The paper presents the effect of ICP-RIE etching time using one-component plasma on various parameters of an InAs/GaSb type II superlattice matrix. In the studies, two samples used at different BCl3 gas flow rates were compared and it was found that using a lower flow rate of 7 sccm results in obtaining a smoother sidewall morphology. Next, five periodic mesa-shaped structures were etched under identical conditions, but using a different time. The results indicated that the ICP-RIE method using a BCl3 flow rate of 7 sccm, ICP:RIE power ratio of 300W:270W allowed the ICP:RIE formation of a periodic mesa-shaped structure with smooth and perpendicular sidewalls.

This work reports on the impact of defects on the parameters of type II InAs/GaSb superlattices (SLs) and photoconductors (PCs) from the very long wavelength infrared region. SLs were grown by means of molecular beam epitaxy and characterised using microscopes, high-resolution X-ray diffractometry (HRXRD) and low-temperature photoluminescence (LT-PL). PCs were investigated using Fourier-transform infrared spectroscopy and a current-voltage measurements. The basic technological parameters were optimised using 30-period SLs. Tests on the growth temperature showed that different defect types dominated in SL samples of different thicknesses. The diffuse scattering in reciprocal space maps (RSMs) taken for 200-period SLs was the mirror image of that for 30-period SLs. Scanning electron microscope (SEM) images of 200 period SLs revealed three types of defects: holes, slits and others not belonging to the first two groups. Slits were the predominant type. The diameter of the defects determined by SEM and HRXRD was about 2.5 mu m. The cross section along the defects was made using focus-ion beam technique. The investigations using high-resolution transmission electron mi-croscopy revealed the origins of the defects: holes were formed at the SL/buffer interface and propagated throughout entire SL, while slits were created in the volume of the SL without disturbing the surrounding crystal lattice. The lowest defect density was found for an SL grown at 425 degrees C. The highest overall crystal quality, measured using an HRXRD rocking curve, was obtained for an SL deposited at 405 degrees C, while the highest optical quality was determined for an SL at 445 degrees C by means of LT-PL. The best parameters were achieved for PCs grown at two lower temperatures. The difference in the effective bandgaps of the PCs made it difficult to determine the optimal value of the growth temperature. The effective bandgap for three PCs was determined based on the spectral dependences of the photoresponse measured at 20 K. Activation energies for high (150-300 K) and low (<50 K) temperature ranges were estimated from R(1000/T) dependence.

In this paper, the study of defects in InAs/GaSb type-II superlattices using high-resolution an x-ray diffraction method as well as scanning (SEM) and transmission (TEM) electron microscopy is presented. The investigated superlattices had 200 (#SL200), 300 (#SL300), and 400 (#SL400) periods and were grown using molecular beam epitaxy. The growth conditions differed only in growth temperature, which was 370 °C for #SL400 and #SL200, and 390 °C for #SL300. A wings-like diffuse scattering was observed in reciprocal space maps of symmetrical (004) GaSb reflection. The micrometer-sized defect conglomerates comprised of stacking faults, and linear dislocations were revealed by the analysis of diffuse scattering intensity in combination with SEM and TEM imaging. The following defect-related parameters were obtained: (1) integrated diffuse scattering intensity of 0.1480 for #SL400, 0.1208 for #SL300, and 0.0882 for #SL200; (2) defect size: (2.5–3) μm × (2.5–3) μm –#SL400 and #SL200, (3.2–3.4) μm × (3.7–3.9) μm –#SL300; (3) defect diameter: ~1.84 μm –#SL400, ~2.45 μm –#SL300 and ~2.01 μm –#SL200; (4) defect density: 1.42 × 106 cm−2 –#SL400, 1.01 × 106 cm−2 –#SL300, 0.51 × 106 cm−2 –#SL200; (5) diameter of stacking faults: 0.14 μm and 0.13 μm for #SL400 and #SL200, 0.30 μm for #SL300.

Indium-based micro-bump arrays, among other things, are used for the bonding of infrared photodetectors and focal plane arrays. In this paper, several aspects of the fabrication technology of micrometer-sized indium bumps with a smooth surface morphology were investigated. The thermal evaporation of indium has been optimized to achieve ~8 μm-thick layers with a small surface roughness of Ra = 11 nm, indicating a high packing density of atoms. This ensures bump uniformity across the sample, as well as prevents oxidation inside the In columns prior to the reflow. A series of experiments to optimize indium bump fabrication technology, including a shear test of single columns, is described. A reliable, repeatable, simple, and quick approach was developed with the pre-etching of indium columns in a 10% HCl solution preceded by annealing at 120 °C in N2.

