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Content available remote Nanostructures with Ge–Si quantum dots for infrared photodetectors
In this paper questions of optimization of growth conditions in the method of molecular beam epitaxy for creation of high-efficient quantum dot infrared photodetectors are considered. As a model material system for theoretical investigations, heterostructures with germanium-silicon quantum dots on the silicon surface are chosen. For calculations of the dependencies of quantum dots array parameters on synthesis conditions the kinetic model of growth of differently shaped quantum dots based on the general nucleation theory is proposed. The theory is improved by taking into account the change in free energy of nucleation of an island due to the formation of additional edges of islands and due to the dependence of surface energies of facets of quantum dots on the thickness of a 2D wetting layer during the Stranski–Krastanow growth. Calculations of noise and signal characteristics of infrared photodetectors based on heterostructures with quantum dots of germanium on silicon are done. Dark current in such structures caused by thermal emission and barrier tunneling of carriers, as well as detectivity of the photodetector in the approximation of limitation by generation-recombination noises are estimated. Moreover, the presence of dispersion of quantum dots by size is taken into account in the calculations of the generation-recombination noises. Results of calculations of the properties of structures with quantum dots and their dependencies on growth parameters, as well as the characteristics of quantum dot photodetectors are presented. Comparison of the estimated parameters of quantum dots ensembles and the characteristics of quantum dot photodetectors with experimental data is carried out.
Content available remote Struktury na bazie ZnO do detekcji światła ultrafioletowego
W poniższej pracy, dwie struktury p-Si/n-ZnMgO zostały scharakteryzowane pod kątem zastosowania w detektorach światła ultrafioletowego (UV). Przeprowadzone zostały pomiary charakterystyk prądowo-napięciowych (I-V), fotoluminescencji (PL) oraz fotoodpowiedzi. Charakterystyki I-V zostały zmierzone w 310 K i pozwoliły stwierdzić, że obie struktury posiadają właściwości prostujące. Pomiary fotoluminescencji i fotoodpowiedzi zostały przeprowadzone w temperaturze pokojowej. Została przeprowadzona dokładna analiza widm fotoluminescencji, które w jednej z próbek ujawniły pasma emisyjne świadczące o obecności defektów. Pomiary fotoodpowiedzi również zostały szczegółowo przeanalizowane, podane zostały główne wady badanych struktur oraz rozwiązania, które mogą przyczynić się do udoskonalenia struktur.
In our paper, two p-Si/n-ZnMgO structures were characterized in terms of applicability in ultraviolet light detectors. A few measurement techniques have been applied: current-voltage (I-V) characteristics, photoluminescence (PL) and photoresponsivity measurements. I-V characteristics were measured at 310 K and allowed us to conlcude, that both of investigated structures have rectifying properties. Photoluminescence and photoresposivity measurements were performed at room temperature. The analysis of PL spectra exhibited emission bands corresponding to defects in one of studied samples. Photoresponsivity spectra were also thoroughly examined – the most important disadvantages of analysed structures were given together with possible solutions, which can be applied in order to obtain well-working UV detectors.
Content available remote Sensors on the Basis of PorSi for MEMS
We propose to use technology of electrochemical formation of low-dimensional porous silicon(porSi), which is compatible with the standard technologies of silicon VLSI, for creation of sensor part of MEMS "Lab-on-chip" type.
Double quantum well (DQW) (In,Ga)(As,N)/GaAs p-i-n photodetectors, grown by solid source molecular beam epitaxy using a radio-frequency plasma source for nitrogen with absorption for wavelengths above 870 nm have been investigated. The active region of the photodetectors contained two very thin absorption layers: 10.5 nm Ga(As,N) (structure #DP02) or 4 nm (In,Ga)(As,N) (#DP03). In spite of this, photodetectors exhibited high sensitivity (0.0525 A/W for 980 nm) for wavelength greater than the absorption edge of GaAs (870 nm). The dark current of photodetectors did not exceed 0.1 žA.
Content available remote Uncooled infrared photodetectors in Poland
The history and present status of the middle and long wavelength Hg1–xCdxTe infrared detectors in Poland are reviewed. Research and development efforts in Poland were concentrated mostly on uncooled market niche. Technology of the infrared photodetectors has been developed by several research groups. The devices are based on mercury-based variable band gap semiconductor alloys. Modified isothermal vapour phase epitaxy (ISOVPE) has been used for many years for research and commercial fabrication of photoconductive, photoelectromagnetic and other devices. Bulk growth and liquid phase epitaxy was also used. At present, the fabrication of IR devices relies on low temperature epitaxial technique, namely metalorganic vapour phase deposition (MOCVD), frequently in combination with the ISOVPE. Photoconductive and photoelectromagnetic detectors are still in production. The devices are gradually replaced with photovoltaic devices which offer inherent advantages of no electric or magnetic bias, no heat load and no flicker noise. Potentially, the PV devices could offer high performance and very fast response. At present, the uncooled long wavelength devices of conventional design suffer from two issues; namely low quantum efficiency and very low junction resistance. It makes them useless for practical applications. The problems have been solved with advanced 3D band gap engineered architecture, multiple cell heterojunction devices connected in series, monolithic integration of the detectors with microoptics and other improvements. Present fabrication program includes devices which are optimized for operation at any wavelength within a wide spectral range 1-15 µm and 200–300 K temperature range. Special solutions have been applied to improve speed of response. Some devices show picoseconds range response time. The devices have found numerous civilian and military applications.
