Thermoelectrically cooled focal plane arrays (FPAs) for the mid-wavelength infrared spectral range have been demonstrated. The mesa-shaped pixels were formed in pin InAs/GaSb heterostructure using dry etching. FPA with 320 x 256 resolution and a pixel pitch of 30 mu m was obtained. Indium die-bonding was applied to connect FPA and a read-out integrated circuit. The thermoelectrically cooled hybrid was hermetically sealed in a vacuum housing with a silicon window. The pictures of the hot soldering tip were detected using FPA at different temperatures.

This work reports on the investigation of homogeneity of the inside of indium micro -bumps/ columns placed on Ti/Pt/Au under bump metallisation. This is very important for connection resistivity, long-time durability, and subsequent hybridisation process (e.g., die -bonding). Gold reacts with indium to form intermetallic alloys with different chemo-physical parameters than pure indium. The geometrical and structural parameters of intermetallic alloys were analysed based on transmission electron microscope images. Distribution of elements in the investigated samples was determined using the transmission electron microscope with energy dispersive spectroscopy method. A thickness of intermetallic alloy was 1.02 mu m and 1.67 mu m in non -annealed (A) and annealed (B) indium columns, respectively. The layered and column -like interior structure of alloys was observed for both samples, respectively, with twice bigger grains in sample B. The graded chemical composition of Au -In intermetallic alloy was detected for the non -annealed In columns in contrast to the constant composition of 40% of Au and 60% of In for the annealed sample B. The atomic distribution has a minor impact on the In column mechanical stability. A yield above 99% of an In column with a 25 mu m diameter and a 11 mu m height is possible for a uniform columnar structure of intermetallic alloy with a thickness of 1.67 mu m.

We report on the comprehensive investigations of InAs/GaSb type-II superlattice (SL) with asymmetric and symmetric interfaces (IFs) formed using a migration-enhanced epitaxy (MEE) and an interrupted growth. The best structural and optical properties were observed for strain-balanced SL with asymmetric IFs grown using MEE at the bottom IF and continuous growth at the upper IF. The analysis of IF-related lines in Raman spectra of investigated SLs allowed for the evaluation of the quality of the InSb-like and GaAs-like interfaces. The thermal dependency of band gap energy was established from photoluminescence measurements according to the Varshni formula. The activation energies E1 and E2 for the dual-channel non-radiative recombination process were calculated. Linear characteristics of PL intensity vs. excitation power density were fitted using the relation IPL ∼ Eexck with different k. This allowed for the indication of dominant recombination mechanisms: radiative with a share of Auger process (k ≈ 0.8), pure radiative (k ≈ 1.0), and radiative with a slight share of Shockley–Read–Hall (k ≈ 1.1). Different behaviours of PL peak energy depending on the increase of excitation power density were observed: it was either blue-shifted, red-shifted, and/or a combination of both.

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 paper presents results of the characterisation of type I GaSb/AlSb superlattices (SLs) with a thin GaSb layer and varying thicknesses of an AlSb layer. Nextnano software was utilized to obtain spectral dependence of absorption and energy band structure. A superlattice (SL) with an energy bandgap of similar to 1.0 eV and reduced mismatch value was selected for experimental investigation. SLs with single (sample A) and double (sample B) AlSb barriers and a single AlSb layer (sample C) were fabricated using molecular beam epitaxy (MBE). Optical microscopy, high-resolution X-ray diffractometry, and photoluminescence were utilized for structural and optical characterisation. The presence of satellite and interference peaks in diffraction curves confirms the high crystal quality of superlattices. Photoluminescence signal associated with the superlattice was observed only for sample B and contained three low-intensity peaks: 1.03, 1.18, and 1.25 eV. The first peak was identified as the value of the energy bandgap of the SL. Other two peaks are related to optical transitions between defect states located at the interface between the SL and the top AlSb barrier. The time-dependent changes observed in the spectral characteristics are due to a modification of the SL/AlSb interface caused by the oxidation and hydroxylation of the AlSb layer.

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.

