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1
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Application of Kelvin Probe Microscopy for Nitride Heterostructures

100%
Bożek R.
Acta Physica Polonica A
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2005
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vol. 108
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issue 4
541-554
EN
Kelvin probe microscopy is an experimental technique designed to investigate fluctuations of surface potential (work function per electron) related to distribution of electric charge or variations in composition. The paper describes principle and precision of measurements. The results obtained for group-III nitrides semiconductor heterostructures grown on c-plane sapphire by metal-organic vapour phase epitaxy are presented. The observations concerns defects: inversion domains for Ga- and N-polar layers, threading dislocations and effects of spontaneous polarization leading to 2D carrier gas. To achieve insight in the evolution of defects, bevelled and cross-sectioned samples were investigated along with surface of "as grown" layers. Applicability of standard Kelvin probe microscopy method was also extended by investigating dependence of the surface potential on variable wavelength illumination, offering opportunity for spectroscopy of individual defects.
2
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Photoreflectance Measurements of InGaAs/GaAs Quantum Wells

52%
Tomaszewicz T., Korona K., Bożek R., Baranowski J.
Acta Physica Polonica A
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1996
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vol. 90
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issue 5
965-968
EN
Samples with InGaAs/GaAs quantum wells were grown by metallo-organic chemical vapour deposition in order to detect and analyze GaSb islands deposited on the surface. Results of photoreflectance measurements of quantum wells are reported. The correspondence between broadening of quantum well transition lines and GaSb structures has been observed.
3
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Microscopic Investigation of SiC Epitaxial Layers οn On-Axis 4H-SiC Substrates Using Kelvin Probe Force Microscopy

52%
Kościewicz K., Bożek R., Strupiński W., Olszyna A.
Acta Physica Polonica A
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2009
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vol. 116
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issue S
S-69-S-71
EN
We report on Kelvin probe force microscopy and electron backscatter diffraction measurements of 3C-SiC epitaxial layers grown on exactly oriented Si-face 4H-SiC (0001) substrates in a horizontal hot-wall chemical vapor deposition reactor, in the temperature range from 1150°C to 1620°C, under H_{2} or H_{2} +SiH_{4} atmosphere. The investigated layers were doped with nitrogen (for n-type) and aluminium (for p-type). The electron backscatter diffraction analysis revealed structure of polytype 3C blocks with a relative rotation of 60 and/or 120°. The Kelvin probe force microscopy measurements revealed cubic substructure as a equilateral triangle objects contrast which is characteristic of 3C silicon carbide polytype. The surface potential contrast was found to be dependent on the type and concentration of doping, which could be explained in terms of the impurities accumulation at block boundaries.
4
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Hydrostatic Pressure Spectroscopy of the Vanadium Luminescence in GaAs

52%
Wysmołek A., Bożek R., Babiński A., Hennel A.
Acta Physica Polonica A
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1992
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vol. 82
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issue 5
837-840
EN
We report luminescence measurements of the intracenter transition ^{3}T_{2} → ^{3}A_{2} of the V^{3+}(3d^{2}) charge state in semi-insulating GaAs under hydrostatic pressure up to 0.8 GPa at liquid helium temperature. The hydrostatic pressure coefficient of the zero-phonon line is found to be equal to 6.9 ± 0.2 meV/GPa. This result enables us to determine the Huang-Rhys parameter, which characterizes the coupling to the symmetric mode of vibration, as S_{A} = 1.4 ± 0.1. Using this parameter, computer simulation leading to a reconstruction of the shape of both luminescence and corresponding absorption spectra were performed.
5
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"Excitonic" and Photoionization Absorption Spectra of Iron in III-V Materials

52%
Wysmołek A., Tryc R., Bożek R., Hennel A.
Acta Physica Polonica A
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1992
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vol. 82
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issue 5
911-913
EN
We report optical absorption measurements of Fe-doped GaAs, InP and GaP crystals obtained with the help of different doping techniques. In all these crystals photoionization spectra corresponding to Fe^{3+} → Fe^{2+} transitions with sharp "excitonic" lines were observed. The intensities of these lines are not proportional to the intensities of photoionization absorption bands, i.e. to the concentration of the Fe^{3+} centers. Variation of more than one order of magnitude was observed for different semiconductors and for different crystals of the same material. These results suggest that only some iron centers are responsible for the "excitonic" spectra.
6
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Investigation of Quantum Dot Structures Grown by MOCVD in InAs/GaAs System

