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1

Quantum yield enhancement in AlGaN(n)/GaN(p) UV photodetector with position-dependent energy band gap

100%

Małachowski M. J.

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tom Vol. 49, nr 6

31-43

EN

Numerical analysis has been carried out on the spectral dependence of the quantum yield for an AlGaN(n)-GaN(p) photodiode ultraviolet (UV) detector in which the AlGaN layer has position-dependent band gap. The spatial dependence of the material properties, such as energy band-gap and absorption coefficient of the photodiode's n-type layer is considered in the calculation. The band-gap grading with a proper direction, due to a reduced absorption coefficient at the surface region and the built in electric field, results in the increase of the minority carrier generation in the vicinity of the junction resulting the enhancement of carrier collection efficiency. In order to improve the quantum yield, it was found that there is no need to fabricate the structures exhibiting the large gradients. In case of no surface recombination, there is a substantial rise in the detector quantum yield with increasing the grading within the range of small values of the gradient. Much more extended the dependence in quantum yield with the grading has been found when the recombination was present at the illuminated surface. The carried out study enabled to determine the optimal grading and the graded layer thickness with regard to the detector response to the selected UV wavelengths.

PL

Dokonano analizę numeryczną spektralnej zależności wydajności kwantowej w zakresie ultrafioletowym (UF) fotodiody AlGaN(n)/GaN(p), w której warstwa AlGaN(n) jest półprzewodnikiem o zależnej od położenia przerwie energetycznej. W obliczeniach uwzględniono zależność od szerokości przerwy energetycznej współczynnika absorpcji w zakresie UF. Zastosowanie materiału z odpowiednio ukierunkowanym gradiantem przerwy energetycznej, powoduje wzrost wydajności zbierania w obszarze złącza generowanych przez światło nośników mniejszościowych, bowiem gradient wywołuje wytworzenie się w półprzewodniku dodatkowego pola elektrycznego oraz zmniejszenie absorpcji w pobliżu powierzchni. W celu zwiększenia wydajności kwantowej nie zachodzi konieczność wykonywania warstw o dużym gradiencie - co zmniejszyłoby ruchliwość nośników. W przypadku zaniedbywalnej rekombinacji powierzchniowej, stwierdzono że już w zakresie małych gradientów występuje znaczący wzrost wydajności kwantowej ze wzrostem wartości gradientu. W przypadku natomiast obecności rekombinacji powierzchniowej, występuje także wzrost wydajności kwantowej ze wzrostem gradientu lecz ten wzrost jest powolniejszy niż w przypadku poprzednim. Rezultaty wyliczeń umożliwiają określenie optymalnego gradientu oraz grubości warstwy z gradientem przerwy energetycznej ze względu na odpowiedź detektora na promieniowanie UF o dowolnie wybranych zakresach długości fal.

2

Basic features of the laser acceleration of charged particles

63%

Małachowski M. J. , Dubik A.

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tom Vol. 49, nr 2

412--420

EN

Purpose: of this paper is to study the acceleration of the charged particles by the laser beam in the range outside the resonance conditions. The studies have been limited in the subresonance region since in order to achieve the resonance acceleration a very high constant magnetic field is needed. Design/methodology/approach: The studies are carried out using the analytical derivations of the particles dynamics and its kinetic energy. The evolution of the acceleration process in time has been studied. The presented illustrations enabled interpretation of the obtained equations. Findings: The kinetic energy of the particle periodically achieves the maximal energy. Its value and the distance between the subsequent maxima rise with the increasing magnetic field or the laser beam intensity. However, these parameters of oscillating energy decrease with the decreasing wavelength. Research limitations/implications: Limits in the energy of accelerated particles are caused by the limits of the available at present the laser beam energy and the static magnetic field intensity. Practical implications: The authors of this paper believe that the presented results of the studies will help the designing of the experimental studies. It has been shown the way of achieving the high energy particles without the application of a very high magnetic field. Originality/value: The value of the paper is the analytical derivation of the parameters describing the oscillatory shape of the particles energy and numerical analysis its course. According to the authors best knowledge there are no performed such analysis of the acceleration process.

3

Impact of the mass and other parameters of charged particles on the results of laser resonance acceleration

63%

Dubik A. , Małachowski M. J.

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tom Vol. 63, nr 1

13-42

EN

Theoretical and numerical analyses are presented concerning the conditions at which the charged particles of different masses can be accelerated to significant kinetic energy in the circularly polarized laser or maser beams and a static magnetic field. The studies are carried out using the analytical derivations of the particles dynamics and theirs kinetic energy. The presented illustrations enabled interpretation of the complex motion of particles and the possibilities of their acceleration. At the examples of an electron, proton and deuteron, the velocity, kinetic energy and trajectory as a function of the acceleration time at the resonance condition are illustrated in the appropriate graphs. The particles with larger masses require the application of enhanced magnetic field intensity at the resonance condition. However, this field intensity can be significantly reduced if the particles are preaccelerated.

