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  1. 67 Acta Physica Polonica A

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  1. 6 Korona K.

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1
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Charge Carrier Generation Caused by X-Rays in Organometallic Materials

100%
Godlewski J., Signerski R., Jarosz G., Stizza S., Berrettoni M.
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vol. 96
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issue 2
295-301
EN
Organometallic compounds play an exceptional role among organic compounds. Due to their structure a number of these compounds demonstrate interesting properties in various phenomena. Organometallic compounds show special properties in the case of X-ray absorption owing to considerable differences between the absorption coefficients of metals and light elements. The analysis of processes of charge carrier generation as a result of X-ray absorption in chosen organometallic compounds is the subject of this paper. Spectral dependences of charge carrier photogeneration efficiency around the Cu K-edge in copper phthalocyanine and copper acetylacetoniane have been specially considered. It has been observed that the photocurrent spectrum in these materials follows the absorption spectrum but mutual relation is not directly proportional. Experimental results connected with current-voltage and current-intensity characteristics have been analysed, as well. The obtained relationships have been compared with adequate results connected with charge carrier photogeneration in visible area and UV in organic materials. It has been observed that the X-ray photogeneration of charge carriers in the examined range of energy differs from the mechanisms of charge carrier generation in visible area and UV. The basic differences arise from the participation of secondary electrons, which are generated due to Auger electrons, Compton effect, and metal fluorescence. The process of charge carrier generation as a result of X-rays absorption is characterized by strong recombination of charge carriers in channels in which charge carriers are generated by high energetic secondary electrons.
2
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Diffusion Length Studies in CdMnTe by the Surface Photovoltage Method

100%
Płaczek-Popko E., Szaro L., Jędral L.
Acta Physica Polonica A
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1991
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vol. 79
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issue 2-3
187-190
EN
The surface phototovoltage method provides a nondestructive means of measuring minority carriers diffusion length and is suitable for process control applications and for material acceptance tests. Application of the method in the case of CdMnTe compounds has been studied in the present paper. The optimum measurement conditions have been investigated by studying the dependence of measured diffusion length on the experimental conditions. As the surface photovoltage method requires the exact values of absorption coefficient as a function of wavelength, α = f(λ), the dependence has been determined. The minority carrier diffusion length for the sample investigated has been found to be equal to several tenth of μm.
3
Content available remote

Numerical Analysis of Photoenhanced Electric Currents in Molecular Materials

100%
Jarosz G., Signerski R., Godlewski J.
Acta Physica Polonica A
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1995
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vol. 87
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issue 4-5
855-860
EN
This paper presents numerical calculations of photoenhanced current-applied voltage and photoenhanced current-light intensity characteristics with regard to the exciton diffusion length, lifetime of excitons and rate of exciton surface quenching. Dependencies of this type cannot be obtained an­alytically. It is shown that the increase in diffusion length causes the decrease in current in the case of strong surface quenching of excitons. Simultaneously, it is shown that the quality of crystals influences the photoenhanced current. A better quality of crystals causes the increase in the current in the case of weak surface quenching of excitons.
4
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Space Charge Limited Currents in Anthracene Crystals under Modulated Illumination

100%
Uzarczyk A., Godlewski J.
Acta Physica Polonica A
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1995
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vol. 87
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issue 4-5
849-854
EN
Space charge limited currents have been examined in anthracene crys­tals illuminated with a chopped beam of monochromatic light (λ = 420 nm). The beam was uniformly absorbed in the anthracene crystal. The primary objective of our research was to determine mechanisms responsible for the release and trapping of charge carriers in the case of space charge limited currents as a function of time. The experimental results concern the depen­dences of photocurrents on the frequency of light chopping, light intensity, voltage and current decay after illumination. Photocurrent decay as a func­tion of time was exponential for short time periods (i.e. for milliseconds), while for longer periods it was described by the power function t^{-1/l}, where parameter 1 is the characteristic parameter of the exponential distribution of traps.
5
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Electric Current Flow through Tetracene Layer-Anthracene Crystal Junction