52%
Jasiński J., Bożek R., Stępniewski R., Kozubowski J.
Acta Physica Polonica A
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1998
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vol. 94
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issue 3
369-373
EN
Layers of InAs quantum dots grown on [100] GaAs substrates were characterised by photoluminescence and investigated by transmission electron microscopy. Two types of InAs islands were observed in these layers. The islands of the first type had mainly a form of big, elongated pyramids. Most of them were found to be dislocated. On the other hand, the islands of the second type were real self-assembled, coherent quantum dots giving rise to a characteristic photoluminescence band.
7
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Transmission Electron Microscopy and Luminescence Studies of Quantum Well Structures Resulting from Stacking Fault Formation in 4H-SiC Layers

46%
Borysiuk J., Wysmołek A., Bożek R., Strupiński W., Baranowski J.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1067-1072
EN
Transmission electron microscopy and photoluminescence studies of quantum well structures related to stacking faults formation in 4H-SiC homoepitaxial layers are reported. The investigated 4H-SiC layers were deposited on 8° misoriented Si-terminated (0001) surface of high quality 4H-SiC substrate. It is found that the planar defects created by direct continuation from the SiC substrates are cubic 3C-SiC stacking faults. These defects are optically active, giving rise to characteristic luminescence band in the spectral range around 2.9 eV, which consist of several emission lines. The observed energy and intensity pattern of this emission is discussed of in terms of single, double and multiple quantum wells formed from neighboring 3C-SiC SF layers embedded in 4H-SiC material.
8
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Infrared Optical and X-Ray Determination of Parameters for MOVPE Grown InAs_{1-x}Sb_{x} Epilayers

46%
Marszałek B., Zielińska-Rohozińska E., Bożek R., Stępniewski R., Witowski A.
Acta Physica Polonica A
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1997
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vol. 92
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issue 5
919-922
EN
The experimental room-temperature transmission of metalorganic vapour phase epitaxy grown InAsSb epilayers is compared with calculations based on a Kane model of the band structure. The band structure parameters are found. The composition of the samples was determined by X-ray diffraction.
9
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FIR Magnetooptical Measurements on MOCVD Grown InAs

46%
Andrearczyk T., Karpierz K., Bożek R., Stępniewski R., Grynberg M.
Acta Physica Polonica A
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1997
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vol. 92
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issue 4
699-703
EN
In this paper we report results of magnetooptical measurements done on standard InAs MOCVD layers grown on GaAs. Extremely narrow lines (half-widths of the order of 20 mT) - narrower than found by other authors in high quality MBE InAs epilayers on GaAs - as well as the lines of typical half-widths have been found both in the photoconductivity spectra and in the transmission spectra. A detailed comparison with the theoretical dependence of shallow donor and Landau level energies on magnetic field leads to the conclusion that they originate from cyclotron resonance and impurity-shifted cyclotron resonance transitions in that material.
10
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Tuning of Spectral Sensitivity of AlGaN/GaN UV Detector

39%
Korona K., Drabińska A., Trajnerowicz A., Bożek R., Pakuła K., Baranowski J.
Acta Physica Polonica A
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2003
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vol. 103
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issue 6
675-681
EN
GaN/AlGaN photodetector that exhibits new interesting property is presented. Its spectral sensitivity depends upon bias voltage. Under positive or low negative bias the detector is sensitive mainly to the ultrafiolet radiation absorbed by AlGaN layer 3.7-3.8 eV. Under negative bias U_B below -4 V, the detector is sensitive mainly to the radiation absorbed by GaN (3.4-3.6 eV). The effect can be explained based on numerical calculations of the electric field and potential profiles of this structure. The damping of GaN signal is attributed to activity of 2D electron gas formed on the GaN/AlGaN interface by spontaneous polarization. The reappearing of the signal is attributed to tunneling of holes through AlGaN, stimulated by a high electric field.
11
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Optical and Electrical Measurements of Low-Temperature InAlAs