PL

Stosując metody teoretyczną i numeryczną przebadano warunki, w których naładowane cząstki o rożnych masach można przyspieszać do znacznej energii w kołowo spolaryzowanej laserowej bądź maserowej wiązce z dodatkowym statycznym polem magnetycznym. Badania przeprowadzono za pomocą wyprowadzonych analitycznych relacji dotyczących dynamiki i kinetycznej energii cząstek. Dzięki stosunkowo licznym wykresom stała się możliwa interpretacja dość złożonego ruchu cząstek oraz przebiegu ich akceleracji. Na przykładach elektronu, protonu i deuteronu zostały zilustrowane zależności od czasu trwania akceleracji takich wielkości jak kształt trajektorii oraz kinetyczna energia. Wszystkie ilustracje dotyczą warunku rezonansu, czyli synchronizacji ruchów obrotowych cząstki i wektora natężenia pola elektrycznego. Czym większa masa cząstki, tym większe natężenie stałego pola magnetycznego jest niezbędne do uzyskania warunku synchronizacji. Jednak to natężenie można znacznie zredukować, jeśli cząstka będzie posiadała prędkość początkową.

4

Photoresponse of GaN p-n junction and Schottky barrier ultraviolet photodetectors

63%

Małachowski M. J. , Rogalski A.

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tom Vol. 6, No. 2

141-149

EN

At present, the main effors in fabrication of UV photodetectors are directed to GaN Schottky barriers and p-n junction photodiodes. The future development of UV photodetectors will be dominated by complex band gap heterostructures using 3- dimensional gap and doping engineering. AlGaN exhibits extreme flexibility, it can be tailored for the optimised detection at important region of UV spectrum, and multicolor devices can be easily constructed. A study of GaN Schottky barriers (with a n-type material) and p-n junction photodiodes in ultraviolet range are carried out. Due to the fact that the built-in voltage of a Schottky diode is smaller than that of a p-n junction, the depletion region width is smaller than that of p-n junction. Special attention has been devoted to an analysis of the current responsivities of both types of detectors. Owing to relative simplicity in fabrication of Schottky barriers, they can be more promising than p-n junction detectors, especially in the case of low doping or/and thin front layer ensuring the entire depletion of the n-type layer.

5

Impact of the chirping effect on charged particle acceleration in laser radiation

63%

Małachowski M. J. , Dubik A.

Journal of Achievements in Materials and Manufacturing Engineering

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2011

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tom Vol. 48, nr 1

87--96

EN

Purpose: The aim of this paper is to find in a numerical way the trajectories and kinetic energies gained by electrons, protons and deuterons accelerated in the laser or maser chirped radiation propagating in a vacuum, with an additionally applied external static axial magnetic field. The accelerated particles to the well defined energies are of interest in many applications, among others in medicine or in processing of different materials. Design/methodology/approach: The acceleration processes of electrons, protons and deuterons were found to be strongly depending on the way the frequency of the laser or maser radiation changes in time. In order to design the realistic acceleration processes the appropriate parameters of a laser or maser and a static magnetic field were used. Findings: The quantitative illustrations of the calculation results in a graphical form enable to discuss the impacts of the chirping effect on the acceleration process of electrons, protons and deuterons. It was found that the rate at which a particle gains the energy depends not only on the particle’s mass but also on the laser radiation frequency variation rate. Due to the different rate at which a relativistic mass of an electron, proton or deuteron increases during the acceleration process the rate at which chirped frequency decreases in time should be different. Research limitations/implications: Limits in the gained energy by the accelerated particles are a consequence of the limits in the available at present the laser or maser beam energy and the static magnetic field intensity. Originality/value: The authors have found, in an exact numerical way, the values of the acceleration equipment parameters which should be applied to obtain the desired energy of the accelerated particles. It is explained why the rate at which a particle gains the energy depends on the way the radiation frequency varies in time.

6

Resonance acceleration of a charged particle in a laser beam and static magnetic field

63%

Dubik A. , Małachowski M. J.

Journal of Technical Physics

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2009

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tom Vol. 50, no 2

97-120

EN

Conditions at which the charged particles can be accelerated to the significant energies under interaction with the laser or maser radiation and the static magnetic field have been studied. The studies have been performed on the basis of the derived by the author's analytical solutions. With the example of an electron, the trajectory, velocity and kinetic energy as a function of the acceleration time have been shown. We have defined the maximal static magnetic field which was found to be appropriate to achieve the resonance condition in the acceleration process. At certain values of the magnetic field, the projections of the 3-dimensional trajectory onto the plane perpendicular to the axis show quite regular curves in the shape of epicycloids or hypocycloids with convex and concave bows, respectively. In the resonance region, there appears an increase in effectiveness of the energy transfer from the electromagnetic field to the accelerated particle and it can be realized simply through a very small increase of magnetic induction. The significant gain of the energy by the accelerated electron occurs only in the case of inversely directed laser beam velocity and the static magnetic field. The maximal energy can be increased by rising the laser beam or the magnetic field intensities. The energy gained by an electron depends on the acceleration time and it increases until the maximum energy is reached. The distance the electron covers to gain the maximal energy, depends on the intensities of the laser beam and the static magnetic field, and on the acceleration time. The analysis of acceleration process in the maser beam shows many advantages arising from the longer wavelength radiation emitted. The essential advantage is connected with the reduction of the static axial magnetic field intensity.