100%
Signerski R., Godlewski J., Sodolski H.
Acta Physica Polonica A
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1995
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vol. 87
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issue 4-5
843-847
EN
Theoretical and experimental analysis was carried out on electric cur­rents limited by the potential barrier governing the flow of holes from the tetracene layer to the anthracene crystal. Theoretical spatial distributions of charge carriers near the barrier were determined, as well as current-field dependences for the currents flowing through the investigated junction in the presence and in the absence of illumination. A current-field character­istic of the junction conditioned current is described by dependence of the j ∝ E³_{0} type in the presence of illumination and by the j ∝ E^{2l+1}_{0} type in the lack of illumination, where l is the characteristic parameter of the trap distribution. Experimental research of the hole currents flowing through the polycrystalline tetracene layer-anthracene monocrystal junction confirmed the theoretical predictions about the current-field characteristics. A remark­ably unequivocal confirmation was obtained for the current-field dependences in the presence of illumination.
6
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Fast Detection of Infrared Laser Pulses on Planar Small Area GaAs/AlGaAs Heterojunction

63%
Širmulis E., Kazlauskaitė V., Gradauskas J., Sužiedėlis A., Ašmontas S.
Acta Physica Polonica A
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2008
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vol. 113
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issue 3
851-854
EN
We report the first experimental observation of fast photovoltage in small area GaAs/AlGaAs heterojunction planar detector induced by nanosecond CO_2 laser pulses. This device revealed itself as a sensitive detector of millimeter waves and as a fast IR sensor operating at room temperature. Taking into account fast response of the detector and close to linear voltage-power dependence, the results are interpreted by photoemission of hot carriers over the potential barrier of the heterojunction.
7
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Optical Studies of HgCdMnTe Bicrystals

63%
Grabecki G., Wróbel J., Karczewski G.
Acta Physica Polonica A
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1991
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vol. 79
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issue 2-3
221-223
EN
We report preliminary results of optical measurements performed on Hg_{1-x-k}Cd_{x}Mn_{k}Te grain boundaries. Photovoltaic spectra and I-V characteristics under illumination exhibit metastable behavior, confirming our previous conclusions based on transport measurements under high hydrostatic pressure.
8
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Photogalvanic Effect in Semiparabolic Quantum Well

63%
Majchrowski K., Paśko W., Tralle I.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
854-856
EN
In this work we studied the charge carriers behaviour in quantum structures where the symmetry with respect to space coordinates and time-reversal symmetry are broken simultaneously. As the model of such structures we considered finite semiparabolic quantum well (we considered earlier the case of triangular QW) placed in external magnetic field. We have shown by numerical analysis that the energy spectra of charge carriers in such structures are anisotropic with respect to in-plane (transverse) motion ϵ_{n}( + k_{x}) ≠ ϵ_{n}(-k_{x}). This leads to the anisotropy of charge carriers in-plane momentum transfer which, in its turn leads to the anisotropy of photoconductivity σ( + k_{x}) ≠ σ(-k_{x}) and as it follows from our calculations, the effect though not very great, could be measurable for the magnetic field of about few T.
9
Content available remote

Photo-Effects in In/p-CuInSe_{2} Schottky-Type Junction

63%
Opanowicz A., Kościelniak-Mucha B.
Acta Physica Polonica A
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1991
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vol. 79
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issue 2-3
411-414
EN
The voltage-dependent photocurrent and the short-circuit photocurrent generated by the modulated light in the In/p-CuInSe_{2} junction were measured. The results suggest that the recombination of carriers occurs in the metal-semiconductor interface as well as in the recombination centres present in the space charge region of the junction. Both the interface recombination and the recombination in the centres can be modified by illumination of the junction.
10
Content available remote

