InP Membrane Research Articles

Low-optical-loss, low-resistance Ag/Ge based ohmic contacts to n-type InP for membrane based waveguide devices

We present the development of Ag/Ge based ohmic contacts to n-type InP with both low contact resistances and relatively low optical losses. A specific contact resistance as low as 1.5×10−6 Ω cm2 is achieved by optimizing the Ge layer thickness and annealing conditions. The use of Ge instead of metal as the first deposited layer results in a low optical absorption loss in the telecommunication wavelength range. Compared to Au based contacts, the Ag based metallization also shows considerably reduced spiking effects after annealing. Contacts with different lengths are deposited on top of InP membrane waveguides to characterize the optical loss before and after annealing. A factor of 5 reduction of the propagation loss compared to the conventional Au/Ge/Ni contact is demonstrated. This allows for much more optimized designs for membrane photonic devices.

2D photonic-crystal optomechanical nanoresonator.

We present the optical optimization of an optomechanical device based on a suspended InP membrane patterned with a 2D near-wavelength grating (NWG) based on a 2D photonic-crystal geometry. We first identify by numerical simulation a set of geometrical parameters providing a reflectivity higher than 99.8% over a 50-nm span. We then study the limitations induced by the finite value of the optical waist and lateral size of the NWG pattern using different numerical approaches. The NWG grating, pierced in a suspended InP 265-nm thick membrane, is used to form a compact microcavity involving the suspended nanomembrane as an end mirror. The resulting cavity has a waist size smaller than 10μm and a finesse in the 200 range. It is used to probe the Brownian motion of the mechanical modes of the nanomembrane.

Vertical and Smooth Single-Step Reactive Ion Etching Process for InP Membrane Waveguides

In this paper we present a novel single-step RIE process for InP membrane optical waveguide etching. The optimization of the process is focused on the sidewall verticality and surface roughness of the etched profile. Significant improvement on the etched profile is achieved for the first time in a single-step RIE process. Loss measurement on fabricated membrane waveguides etched with the proposed RIE process results in a record low waveguide propagation loss (2.5 dB/cm).

Electrochemical growth of Co nanowires in ultra-high aspect ratio InP membranes: FFT-impedance spectroscopy of the growth process and magnetic properties.

The electrochemical growth of Co nanowires in ultra-high aspect ratio InP membranes has been investigated by fast Fourier transform-impedance spectroscopy (FFT-IS) in the frequency range from 75 Hz to 18.5 kHz. The impedance data could be fitted very well using an electric circuit equivalent model with a series resistance connected in series to a simple resistor-capacitor (RC) element and a Maxwell element. Based on the impedance data, the Co deposition in ultra-high aspect ratio InP membranes can be divided into two different Co deposition processes. The corresponding share of each process on the overall Co deposition can be determined directly from the transfer resistances of the two processes. The impedance data clearly show the beneficial impact of boric acid on the Co deposition and also indicate a diffusion limitation of boric acid in ultra-high aspect ratio InP membranes. The grown Co nanowires are polycrystalline with a very small grain size. They show a narrow hysteresis loop with a preferential orientation of the easy magnetization direction along the long nanowire axis due to the arising shape anisotropy of the Co nanowires.

Plasticity and Fracture of InP/Si Substructures

We report on the mechanical response of semiconductor substructures formed by InP membranes bonded to silicon. The bonded surfaces are of the order of ~ 1 cm2 and were bonded using oxide-free direct wafer bonding. Both the plastic response of the InP membrane and the InP/Si interface strength have been investigated using instrumented nanoindentation.

Fullerene-assisted electron-beam lithography for pattern improvement and loss reduction in InP membrane waveguide devices

In this Letter, we present a method to prepare a mixed electron-beam resist composed of a positive resist (ZEP520A) and C60 fullerene. The addition of C60 to the ZEP resist changes the material properties under electron beam exposure significantly. An improvement in the thermal resistance of the mixed material has been demonstrated by fabricating multimode interference couplers and coupling regions of microring resonators. The fabrication of distributed Bragg reflector structures has shown improvement in terms of pattern definition accuracy with respect to the same structures fabricated with normal ZEP resist. Straight InP membrane waveguides with different lengths have been fabricated using this mixed resist. A decrease of the propagation loss from 6.6 to 3.3 dB/cm has been demonstrated.