7

New organic photochromic materials and selected applications

63%

Żmija J. , Małachowski M. J.

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tom Vol. 41, nr 1-2

48-56

EN

Purpose: The aim of this work is to perform the review of the recent most important results of experimental and theoretical investigations connected with the photochromic materials and their selected applications. Design/methodology/approach: The recent achievements in the field of designing and preparation methods of organic photochromic materials and devices operating as tree-dimensional optical data storage. Findings: We pointed out the important role that play the photochromic effect in organic materials and which can be used as the above mentioned devices. Research limitations/implications: The main disadvantage of organic materials are reported to be to short their lives and weak resistivity to the moist but the improvements are advancing. Originality/value: Our review concerns the most recent findings in this area. We also show some recent examples of photochromic organic material application in 3D memory devices.

8

Difference in acceleration of electrons, protons and deuterons in a laser beam

63%

Małachowski M. J. , Dubik A.

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tom Vol. 41, nr 1-2

82-90

EN

Purpose: The aim of this paper is to find in a numerical way the main differences in the trajectories and kinetic energies of electrons, protons and deuterons accelerated in the laser or maser beams propagating in a vacuum, with an additionally applied external static co-axial magnetic field. The accelerated particles to the well defined energies are of interest in many applications, among others in medicine or in processing of different materials. Design/methodology/approach: Due to differences in masses the comparison between the acceleration processes of electrons, protons and deuterons is possible to perform after appropriate parameters of radiation of a laser, maser and a static magnetic field have been designed. Findings: The quantitative illustrations of the calculation results in a graphical form enable to discuss the main differences in the acceleration process of electrons, protons and deuterons. It was found that the rate at which a particle gains the energy depends not only on the particle’s mass but also on the stage of the process. Due to the mass differences, in order to keep a particle inside the radiation beam, significantly different static magnetic fields should be used to each kind of a particle. The authors have found an answer to the question why the rate at which particles energy increases in time, is different for different particles and why the difference depends on a stage of the acceleration process. Research limitations/implications: Limits in the energy of accelerated particles are caused by the limits of laser or maser beam energy or power available at present and the static magnetic fields. Originality/value: The authors show, in an exact numerical way, the values of the acceleration equipment parameters which should be selected to obtain the desired energy of the accelerated particles. It is explained why the rate at which a particle gains the energy depends on the stage of the process and on the particle’s mass.

9

Organic field-effect transistors

63%

Małachowski M. J. , Żmija J.

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tom Vol. 18, No. 2

121-136

EN

The paper reviews the recent year publications concerning organic field-effect transistors (OFETs). A lot of works have been performed to help understanding the structural and electrical properties of materials used to construct OFETs. It has been established that in partially ordered systems, the charge transport mechanism is thermally activated and field-assisted hopping transport and the hopping transport between disorder-induced localized states dominate over intrinsic polaronic hopping transport seen in organic single crystals. Many research attempts have been carried out on the design of air-stable organic semiconductors with a solution process which is capable of producing OFETs with excellent properties and good stability when subjected to multiple testing cycles and under continuous electrical bias. Recent experiments have demonstrated ambipolar channel conduction and light emission in conjugated polymer FETs. These achievements are the basis for construction of OLED based displays driven by active matrix consisting of OFETs.

10

Materiały organiczne w elektronice

45%

Żmija J. , Małachowski M. J. , Zieliński J. , Wacławek M. , Ścieżka K.

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tom R.11, NR 1-2

69--80

PL

Przedstawiono przegląd wykorzystania materiałów organicznych w optoelektronice. W ostatnich latach widoczne są znaczne postępy w tym względzie zarówno naukowe, jak i aplikacyjne. Stwarza to realne podstawy, aby sądzić, że powstaje nowa licząca się gałąź nauki powiązana z interesującymi zastosowaniami, które w zakresie ciekłych kryształów (CK) są realizowane od dawna. Najnowsze publikacje pokazują niewątpliwe perspektywy inżynierii materiałowej w badaniach oraz zastosowaniu stałych półprzewodników organicznych. Omówiono ostatnie osiągnięcia w konstrukcji displejów CK, fotoogniw, ogniw słonecznych, emiterów LED, laserów oraz elementów mikroelektronicznych, zwłaszcza cienkowarstwowych tranzystorów.

EN

Review of papers connected with wide aspects of organic material engineering and its application in optoelectronics is presented. It creates an actual basis for new important branch of science and technology, which in LC case has been realized for decades already. Last achievements in fabrication of LC displays, photoelements, solar cells, OLEDs, lasers and microelectronic devices especially thin film transistors are presented. It is evident that a significant progress in science, technology and application of organic materials has been achieved.