Mercury Zinc Telluride 10.6 µm Ambient Temperature Photodetectors

63%
Piotrowski J.
Acta Physica Polonica A
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1991
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vol. 80
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issue 5
751-765
EN
Theoretical and experimental investigations of mercury zinc telluride (MZT) ambient temperature longwavelength photodetectors are reported. The ultimate detectivities of MZT photoconductors (PC), photodiodes, photoelectromagnetic (PEM) and Dember detectors at 10.6 μm have been calculated as a function of material composition, doping and geometry of the devices. The high-temperature longwavelength PC and PEM detectors have been fabricated from Cu-doped bulk MZT crystals grown by a modified quench/anneal technique. The measured performance has been confronted with theoretical predictions showing good overall agreement. It is concluded that the high figure of merit, stability and hardness of MZT make this material superior in comparison to mercury cadmium telluride and that it will replace the latter in application for high-temperature photodetectors. The performance of high-temperature MZT photodetectors can be further improved by the use of optical resonant cavity and optical immersion. These devices exhibit detectivity by several orders of magnitude higher than thermal detectors with subnanosecond response time, and can achieve performance comparable to that of slow thermal detectors.
11
Content available remote

Anisotropy of the Conductivity in the Asymmetric Quantum Wells

63%
Majchrowski K., Paśko W.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1241-1246
EN
Gorbatsevich et al. and Kibis suggested that a number of interesting galvano-magnetic effects could be observed in quantum structures where the symmetry with respect to the space coordinates inversion and time-reversal are broken simultaneously. In the paper of Kibis for example, the infinite triangular quantum well in an external magnetic field was considered and the anisotropy of electron momentum transfer due to interaction with phonons was predicted. The role of magnetic field was to provide the time-invariance breaking. In this work we considered the effect of anisotropy of electron momentum transfer due to interaction with polarized light using more realistic model of finite triangular quantum well. This anisotropy leads to the anisotropy of the real part of photoconductivity and as it follows from our calculations, the effect though not very great, could be measurable for the attainable values of magnetic field B≈5 T and the widths of quantum well.
12
Content available remote

Photoelectronic Processes in ZnSe:Cu Single Crystals

63%
Firszt F.
Acta Physica Polonica A
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1992
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vol. 82
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issue 5
893-895
EN
Measurements of steady state and transient stimulation and quenching of photocurrent and luminescence were performed in ZnSe single crystals doped with Cu which exhibit marked change in the photoconductivity and luminescence when illuminated by infrared light simultaneously with shorter wavelength radiation. A model which might explain all IR induced phenomena on the basis of donor-acceptor pair recombination mechanism including releasing holes from deep center by IR light and energy redistribution between different recombination centers is presented.
13
Content available remote

Magnetoresistance of n-CdTe in the "Persistent" State

63%
Kossacki P., Karpierz K.
Acta Physica Polonica A
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1993
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vol. 84
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issue 4
737-740
EN
In this paper we present results of measurements done on photoexcited carriers in high purity n-CdTe at liquid helium temperature. The photocurrent under near band gap illumination was measured, as well as the long term (≈ 15 hours) photoconductive decay after switching off the light. The transverse magnetoresistance was measured in high magnetic fields in two cases: 1) under external illumination, 2) in the "persistent" state after ≈ 15 h of photocurrent decay. It was shown that in high magnetic fields this magnetoresistance exhibits a quadratic dependence on magnetic field (Δρ/ρ ≈ B^{2}) in both cases.
14
Content available remote

Transport of Photoexcited Electron-Hole Plasma in GaN/AlGaN Quantum Well

63%
Korona K., Caban P., Strupiński W.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
927-929
EN
We report spatially resolved photocurrent measurements showing transport of excitation on long distances in plane of a 6 nm GaN/Al_{0.1}Ga_{0.9}N quantum well. The strong field present in nitrides (due to large spontaneous and piezoelectric polarizations) leads to lower recombination rates of electrons and holes, so in the case of electron-hole pairs excited by light, relatively long-lived electron-hole plasma could be generated. In the case of the investigated quantum well, lifetime of few μs was expected. The thermal measurements showed that barriers were low enough, so all excited carriers could reach the electrode (thermal activation energy of 0.11 eV was found). The diffusion length for unbiased structure was about 40 μm. It was observed that the charge transport could be clearly accelerated by bias. In the biased quantum well, the transport range was of the order of 100 μm under both positive and negative bias. The reported effect of long transport range is very important for electronic devices made on the GaN/AlGaN structures.
15
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Content available

Photoluminescence and Photoconductivity Dynamics in Semi-Insulating Epitaxial GaN Layers

