with an embedded layer of quantum dots. Employing multi-harmonic transducers, we generated sound waves on LiNbO3 over a wide range of radio frequencies. We monitored their coupling to and propagation across the semiconductor membrane, both in the electrical and optical domain. We demonstrate the enhanced optomechanical tuning of the embedded quantum dots with increasing frequencies. This effect was verified by finite element modelling of our device geometry and attributed to an increased localization of the acoustic field within the semiconductor membrane. For moderately high acoustic frequencies, our simulations predict strong optomechanical coupling, making our hybrid device ideally suited for applications in semiconductor based quantum acoustics.

3D Scaffolds: Deterministic Integration of Biological and Soft Materials onto 3D Microscale Cellular Frameworks (Adv. Biosys. 9/2017)

In article number 1700068, John A. Rogers, Ralph G. Nuzzo, and co-workers present direct ink write (DIW)-assisted integration of soft and cellular materials onto compressively buckled microframeworks that are constructed using polymer or high performance silicon semiconductor membranes. These scaffolds provide unique 3D environments upon which to study cellular migration and hydrogel integration. The cover was designed by Joselle M. McCracken.

Comparison of different bonding techniques for efficient strain transfer using piezoelectric actuators.

In this paper, strain transfer efficiencies from a single crystalline piezoelectric lead magnesium niobate-lead titanate substrate to a GaAs semiconductor membrane bonded on top are investigated using state-of-the-art x-ray diffraction (XRD) techniques and finite-element-method (FEM) simulations. Two different bonding techniques are studied, namely, gold-thermo-compression and polymer-based SU8 bonding. Our results show a much higher strain-transfer for the “soft” SU8 bonding in comparison to the “hard” bonding via gold-thermo-compression. A comparison between the XRD results and FEM simulations allows us to explain this unexpected result with the presence of complex interface structures between the different layers.

Nanoscale Layer Transfer by Hydrogen Ion-Cut Processing: A Brief Review Through Recent U.S. Patents.

A hydrogen-based Ion-Cut layer-transfer technique, the so-called Ion-Cut or Smart-Cut processing, has been used in transferring a semiconductor membrane onto a desired substrate to reveal unique characteristics on a nanoscale size and to build functional electronic and photonic devices that are used for specific purposes. For example, the sub-100 nm thick silicon membrane transferred onto an insulator became a key substrate for fabricating nanoscale integrated circuit (IC) devices. Recent U.S. patents have exhibited integration of various thinning approaches requiring precision of a few nanometers in fabricating large-area semiconductor nanomembranes, especially for silicon. This paper reviews published patents and work on fabricating sub-100 nm silicon membranes with welldefined features without a chemical-mechanical polishing (CMP) thinning process. This included material analysis leads to ultraprecision thickness in the sub-100 nm region. This paper combines an analysis of peer-reviewed articles and issued patents using focused review keywords of hydrogen implantation, wafer bonding, and layer splitting. The quality of selected patents was appraised based on the authors' 20-year research experience in the field of ultrathin silicon layer-transfer technology. The paper covered more than 10 U.S. patents that have been filed on hydrogen-based Ion-Cut layer-transfer techniques. These patents described approaches for inserting hydrogen ions to split at a well-defined location and then transfer the as-split silicon membrane at the nanoscale thickness onto a desired substrate. Hydrogen-trap sites, implantation energy, and interface of the distinct doped regions could define the layer-split location. The insertion of high-dose hydrogen ions could be thoroughly achieved by ion implantation, plasma ion immersion implantation (PIII), plasma diffusion, and electrolysis. The article concludes with the discussion of the patent-orientated review of layer-transfer techniques and makes some concrete suggestions for manufacturing the FDSOI substrate, the key material technology to fabricate nanoscale microelectronics for applications in artificial intelligence for "Industry 4.0."

Recent advances in free-standing single crystalline wide band-gap semiconductors and their applications: GaN, SiC, ZnO, β-Ga2O3, and diamond

Free-standing single crystalline semiconductor membranes have gained intensive attention over the last few years due to their versatile usage in many applications.