In the present study, SACX0307-ZnO and SACX0307-TiO 2 nano-composite solder pastes were fabricated. The ceramic reinforcements were used in 1wt% and with different primary particle sizes between 50-200nm. The soldering properties and microstructure of the solder joints were investigated. The nano-particles were mixed into the solder paste by standard ball milling process. Reflow soldering technology has been applied to prepare solder joints and spreading tests from the different solder alloys. The solder joints were evaluated by shear test, and cross-sections were prepared to investigate the metallographic properties by Scanning Electron Microscopy (SEM). The different ceramic nano-particles had different effects on the solderability of solder alloys. Best results were observed in the case of TiO2 nano-particles with improved wetting and mechanical strength. The microstructural investigations showed considerable grain refinement and the modified grain boundary/interfacial properties, which could cause the increase of the mechanical parameters.

In the paper, the results of the study on how etching type influences the quality of mesa structures in discrete antimonide-based photodetectors are presented. Devices based on both symmetrical and asymmetrical InAs/GaSb type-II superlattices (T2SLs) designed for mid- (MWIR) and long-wavelength infrared spectral range, respectively were tested. Mesa structures were formed using photolithography followed by wet or inductively coupled plasma – reactive ion etching. The former was based on H3PO4:C4H6O6:H2O:H2O2 solution, and dry etching was performed in BCl3:Ar plasma. The quality of mesas was evaluated using a scanning electron microscope. The current-voltage characteristics of MWIR photodetectors based on the symmetric T2SL show significantly lower leakage currents for plasma etched devices.

We report the first experimental parametric analysis of subwavelength monolithic high-contrast grating (MHCG) mirrors. To date, subwavelength grating mirrors have been fabricated by suspending a thin grating membrane in the air or placing it on a low refractive index material - a scheme that requires sophisticated processing and makes the gratings sensitive to mechanical stress, impeding current injection, and heat dissipation if used in active devices. Inherently MHCGs are well suited for optoelectronic devices because they can be fabricated in all possible material systems. Here we demonstrate above 90% optical power reflectance, strong polarization discrimination. Based on experimental analysis aided by numerical simulations, we demonstrate the possibility of tuning the spectral characteristics of MHCGs reflectance for more than 200 nm via modification of the duty cycle of the MHCG stripes. We show our MHCG tuning method is convenient to define the properties of MHCG devices during the device processing.

The results of the study on threading dislocation density (TDD) in homo- and heteroepitaxial GaSb-based structures (metamorphic layers, material grown by applying interfacial misfit array (IMF) and complex structures) deposited using molecular beam epitaxy are presented. Three measurement techniques were considered: high-resolution x-ray diffraction (HRXRD), etch pit density (EPD), and counting tapers on images obtained using atomic force microscopy (AFM). Additionally, high-resolution transmission electron microscopy (HRTEM) was used for selected samples. The density of dislocations determined using these methods varied, e.g., for IMF-GaSb/GaAs sample, were 6.5 × 108 cm−2, 2.2 × 106 cm−2, and 4.1 × 107 cm−2 obtained using the HRXRD, EPD, and AFM techniques, respectively. Thus, the value of TDD should be provided together with information about the measurement method. Nevertheless, the absolute value of TDD is not as essential as the credibility of the technique used for optimizing material growth. By testing material groups with known parameters, we established which techniques can be used for examining the dislocation density in GaSb-based structures.