63%
Gaubas E., Juršėnas S., Kazlauskas K., Miasojedovas S., Vaitkus J., Žukauskas A.
Acta Physica Polonica A
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2005
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vol. 107
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issue 1
215-219
EN
The transients of fast free-carrier recombination and of multi-trapping processes due to different species of defects have been investigated by photoluminescence and by contact and microwave photoconductivity. Three distinct stages of relaxation, namely, of stimulated emission, of recombination due to point defects and capture into trapping centers associated with dislocations, and a non-exponential stage with a stretched-exponent asymptotic decay ascribed to dislocations mediated multi-trapping were distinguished by correlated examination of time-resolved photoluminescence and photoconductivity transients.
16
Content available remote

Transient Photo-Induced Current Measurements in High Resistivity ZnSe Crystals

63%
Bała W., Firszt F., Dul D., Turlo Z., Borkowski J.
Acta Physica Polonica A
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1991
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vol. 79
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issue 2-3
295-298
EN
Using technique of computerized signal-averaging of photocurrent transient, we have studied the details of deep level states in high resistivity ZnSe crystals. The time resolved spectra of photocurrent and four-gate PICT spectra are presented.
17
Content available remote

Optical Parameter Analysis of Thin Absorbing Films Measured by the Photovoltage Method

63%
Pavelka R., Hlávka J., Ohlídal I., Sitter H.
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EN
A special method for measuring the optical parameters of thin absorbing films is presented. Within the method the radiation transmitted through the layer is measured. The transmitted radiation is detected by the space charge region which is located in the substrate at the interface with the layer. The space charge region acts as a photodetector placed just behind the layer. In this paper the method is applied to characterize a system of an absorbing ZnSe film on a GaAs substrate. The values of the optical parameters of the film are evaluated. This means that the value of the thickness and the spectral dependences of both the refractive index and extinction coefficient are determined. The spectral dependences of both optical constants are determined in the visible range. Finally, the comparison of our results obtained by this method with the results obtained from ellipsometric and reflectance measurements is presented.
18
Content available remote

Photoneutralization of the Fe^{3+} Centers in the ZnSe Crystals Heavily Doped with Iron

63%
Lubomirska-Wittlin A., Szadkowski A. J., Demianiuk M.
Acta Physica Polonica A
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1991
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vol. 79
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issue 2-3
337-340
EN
Photoconductivity and optical quenching of the photoconductivity were measured. The photoneutralization of the Fe^{3+} centres has been found to occur for photon energies down to 0.8 eV (i.e. the threshold can not be at 1.1 eV, as often quoted). The conclusion from our previous paper that the lattice relaxation energy is small, has been confirmed. It has to be smaller than 0.1 eV.
19
Content available remote

Modeling and Simulation of a Photovoltaic Module in Different Operating Regimes

63%
Jadallah A., Mahmood D., Abdulqader Z.
Acta Physica Polonica A
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2015
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vol. 128
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issue 2B
B-461-B-464
EN
Modern research focuses on the renewable energy sources such as solar energy. This paper presents the modeling and performance of a photovoltaic (PV) cell. A simulation code is built using MATLAB. Results show that the increase of solar radiation and of ideality factor of diode lead to an increase in the output power of PV module, while the increease of cell temperature and of the dark saturation current lead to a decrease of the power. Curves of I-V and P-V dependencies are presented for module having 50 branches connected in parallel, with each branch having 50 cells connected in series. Data for certain Iraqi governorates are taken and applied for proposed module.
20
Content available remote

Electrical Properties of Hydrogenated Amorphous Si_{1-x}Ge_{x} Thin Films

51%
Pisarkiewicz T., Stapiński T., Kołodziej A.
Acta Physica Polonica A
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1991
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vol. 79
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issue 2-3
203-206
EN
Thin films of hydrogenated amorphous Si-Ge alloys were obtained by r.f. sputtering in Ar + H_{2} gas atmosphere using composite targets of Si and Ge. Dark conductivity and photoconductivity were measured in the temperature range of 300-500 K for films with x varying from 0.11 to 0.63. Both dark conductivity and photoconductivity exibit activation type dependences in the temperature range studied. Heterogeneity two-phase model and a model based on Fermi level shift with temperature were invoked to discuss the conduction mechanism.
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