This Letter focuses on the 1/f noise properties of InAs/GaSb superlattice (SL), which is a promising material for infrared radiation detection and represents one of the alternatives to well-established bulk HgCdTe material. The InAs/GaSb SL material changes the conductivity type at temperature T approximate to 190 K, which has been correlated with measured 1/f noise. It was shown that 1/f noise comes from resistance fluctuations of linear noise sources. According to the electronic transport and 1/f noise models, the observed 1/f noise is connected with the hole conductivity component rather than the electron conductivity component, which is absent or at least immeasurable, even though electron conductivity governs the total conductivity of the InAs/GaSb SL. In the high-temperature region, the 1/f noise of InAs/GaSb SL is significantly smaller than that of InAs/InAsSb SL. The results favor InAs/GaSb SL material over InAs/InAsSb SL for photoconductive infrared detectors operating at room temperature.

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.

The paper covers some measurement aspects of transport of electrons through metals and semiconductors in magnetic field -magnetotransport -allowing for the determination of electrical parameters characteristic of three-dimensional (3D) topological insulators (TI) (i.e.those that behave like an insulator inside their volume and have a conductive layer on their surface).A characteristic feature of the 3D TI is also a lack of differences between the chemical composition of the conductive surface and the interior of the material tested and the fact that the electron states for its surface conductivity are topologically protected.In particular, the methods of generating strong magnetic fields, obtaining low temperatures, creating electrical contacts with appropriate geometry were presented, and the measurement methods were reviewed.In addition, the results of magnetotransport measurements obtained for two volumetric samples based on the HgCdTe compound grown with the molecular beam epitaxy method are presented.

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 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.

This paper concerns measurements and calculations of low frequency noise for semiconductor layers with four-probe electrodes. The measurements setup for the voltage noise cross-correlation method is described. The gain calculations for local resistance noise are performed to evaluate the contribution to total noise from different areas of the layer. It was shown, through numerical calculations and noise measurements, that in four-point probe specimens, with separated current and voltage terminals, the non-resistance noise of the contact and the resistance noise of the layer can be identified. The four-point probe method is used to find the low frequency resistance noise of the GaSb layer with a different doping type. For n-type and p-type GaSb layers with low carrier concentrations, the measured noise is dominated by the non-resistance noise contributions from contacts. Low frequency resistance noise was identified in high-doped GaSb layers (both types). At room temperature, such resistance noise in an n-type GaSb layer is significantly larger than for p-type GaSb with comparable doping concentration.

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.

The innovative two-step passivation by octadecanethiol (ODT) self-assembled monolayers (SAMs) and the following silicon dioxide (SiO2) deposition was used for the type-II InAs/GaSb superlattice photodetector. To understand the mechanism of passivation, the (100) GaSb surface covered with the ODT and, for comparison, with the biphenyl thiol (BPT), was characterized by the atomic force microscopy, Raman spectroscopy and contact angle analysis. The results of the study indicated the presence of the homogeneous both the ODT and the BPT monolayers; however, the ODT SAMs were more stable. Therefore, the ODT-based wet treatment was used in the two-step passivation resulting in a reduction of the dark current by one order of magnitude for passivated detector compared with an unpassivated device.

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.

The article presents selected aspects of the two-stage optimization of type II InAs/GaSb superlattice for the use in photodetectors of the long-wavelength-infrared radiation. The first stage was to develop the growth of the periodic structures confirmed by x-ray diffraction studies, and the second one to reduce density of the point defects on the superlattice surface. The effect of the thickness of InSb interfaces on the defect density and the impact of defects on the photoconductor properties was shown. The photoconductors with absorption cut-off wavlength of about 9.3 mu m and an current responsivity (Ri) detecteble in a wide temperature range of up to 225 K were obtained

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.

The empirical 1/f noise model for p ^+ -p-n infrared detector made of type-II InAs/GaSb superlattice material is presented. It is shown that 1/f noise magnitude can be accurately estimated if dark current contributions are determined and noise coefficients are known. It is found that the shunt, the bulk generation–recombination, and the trap-assisted tunneling currents contribute to the total 1/f noise. No 1/f noise connected with the diffusion and the band-to-band tunneling currents is observed.