39%
Korona K., Wysmołek A., Bożek R., Kamińska M., Baranowski J., Weber E.
Acta Physica Polonica A
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1992
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vol. 82
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issue 5
825-828
EN
Photoluminescence, photocurrent, thermally stimulated current and photoinduced current transient spectroscopy measurements done on molecular beam epitaxy In_{0.52}Al_{0.48}As layer, lattice matched to InP are reported. The investigated layers were grown on semi-insulating InP wafers, at temperature range from 215 to 450°C. It was found that the Fermi level was pinned to a dominant midgap center (most likely similar to EL2 center). Moreover, there were at least 7 other defects but with much smaller concentrations. Their activation energies were equal to 0.076, 0.11, 0.185, 0.295, 0.32 and 0.40 eV. The layers exhibited a very low luminescence and a small photocurrent.
12
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Optical and Electrical Studies of FR1 and FR2 Defects in GaAs

39%
Dwiliński R., Palczewska M., Kaczor P., Korona K., Wysmołek A., Bożek R., Kamińska M.
Acta Physica Polonica A
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1992
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vol. 82
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issue 4
613-616
EN
The systematic EPR, optical absorption, photoluminescence and thermally stimulated current studies of acceptor defects in bulk GaAs were performed. For the first time, parallel EPR and optical absorption experiments allowed to find the absorption spectrum due to the photoionization of FR1 defect with the threshold at 0.19 eV. Photoluminescence studies showed two families of bands in the energy range of about 1.25 to 1.35 eV. We tentatively ascribed them to FR1 and FR2 complexes with shallow donors. Thermally stimulated current measurements showed two peaks at 90 K and 110 K assigned to FR1 and FR2 respectively.
13
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Built-In Electric Field in High Quality GaN/AlGaN Quantum Wells

39%
Zieleniewski K., Pakuła K., Bożek R., Masztalerz K., Wysmołek A., Stępniewski R.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
657-659
EN
We report studies on electric field built in GaN/Al_{0.09}Ga_{0.91}N structure of nominally 6 nm wide quantum well. The sample was grown in horizontal metal-organic chemical vapor deposition reactor using innovative technology that decreases the density of screw dislocations. Firstly, using visible and mid infra-red interference pattern along the sample, the layer thickness and consequently the quantum well width was determined to vary linearly with the position. Secondly, photoluminescence spectra was taken at different positions. Correlation of those two measurements allows us to determine the built-in electric field to be 0.66 MV/cm, which is considerably larger than previously reported for similar structures.
14
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Temporal Evolution of Multi-Carrier Complexes in Single GaN/AlGaN Quantum Dots

39%
Surowiecka K., Wysmołek A., Stępniewski R., Bożek R., Pakuła K., Baranowski J.
Acta Physica Polonica A
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2005
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vol. 108
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issue 5
879-884
EN
Microphotoluminescence of low-density GaN/Al_xGa_{1-x}N quantum dots grown by metal-organic vapor phase epitaxy using in situ etching of AlGaN is presented. The narrow lines in the microphotoluminescence spectra due to the single quantum dots are observed. Both energy and intensity of these lines show temporal fluctuations. Statistical analysis based on the correlation matrix allowed us to identify objects, which are affected by photo-induced electric field fluctuations. Relations between emission lines participating in the spectrum are discussed.
15
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Content available

39%
Kwiatkowski A., Borysiuk J., Bożek R., Wasik D., Kamińska M., Sadowski J., Twardowski A.
Acta Physica Polonica A
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2006
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vol. 110
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issue 2
233-236
EN
We report on cross-sectional transmission electron microscopy and magnetic force microscopy studies performed on self-organized MnAs nanoclusters embedded in GaAs. It was found that 10÷20 nm large MnAs ferromagnetic nanocrystals were formed during rapid thermal annealing of Ga_{1-x}Mn_xAs layers at 600ºC, leading to magnetic contrasts in magnetic force microscopy images.
16
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Single GaN/AlGaN Quantum Dot Spectroscopy