Instrumented nanoindentation and scanning electron transmission microscopy applied to the study of the adhesion of InP membranes heteroepitaxially bonded to Si

Instrumented nanoindentation and STEM have been combined ex situ to study the adhesion of 450 nm thick InP membranes to Si substrates. Three distinct regimes are identified in the deformation of the InP/Si stacks during these experiments: the first is plastic flow of InP at low loads; the second is elastic debonding of the InP membrane, far from the indented zone at medium loads; lastly, the local amorphisation of the underlying Si substrate at high loads. The regime of intermediate loads is shown to be particularly useful in the evaluation of the surface bonding energy of InP to Si.

A Nanorobotic System for In Situ Stiffness Measurements on Membranes

In order to characterize the mechanical behavior of fragile resonant microelectromechanical systems (MEMS)/nanoelectromechanical systems (NEMS), nondestructive measurements are required. In this paper, a cartography of local stiffness variations on a suspended micromembrane is established for the first time, by a tuning-fork-based dynamic force sensor inside a scanning electron microscope (SEM). Experiments are conducted individually on a batch of InP membranes 200 nm thin, using a 9-degree-of-freedom (dof) nanomanipulation system, complemented with virtual reality and automation tools. Results provide stiffness values in the range of a few newton per meter, with variations in a single sample depending on the membrane models.

Planar Concave Grating Demultiplexers on an InP-Membrane-on-Silicon Photonic Platform

We present measurement results of a 0.25 mm2 footprint eight-channel planar concave grating demultiplexer fabricated in a 300-nm-thick InP membrane adhesively bonded to silicon. The measured cross-talk between the different channels of the device is better than -18 dB, while the insertion loss is 2.8 dB. The power non-uniformity between the channels is 1.2 dB.

Evaluation of the surface bonding energy of an InP membrane bonded oxide-free to Si using instrumented nanoindentation

Instrumented nanoindentation is used in conjunction with scanning transmission electron microscopy to evaluate the mechanical resistance at the bonding interface of a 450 nm thick InP membrane bonded oxide-free to Si. Indentation using a Berkovich tip is shown to cause the planes in InP to rotate by as much as 16°. The shear stress resulting from this rotation causes the InP membrane to buckle, forming a debonded blister around the indented zone. The geometry of this blister is used to compute the surface bond energy of InP bonded oxide-free to Si. An average surface bonding energy of 585 mJ m−2 is reported.

Characterization of Three-Dimensional Single-Crystalline Porous InP Anodes for Li-Ion Batteries

This paper reports on the electrochemical and photo-(electro)chemical fabrication of a single-crystalline porous InP anode for Li-ion batteries. Additionally, a structural characterization by SEM and XRD as well as a battery characterization by cyclovoltammetry and battery cycling tests in half-cells are presented. This anode exhibits a high capacity per area (~63 mAh/cm2). It consists only of the active material (InP) and a thin Au layer as current collector. The maximum possible capacity of InP (~800 mAh/g) is achieved, which is much higher than the capacity of commercial graphite anodes (~350 mAh/g). The total anode capacity is freely scalable by adjusting the InP membrane thickness.

Ultra‐high aspect ratio Ni nanowires in single‐crystalline InP membranes as multiferroic composite

AbstractBy a combination of chemical etching, atomic layer deposition (ALD) and galvanic deposition it became possible to produce Ni nanowires (NWs) with ultra‐high aspect ratio (∼1000), embedded in a semi‐insulating, piezoelectric, single‐crystalline InP matrix. This Letter discusses the structural and magnetic properties of these Ni NWs. They are crystalline with a preferential growth direction of the grains in 〈111〉. For H ⊥ z, they show a very narrow hysteresis loop with a low coercivity (about 100 Oe) and a very low remanence squareness S of 0.08. So the combination of piezoelectric InP and magnetostrictive Ni forms a very promising multiferroic composite. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High-efficiency ultrasmall polarization converter in InP membrane

An ultrasmall (<10 μm length) polarization converter in InP membrane is fabricated and characterized. The device relies on the beating between the two eigenmodes of chemically etched triangular waveguides. Measurements show a very high polarization conversion efficiency of >99% with insertion losses of <-1.2 dB at a wavelength of 1.53 μm. Furthermore, our design is found to be broadband and tolerant to dimension variations.