Cathodoluminescence (CL) technique is applied for evaluation of in-depth and in-plane variations of light emission from semiconductor heterostructures, including laser diode structures. Light emission properties of heteroepitaxial and heteroepitaxial structures, are studied. We demonstrate possibility of in-depth profiling of complicated multi quantum well structures, which allows us to evaluate light emission characteristics from different regions of, e.g., laser structures. Due to this property of the CL, we can evaluate interconnections between structural quality of the samples and light emission characteristics. Stimulated emission under electron bean pumping is achieved in a conventional CL, set up for selected heterostructures. Thereshold currents for stimulated emission are evaluated from the CL investigations. We demonstrate that potential fluctuations are not fully screened in the active regions of laser structures, even at large excitation densities.
Most applications for radio frequency/microwave (thereafter called RF) transistors had been military oriented in the early 1980s. Recently, this has been changed drastically due to the explosive growth of the markets for civil wireless communication systems. This paper gives an overview on the evolution, current status, and future trend of transistors used in RF electronic systems. Important background, development and major milestones leading to modern RF transistors are presented. The concept of heterostructure, a feature frequently used in RF transistors, is discussed. The different transistor types and their figures of merit are then addressed. Finally an outlook of expected future developments and applications of RF transistors is given.
Content available remote HgCdTe epilayers on GaAs : growth and devices
View of basic and specific physical and chemical features of growth and defect formation in mercury cadmium telluride (MTC) heterostructures (HS's) on GaAs substrates by molecular beam epitaxy (MBE) was made. On the basis of this knowledge a new generation of ultra high vacuum set, ultra-fast ellipsometer of high accuracy and automatic system for control of technological processes was produced for reproducibility of growth MCT HS's on substrates up to 4'' in diameter. The development of industrially oriented technology of MCT HS's growth by MBE on GaAs substrates 2'' in diameter and without intentional doping is presented. The electrical characteristics of n-type and p-type of MCT HS's and uniformity of MCT composition over the surface area are excellent. The residual donor and acceptor centres are supposed as hypothetically tellurium atoms in metalic sublattice ("antisite" tellurium) and double-ionised mercury vacancies. The technology of fabricating focal plane arrays is developed. The high quality characteristics of infrared detectors conductance and diode mode are measured. Calculations of detector parameters predicted the improvement in serial resistance and detectivity of infrared diode detectors based on MCT heterostructures with graded composition throughout the thickness.
Content available remote Analysis of VLWIR HgCdTe photodiode performance
The performance of very long wavelength infrared (VLWIR) HgCdTe photodiodes at temperatures ranging from 77 K up to 150 K is presented. The effect of inherent and excess current mechanisms on quantum efficiency and dynamic resistance-area RA product is analysed. Different methods of determining the ideality factor are shown and among them the one based on the use of RA product versus bias voltage proves to be most reliable. At higher temperatures, however, the calculated ideality factor does not give any useful information about the nature of the p-n junction current due to significant influence of the series and shunt resistances. A comparison of the experimental data with the results of analytical and numerical calculations shows that the photodiodes with cut-off wavelength up to 14.5 um are diffusion-limited at temperatures exceeding 100K.
Issues relating to fabrication of VLWIR HgCdTe detectors with high performance and uniformity are reviewed. The primary mechanism operative in the activation of p type dopants in HgCdTe is discussed along with implications for fabrication of high performance detectors. Origin of native defect related deep centres in limiting the minority carrier lifetime is explored.
Content available remote Inherent and additional limitations of HgCdTe heterojunction photodiodes
The performance of P-on-n double-layer heterojunction (DLHJ) HgCdTe photodiodes at temperature of 77 K is presented. The effect of inherent and excess current mechanisms on quantum efficiency and R₀A product is analysed. The diodes with good R₀A operability, high quantum efficiency, and low 1/f noise have been demonstrated at cutoff wavelengths up to 14 mm. The experimental results show that proper surface passivation and low series/ contact resistance are major issues relating to fabrication of HgCdTe detectors with high performance.
During the past decade, group III-Nitride wide bandgap semiconductors have become the focus of extremely intensive reearch because of their exceptional physical properties and their high potential for use in countless numbers of applications. Nearly all aspects have been investigated, from the fundamental physical understanding of these materials to the development of the fabrication technology and demonstration of commercial devices. The purpose of this paper is to review the physical properties of III-Nitrides, their areas of application, the current status of the material technology (AlN, AlGaN, GaN, GaInN) including synthesis and processing. The state-of-the-art of III-Nitride material quality, as well as the devices which have been demonstrated, including electronic devices, AlxGa₁-xN ultraviolet photoconductors, ultraviolet photodiodes, visible light emitting diodes (LEDs) and ultraviolet - blue laser diodes, will also be presented.
Content available remote Luminescence of porous silicon and porous silicon encapsulated structures.
Spectroscopic properties of encapsulated porous silicon (PS) have been studied in detail. In order to investigate different heterostructures of porous silicon a complex of analysis methods such as photoluminescence (PL) electroluminescence (EL), cathodoluminescence (CL) and thermostimulated depolarisation (TSD) were applied. The process of light emission shows a tendency to decrease. This decrease varies for different kinds of luminescence. The EL intensity dynamics depends on polarization effects in porous silicon.
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