Semiconductor membrane external-cavity surface-emitting laser (MECSEL)

Optically pumped semiconductor disk lasers are an important class of solid state lasers. Despite all their advantages, however, they suffer from heat incorporation into the active region caused by the excess energy of the pump photons. To overcome the limits of common methods in thermal management, we realized a semiconductor membrane external-cavity surface-emitting laser (MECSEL) consisting of a diamond heat spreader sandwiched active region design without a monolithically integrated distributed Bragg reflector (DBR). This diamond-sandwich approach improves the heat dissipation out of the active region and makes generally low-heat conductive DBRs obsolete. In an AlGaInP-based system, we demonstrate 595 mW output power at a wavelength of 657 nm and heatsink temperature of 10°C. The MECSEL enables a variety of new material combinations for new laser wavelengths and further potential for power scaling.

Transparency of graphene and other direct-gap two-dimensional materials

Graphene and other two-dimensional materials display remarkable optical properties, including a simple light transparency of $T \approx 1 - \pi \alpha$ for light in the visible region. Most theoretical rationalizations of this "universal" opacity employ a model coupling light to the electron's crystal momentum and put emphasis on the linear dispersion of the graphene bands. However, such a formulation of interband absorption is not allowable within band structure theory, because it conflates the crystal momentum label with the canonical momentum operator. We show that the physical origin of the optical behavior of graphene can be explained within a straightforward picture with the correct use of canonical momentum coupling. Its essence lies in the two-dimensional character of the density of states rather than in the precise dispersion relation, and therefore the discussion is applicable to other systems such as semiconductor membranes. At higher energies the calculation predicts a peak corresponding to a van Hove singularity as well as a specific asymmetry in the absorption spectrum of graphene, in agreement with previous results.

Energy Cost Analysis of Membrane Distributed-Reflector Lasers for On-Chip Optical Interconnects

The power consumption of lateral-current-injection semiconductor membrane distributed-reflector lasers with a λ/4 shift region has been theoretically evaluated, in terms of their ultralow-power-consumption and high-speed modulation operations. This paper contains an investigation into the optimal structure of the membrane laser in terms of its energy cost, for use in on-chip optical interconnections. The total power consumption was evaluated, taking Joule heating into account by assuming the device resistance. It was found that the large Joule heating effect present in shorter cavities limits a reduction of their power consumption. As a result, an energy cost of 63 fJ/bit can be obtained for 10 Gb/s data transmission, while maintaining the necessary power output required for a cavity length of 12 μm. We have provided a guide for designing microcavity lasers in terms of their Joule heating power.

Temperature measurement and phonon number statistics of a nanoelectromechanical resonator

Measuring thermodynamic quantities can be easy or not, depending on the system that is being studied. For a macroscopic object, measuring temperatures can be as simple as measuring how much a column of mercury rises when in contact with the object. At the small scale of quantum electromechanical systems, such simple methods are not available and invariably detection processes disturb the system state. Here we propose a method for measuring the temperature on a suspended semiconductor membrane clamped at both ends. In this method, the membrane is mediating a capacitive coupling between two transmission line resonators (TLR). The first TLR has a strong dispersion, that is, its decaying rate is larger than its drive, and its role is to pump in a pulsed way the interaction between the membrane and the second TLR. By averaging the pulsed measurements of the quadrature of the second TLR we show how the temperature of the membrane can be determined. Moreover the statistical description of the state of the membrane, which is directly accessed in this approach is significantly improved by the addition of a Josephson junction coupled to the second TLR.

Low-threshold-current operation of membrane distributed-feedback laser with surface grating bonded on Si substrate

A lateral-current-injection (LCI) membrane distributed-feedback (DFB) laser with a surface grating structure (incorporating a slight step) emitting in the 1550 nm wavelength range was fabricated on a Si substrate by the adhesive bonding of benzocyclobutene. For a semiconductor membrane thickness of 158 nm and a surface grating depth of 30 nm, a threshold current of as low as 390 µA, with a corresponding threshold current density of 540 A/cm2, was obtained for a cavity length of 360 µm and a stripe width of 0.2 µm under a room-temperature continuous-wave (RT-CW) condition.