Fabrication of approx. 3 THz Al0.15Ga0.85As/GaAs QCLs grown by Molecular Beam Epitaxy equipped with Ta/Cu or Ti/Cu waveguide claddings will be presented. Our previous studies showed that copper layers as the waveguide claddings are most promising in THz QCLs technology. The theoretical predictions showed that lasers with Ti/Cu or Ta/Cu claddings (where Ti and Ta play the role of diffusion barriers and improve adhesion) show the smallest waveguide losses when compared with other metals. The main important issue of the presentation will be the wafer bonding of the QCL active region and GaAs receptor wafer. We will compare the results of ex-situ and in-situ bonding technology. The structures were tested by optical microscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDXS). Our studies show that it was necessary to apply at least 5 nm-thick diffusion-barrier layers, as well as to keep all of the process temperatures below 400C in order to ensure the barrier tightness. The next important issue was control of composition of metallic claddings, in order to provide the control of the refractive index profiles of the claddings. The ridge structure lasers were fabricated with ridge width in the range 100 – 140 µm, formed by dry plasma etching in BCl3/Cl2/Ar mixture in ICP RIE system. The lasers operated with threshold current densities of approx. 1.2 kA/cm2 at 77 K and the Tmax = 130 K, when fed by 100-300 ns current pulses supplied with 0.3-1 kHz repetition frequencies.*This research is supported by The National Centre for Research and Development (bilateral cooperation, project no. 1/POLTUR-1/2016) and TUBITAK (Scientific and Technical Research Council of Turkey) project number 215E113.

In this paper, the relationship between the crystallographic structure of Cu-Sn intermetallic grains and Sn whisker growth was investigated. In order to prevent the influence of the elements in the alloy composition and the effect of the soldering process on the formation of the intermetallic layer, 99.99% pure Sn was vacuum evaporated onto Cu substrates. The Sn layer thickness was sub-micron region (similar to 400 nm in average) to reach considerable and rapid compressive stress on the tin layer originated by the intermetallic formation. The samples were stored at room temperature for 1 month. Different types of whiskers (nodule and filament) and the layer structure underneath were studied with a scanning ion microscopy and transmission electron microscopy. It was found that not only the thickness of the intermetallic layer and shape of the intermetallic grains affects the whisker growth but the crystallographic structure of the intermetallic grains as well. The susceptibility of the Sn layer to whisker development is higher in those regions where the intermetallic layer is composed of monocrystalline grains instead of those regions, where it is composed of polycrystalline grains. This effect can be explained by the higher compressive stress generated by the monocrystalline intermetallics compared to the polycrystalline ones. (C) 2019 Elsevier B.V. All rights reserved.

We report on the growth of fully relaxed and smooth GaSb layers with reduced density of threading dislocations, deposited on GaAs substrate. We prove that three parameters have to be controlled in order to obtain applicable GaSb buffers with atomically smooth surface: interfacial misfit (IMF), the etch pit density (EPD) and the growth mode. The GaSb/GaAs interfacial misfit array and reduced EPD <= 1.0 x 10(7) cm(-2) were easily obtained using As-flux reduction for 3 min and Sb-soaking surface for 10 s before the GaSb growth initiation. The successive growth of GaSb layer proceeded under the technological conditions described by the wide range of the following parameters: r(G) is an element of (1.5 divided by 1.9) angstrom/s, T-G is an element of (400 divided by 520)degrees C, V/III is an element of (2.3 divided by 3.5). Unfortunately, a spiral or 3D growth modes were observed for this material resulting in the surface roughness of 1.1 divided by 3.0 nm. Two-dimensional growth mode (layer by layer) can only be achieved under the strictly defined conditions. In our case, the best quality 1-mu m-thick GaSb buffer layer with atomically smooth surface was obtained for the following set of parameters: r(G) = 1.5 angstrom/s, T-G = 530 degrees C, V/III = 2.9. The layer was characterized by the strain relaxation over 99.6%, 90 degrees dislocations array with the average distance of 5.56 nm, EPD similar to 8.0 x 10(6) cm(-2) and 2D undulated terraces on the surface with roughness of about 1 ML. No mounds were observed. We belive that only thin and smooth GaSb layer with reduced EPD may be applied as the buffer layer in complex device heterostructures. Otherwise, it may cause the device parameters deterioration.

We report on the role of AlSb material in the reduction of threading dislocation density (TDD) in the GaSb/AlSb/GaAs system. The AlSb layers were grown using low-temperature (LT) MBE, exploiting the interfacial misfit (IMF) dislocation array. AlSb layers with four different thicknesses in the range of 1–30 nm were investigated. The results showed the inhibiting role of LT-AlSb layers in the reduction of TDD. Values of TDD as low as 2.2 × 106 and 6.3 × 106 cm−2 for samples with thin and thick AlSb layers were obtained, respectively. The filtering role of AlSb material was proven despite the IMF-AlSb/GaAs interface’s imperfectness caused by the disturbance of a 90° dislocation periodic array by, most likely, 60° dislocations. The dislocation lines confined to the region of AlSb material were visible in HRTEM images. The highest crystal quality and smoother surface of 1.0 μm GaSb material were obtained using 9 nm thick AlSb interlayer. Unexpectedly, the comparative analysis of the results obtained for the GaSb/LT-AlSb/GaAs heterostructure and our best results for the GaSb/GaAs system showed that the latter can achieve both higher crystal quality and lower dislocation density.