Fabrication of a Single-Crystalline Porous InP Membrane by Electrochemical and Photoelectrochemical Etching

not Available.

Processing of photonic crystals in InP membranes by focused ion beam milling and plasma etching

We present a fabrication approach for photonic crystals and similar nanophotonic structures in InP using focused ion beam milling and plasma etching. The high quality of ion milling lithography in a dielectric hardmask is combined with reactive ion etching to obtain simultaneously fast processing speeds as well as smooth and vertical sidewalls. Different hardmask materials have been investigated yielding very good results for SiO 2 and Si x N y . Parameters for the optimization of lithography and plasma etching are given. Finally, results of a released InP membrane with a photonic crystal structure featuring elliptical base elements are presented.

Single-Crystalline Membranes in Indium Phosphide: Fabrication Process and Characterization Using FFT Impedance Analysis

This paper reports on the electrochemical and photo(electro)chemical fabrication of single-crystalline InP membranes with homogeneous surfaces allowing for adjustable pore shapes from roundish to square-like and various surface morphologies from extremely flat to cone-like pore wall tips. The InP membrane thickness is tunable from several tens of μm to almost 500 μm. FFT impedance data measured in-situ during pore etching can be easily fitted by an RC-component in series with a resistor and allow for precise in-situ prediction of the final membrane surface morphology and easy process parameter adjustment for the production of membranes with arbitrary membrane thicknesses.

Single-Crystalline Porous Indium Phosphide as Anode Material for Li-Ion Batteries

This paper reports on the electrochemical and photo-(electro)chemical fabrication of a single-crystalline porous InP anode, and its performance in Li-ion batteries. This anode exhibits high capacity per area (∼63 mAh/cm2). It consists only of the active material (InP) and a thin Au layer as a current collector. The maximum possible capacity of InP (∼800 mAh/g) is achieved, which is much higher than the capacity of commercial graphite anodes (∼350 mAh/g). The total anode capacity is freely scalable by adjusting the InP membrane thickness. The paper also shows the fabrication processes and a thorough battery characterization by cyclovoltammetry and battery cycling tests in half-cells.

Photonic integration in indium-phosphide membranes on silicon

A new photonic integration technique is presented, which enables the use of indium-phosphide-based membranes on top of silicon chips. This can provide the electronic chips (complementary metal-oxide semiconductor (CMOS)) with an added optical layer (indium-phosphide membrane on silicon (IMOS)) for resolving the communication bottleneck. Very small passive devices have been realised, with performances comparable to other membrane devices (propagation loss 7 dB/cm, negligible bending loss for micron size radii, 3 dB splitter with 0.6 dB excess loss, resonator with Q-factor of 15.500). Also, a new passive device is introduced, a 4.12 micron long polarisation converter which in simulations promises broadband performance and tolerant fabrication. Finally, an active/passive regrowth technique is investigated for submicron active regions within an otherwise mostly passive membrane. A good morphology is obtained around the interfaces between the active and passive regions. The processing involved did not damage the materials severely, so that light emission in micro-PL measurements was found. However, an increasing blue shift with decreasing size occurred, due to quantum well intermixing. Optimising the design and the processing can take care of this. Taken together, the results presented here show that it is feasible to realise extremely small passive and active devices in a photonic circuit in an InP membrane.

Ultra-low threshold polariton lasing in photonic crystal cavities

The authors show clear experimental evidence of lasing of exciton polaritons confined in L3 photonic crystal cavities. The samples are based on an InP membrane in air containing five InAsP quantum wells. Polariton lasing is observed with thresholds as low as 120 nW, below the Mott transition, while conventional photon lasing is observed for a pumping power one to three orders of magnitude higher.

Analogue modulation characteristics of InP membrane microdisc laser for in-building networks

Using thin membrane InP microdisc lasers heterogeneously integrated on a silicon on insulator (SOI) substrate having a broadband analogue modulation bandwidth of 11 GHz, analogue direct modulation with radio data signals (64 and 256 QAM, 20M symbols/s at 5 GHz RF carrier) is demonstrated. The demonstration shows the potential of the microdisc laser as a low-energy analogue optical transmitter with error-vector magnitude penalties of 3.6 and 4.2% for 64 and 256 QAM, respectively, and the low biasing currents for both DC (4 mW) and RF (0.1 mW) signals, which are compatible with signals and currents which can be supplied by a simple CMOS driving chip.