39%
Surowiecka K., Wysmołek A., Stępniewski R., Bożek R., Pakuła K., Baranowski J.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
233-236
EN
Microphotoluminescence of low-density GaN/Al_{x}Ga_{1-x}N quantum dots grown by metal-organic vapor phase epitaxy using in situ etching of AlGaN is presented. The detailed analysis of the emission from these structures enables the observation of pairs of lines separated by the energy up to 3 meV. They behave in a different way under different excitation power that suggests that this doublet structure can be associated with the exciton and trion (or biexciton recombination). It is observed that for different quantum dots the energy of the charged exciton complex emission could be higher or lower than the neutral exciton one. It is discussed in terms of a competition between attractive e-h and repulsive e-e (h-h) Coulomb interaction that occurs because of the existence of the built-in electric field that separates electrons and holes in the dot.
17
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Raman Studies of Defects in Graphene Grown on SiC

39%
Grodecki K., Bożek R., Borysiuk J., Strupinski W., Wysmolek A., Stępniewski R., Baranowski J.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
595-596
EN
The Raman scattering studies of multi-layer graphene obtained by high temperature annealing of carbon terminated face of 4H-SiC(000-1) substrates are presented. Intensity ratio of the D and G bands was used to estimate the average size of the graphene flakes constituting carbon structures. The obtained estimates were compared with flake sizes from atomic force microscopy data. We found that even the smallest structures observed by atomic force microscopy images are much bigger than the estimates obtained from the Raman scattering data. The obtained results are discussed in terms of different average flake sizes inside and on the surface of the multi-layer graphene structure, as well as different type of defects which would be present in the investigated structures apart from edge defects.
18
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Light Induced Modification of Graphene Oxide Layers on GaN Basis

39%
Łopion A., Stobiński L., Pakuła K., Bożek R., Kaźmierczak P., Wysmołek A., Stępniewski R.
Acta Physica Polonica A
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2016
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vol. 130
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issue 5
1169-1171
EN
Graphene oxide suspension in various solvents was spin coated on metal organic vapor phase epitaxy grown GaN/saphire layers. Samples were characterised using the Raman spectroscopy and atomic force microscopy, before and after high temperature treatment. We found that graphene oxide was modifed by high temperature treatment, however a considerable modification was also observed as a result of impinged laser light incident due to the measurements. The Raman spectra were decomposed into two contributions showing different behaviour during the Raman scattering measurements.
19
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Highly Compensated GaAs Crystal Obtained by Molecular CO Doping

39%
Bożek R., Korona K., Nowak G., Wasik D., Słupiński T., Kaczor P.
Acta Physica Polonica A
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1993
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vol. 84
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issue 4
669-672
EN
GaAs:C crystal was grown by liquid encapsulated Czochralski technique with large partial pressure of CO in ambient atmosphere p_{CO}/p_{tot} = 0.2 and investigated using near and infrared absorption, photoluminescence, photoconductivity, photo-induced current transient spectroscopy and photo-Hall measurements. High resistivity of the crystal was found in electrical measurements (10^{7} Ω cm, the Fermi level at 0.67 eV below conduction band at 300 K). Local vibrational mode revealed increased concentration of carbon acceptor and presence of oxygen related complexes. Photoluminescence spectra were dominated by two bands with peak energies at 1.49 eV and 0.8 eV. The near band gap emission shifts with excitation intensity up to 4 meV/decade. In photocurrent spectrum a strong photoionization band with E = 0.55 eV is observed.
20
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Time Evolution of the Microluminescence Energy οf GaN/AlGaN Quantum Dots

39%
Surowiecka K., Wysmołek A., Stępniewski R., Bożek R., Pakuła K., Baranowski J.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
933-935
EN
Time evolution of the microphotoluminescence from low-density GaN/Al_{x}Ga_{1-x}N quantum dots grown by metal organic chemical vapor deposition using in situ etching of AlGaN is presented. The observed effect is related to the energy changes that begin immediately after sample illumination with the exciting laser light and saturate after some time. Typically, the luminescence energy decreases and the change is exponential with characteristic times in a range between several dozen and several hundred seconds. However, sometimes we observed the energy increase with characteristic times in a range between several and a few hundred seconds. The obtained results are discussed in terms of the metastable change of the electric field, induced by spontaneous polarization present in GaN/AlGaN structure (in the growth direction), and strain- or defect-induced changes of the electric field in the vicinity of the dot.
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