In this paper, we present the results of a theoretical and experimental investigation into the refractive index and absorption, at room temperature, of a 4 mu m-thick undoped epitaxial layer of GaSb deposited on a GaAs substrate. A theoretical formula for optical transmission through an etalon was derived, taking into account the finite coherence length of the light. This formula was used to analyse the measured transmission spectra. The refractive index was determined in a wide spectral range, between 0.105 eV and 0.715 eV. The absorption was determined for photon energies between 0.28 eV and 0.95 eV. An Urbach tail was observed in the absorption spectrum, as well as a constant increase in absorption in the spectral region above the band gap.

In the paper, the comparative analysis of type-II InAs/GaSb SLs deposited on three types of GaSb buffers: homoepitaxial, metamorphic and one grown using the interfacial misfit (IMF) array technique has been presented. The buffer layers as well as superlattices were grown under nominally identical technological conditions. HRXRD investigations proved better crystal quality of the metamorphic material than the IMF-GaSb. FWHMRC were equal to 156 arcsec and 196 arcsec, respectively. The surface roughness of about 1 ML and 4 MLs was obtained using the atomic force microscope for 4.0 mu m-metamorphic GaSb and 1.5 mu m-IMF-GaSb layers, respectively. The etch pits density for both buffers was similar, 1-2 x 10(7) cm(-2). Superlattice with 500 periods deposited on the homoepitaxial buffer was used as a reference of the best crystal quality. HRTEM images revealed straight InAs/GaSb interfaces with 1 ML thicknesses in this sample. The interfaces in SL deposited on IMF-GaSb buffer were undulated and smeared over 3 MLs. The use of the metamorphic buffer resulted in 1-2 ML straight InAs/GaSb interfaces. The main reason for this is the roughness of IMF-GaSb buffer with mounds on the surface. Based on the obtained results we have demonstrated the advantage of metamorphic approach over IMF growth mode in GaSb/GaAs material system. A two times thicker buffer could be the price worth paying for high quality structures, even when working in the production mode.

Low temperature co-fired ceramics (LTCC) materials are commonly used in many areas of microelectronics. Special application includes microwave devices packaging because of the possibility of dielectric constant controlling and the simplicity of the three-dimensional structure obtainment by multilayer lamination. The LTCC composites based on Al2O3 or cordierite ceramics with SiO2-Al2O3-B2O3-type glass co-fired with graphite addition are promising low dielectric constant materials. The presence of the introduced inner porosity, as well as not uniform microstructure of a glass-ceramic composite have a strong impact on its mechanical and electrical properties. The composite microstructure can be modified by graphite powder addition at the stage of preparation of slurries for tape casting. The graphite powder addition at the level of 25-50 wt% leads to the advantageous significant decrease of the dielectric constant although causes also detrimental lowering of mechanical strength of the composite, especially in the case of irregular pores distribution. This work was aimed at characterization of the microstructure, pore distribution and elemental composition for a series of the multilayer laminates containing dense external and porous internal layers with various degree of porosity formed as a result of burnout of graphite. The scanning electron microscopy study showed that both the degree of porosity irregularity and pores distribution and size depend on graphite content in the slurry. Mapping of the composition using energy dispersive spectroscopy method at the cross-section of the composite specimens allowed to observe distribution of the particular elements in the different regions of the multilayer composites.

A comprehensive investigation of the interfacial misfit (IMF) array formation has been carried out. The studies were based on the static phase diagram for GaAs (001) surface and As 2 dimers on the surface. Prior to the initiation of the GaSb growth two attempts of the temperature decreasing were performed: before and after the GaAs termination. The GaAs was grown in the optimal conditions for GaSb material. The influence of the interruption time on GaSb/GaAs heterostructure parameters was examined. Two cases were investigated: with and without Sb-soaking of the GaAs surface. The periodic array of edge dislocations at GaSb/GaAs interface was confirmed using Burger’s circuit theory. Careful examination of misfit surroundings revealed one uncompleted Burger’s vector that indicated one dislocation of mixed type among eight of the edge type. The distance between lattice sites of dislocations was 5.51 nm on average. The crystal quality of 5.0 µm GaSb layer was characterized by FWHM 2 θ / ω = 42 arcsec, FWHM RC = 125 arcsec. The EPD = 4 × 10 6 cm − 2 was estimated after etching in FeCl 3 :HCl solution. The Δ q z /Δ q x ratio of 0.60 for 5.0 µm GaSb layer was higher than for 2.5 µm GaSb layer of 0.59. The probable reason was the thickness-dependent 60° dislocation density. The electrical parameters measured for 2.5 µm GaSb were: p = 4.0 × 10 16 cm −3 (2.0 × 10 16 cm −3 ) and µ = 599 cm 2 /V s (3420 cm 2 /V s) at 300 K (77 K).

Different types of Sn coatings are widely used in the electronics industry. However, they are susceptible to spontaneous whisker formation which can cause reliability issues. In this paper, whisker growth from submicron Sn thin films was studied at room temperature for 150days. For this purpose, 99.99% pure Sn was vacuum evaporated onto 1.5mm thick Cu and ceramic substrates, with an average thickness of 400nm. It was found that the submicron thick Sn layers on a Cu substrate can generate intense whiskering directly after layer deposition. The microstructure, composition and grain orientation of the whiskers and the areas underneath were studied with a Scanning Ion Microscope (SIM) and a Transmission Electron Microscope (TEM). It was proven that the whisker growth was induced by Cu6Sn5 intermetallic layer growth between the Cu substrate and the Sn thin film which resulted in large stress within the film. We found the first evidence in a tin-copper layer system that the high stress due to the intermetallic formation itself can initiate the interfacial flow mechanism (without a direct mechanical load) between the Sn layer and the intermetallic layer. This phenomenon can explain the intense whisker growth from submicron Sn thin films.

Organic-inorganic hybrid system composed of bimetallic Au@Pt nanoparticles with diameter of a few nanometers uniformly dispersed in the conducting polymer matrix was synthesized by a simple electrochemical/chemical method on glassy carbon electrode. The elaborated catalyst demonstrates an enhanced specific catalytic activity (9.7 A mg(-1) Pt) in electrooxidation of formic acid. The reason of this improved performance is discussed in terms of the polymer structure used as the matrix for bimetallic catalyst and mechanism of formation of Au@Pt nanoparticles. Electrocatalytic activity of the hybrid systems obtained by means of two different procedures are compared to understand better the influence of the synthesis conditions on the properties of the catalyst. The composites are characterized by means HR-TEM, X-ray diffraction and X-ray fluorescence methods. Arrangement of nanoparticles in Au@ Pt composite is determined by EDX elemental mapping. A new method of preparation of the samples embedded in thin polymer film for XRD and XRF measurements is proposed. (C) 2017 Elsevier Ltd. All rights reserved.

Detailed microstructural studies were performed on Ni/Si ohmic contacts to silicon carbide in order to investigate the effect of initial Ni:Si ratio in as-deposited structures on the occurrence of characteristic defects in Ni silicide layers, such as voids, layer discontinuities, rough surface or rough interface. The chosen range of investigated Ni:Si ratios corresponded to delta-Ni2Si as a dominant phase after complete annealing sequence. Strong effect of the initial stoichiometry on the ohmic contact's microstructure was observed. The highest Ni concentration significantly lowered the temperature at which roughening of the surface and the interface occurred. The middle value of investigated concentrations resulted in the rough interface after high temperature annealing, while the lowest investigated Ni content preserved smooth interface but introduced large voids and layer discontinuities. After the first annealing step, gamma-Ni31Si12 and/or delta-Ni2Si phases were detected. In the ohmic contacts (after two-step annealing sequence), beside delta-Ni2Si, the metastable, high temperature phase theta-Ni2Si was detected (also referred to as Ni3Si2 center dot h). This phase can exist within a relatively broad range of Ni:Si stoichiometry. The stoichiometry change toward higher Si content, which occurs during high temperature annealing, was realized through this phase. Superstructures were detected in theta-Ni2Si (Ni3Si2 center dot h) and in-gamma-Ni31Si12 grains. The effect of the stoichiometry change on the morphology of the Ni silicide layers is discussed. (C) 2016 Elsevier B.V. All rights reserved.