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1
Content available remote

Optical Properties of Molecular Beam Epitaxy Grown ZnSe on GaAs

100%
Karpińska K., Suchocki A., Godlewski M., Hommel D.
Acta Physica Polonica A
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1993
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vol. 84
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issue 3
551-554
EN
Photoluminescence studies of molecular beam epitaxy grown ZnSe-on-GaAs layers are presented. The high sensitivity of the PL technique allowed for identification unintentional dopants in pure ZnSe sample. Characteristic photoluminescence lines due to extended defects were observed. The experimental results obtained show a correlation between intentional doping level and extended defects concentration. We conclude also that even though molecular beam epitaxy layers are grown at low temperature, the self-compensation mechanism may still be important. For heavily doped sample edge emission is deactivated likely due to efficient energy transfer link with deep donor-acceptor pair bands.
2
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Determination of the Temperature Dependent Thermal Expansion Coefficients of Bulk AlN by HRXRD

100%
Kröncke H., Figge S., Hommel D., Epelbaum B.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1193-1200
EN
We measured the lattice constants of bulk aluminum nitride crystals at various temperatures by high resolution X-ray diffraction. By the use of a high temperature chamber and a X-ray cryostat a temperature regime from 20 to 1210 K was available. Furthermore, the measured data were fitted by Einstein- and Debye models which yield reliable parameters for the calculation of the thermal expansion coefficients of AlN.
3
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Enhanced Exciton-Phonon Interaction in Strained ZnCdSe/ZnSe Quantum Well Structures

100%
Godlewski M., Leonardi K., Hommel D.
Acta Physica Polonica A
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1997
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vol. 92
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issue 4
769-773
EN
Radiative recombination processes in pseudomorphic ZnCdSe/ZnSe structures are compared to those observed in strain-relaxed structures grown on GaAs substrates with thick ZnSe buffer layers. From the temperature dependence of the photoluminescence line width we evaluate the strength of exciton-phonon interaction with acoustic (dominant at lower temperatures) and optical phonons. Stronger exciton-phonon interaction is observed for pseudomorphic structures. Such enhanced exciton-phonon interaction is likely responsible for a faster photoluminescence deactivation at increased temperatures. We also report different exciton properties (photoluminescence intensity, width, strength of exciton-phonon interaction) in quantum well of a given width but in structures grown with different order of quantum wells. More stable photoluminescence (with increasing temperature) is observed for a given quantum well if it is closer to the buffer layer and not to the cap layer.
4
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Influence of Growth Conditions on Optical Properties of ZnCdSe/ZnSe Quantum Wells Grown by Molecular Beam Epitaxy

88%
Godlewski M., Bergman J., Monemar B., Kurtz E., Hommel D.
Acta Physica Polonica A
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1996
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vol. 90
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issue 4
785-788
EN
The results of investigations of photoluminescence, time-resolved photoluminescence, photoluminescence kinetics and their temperature dependencies are discussed for two types of ZnCdSe/ZnSe multi quantum well structures - for pseudomorphic and for strain relaxed structure. Densities of 2D localized states and averaged localization energies, as seen by excitons, are determined from the photoluminescence kinetics measurements. We show distinct differences between exciton properties in two multi quantum well structures studied.
5
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Characterization of n-ZnO/p-GaN Heterojunction for Optoelectronic Applications

76%
Wachnicki L., Gieraltowska S., Witkowski B., Figge S., Hommel D., Guziewicz E., Godlewski M.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
869-872
EN
An important feature of zinc oxide and gallium nitride materials are their similar physical properties. This allows to use them as a p-n junction materials for applications in optoelectronics. In earlier work we presented use of ZnO as a transparent contact to GaN, which may improve external efficiency of LED devices. In this work we discuss properties of a n-ZnO/p-GaN heterostructure and discuss its optimization. The heterostructure is investigated by us for possible applications, e.g. in a new generation of UV LEDs or UV light detectors.
6
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Comparison of Exciton Properties in Quantum Well Structures of ZnCdSe/ZnSe and ZnSe/ZnMgSSe

76%
Godlewski M., Ivanov V., Bergman J., Monemar B., Leonardi K., Behringer M., Hommel D.
Acta Physica Polonica A
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1998
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vol. 94
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issue 2
313-316
EN
Properties of excitons in quantum well structures of ZnCdSe/ZnSe and ZnSe/ZnMgSSe are compared. In ternary ZnCdSe quantum wells and at low temperature excitons are strongly localised. Weaker localization is observed in quantum well structures of ZnSe/ZnMgSSe. Present studies suggest formation of negatively charged excitons in the latter structures.
7
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Optical Characterization of CdZnSe/ZnSe Multiquantum Well System

76%
Godlewski M., Karpińska K., Bergman J., Monemar B., Kurtz E., Hommel D.
Acta Physica Polonica A
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1995
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vol. 87
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issue 1
209-212
EN
Optical properties of Cd_{x}Zn_{1-x}Se/ZnSe (x = 0.12) multiquantum well system are discussed. The transient photoluminescence and optically de­tected cyclotron resonance experiments demonstrate a strong contribution of bound exciton emission to the low temperature photoluminescence spec­tra.
8
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Comparison of Long-Time Delay in Lasing in Homo- and Heteroepitaxially Grown II-VI Laser Diodes

76%
Isemann A., Behringer M., Wenisch H., Fehrer M., Ohkawa K., Hommel D.
Acta Physica Polonica A
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1998
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vol. 94
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issue 2
355-358
EN
Gain guided laser diodes exhibit unexpected low threshold current densities. Under these conditions, lasing only occurs under a current dependent long-time delay, which is three orders of magnitude larger than the time needed to reach population inversion. This effect is attributed to a thermally induced index guiding. The change in temperature of the quantum well region can be estimated using the shift in the wavelength of emission to be up to 70 K. As a further consequence, the threshold current density can be reduced by a factor of 4 simply by changing the pulse width of the applied current.
9
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Toward Better Light-Confinement in Micropillar Cavities

64%
Ściesiek M., Gietka K., Golnik A., Kossacki P., Jakubczyk T., Pacuski W., Kruse C., Hommel D.
Acta Physica Polonica A
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2011
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vol. 120
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issue 5
877-879
EN
We report on a two-step etching of ZnTe based micropillars. We demonstrate applicability of the technology and we analyze the optical properties of obtained structures. Microphotoluminescence spectra of individual micropillars show a typical mode pattern that confirms a successful growth of photonic structures. The reflectivity and photoluminescence spectra of a planar microcavity measured for various incident angles show that additional side distributed Bragg reflectors will be important for the further enhancement of photon confinement in micropillar cavity.
10
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Optical Properties of CdTe QDs Formed Using Zn Induced Reorganization

64%
Kobak J., Pacuski W., Jakubczyk T., Kazimierczuk T., Golnik A., Frank K., Rosenauer A., Kruse C., Hommel D., Gaj J.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
627-629
EN
In this paper we present optical studies of CdTe quantum dots formed using Zn-induced reorganization. The pattern of quantum dot photoluminescence lines is found to be similar to typical results reported for quantum dots grown with other techniques, although the positively charged exciton line is relatively more pronounced. Also the energy spacing between biexciton and exciton lines is found to be larger than in typical results. Zn-induced reorganization results in quantum dots density higher by an order of magnitude than in Te-induced quantum dots.
11
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Deep Levels Induced by CdTe/ZnTe Quantum Dots

64%
Zielony E., Placzek-Popko E., Roznicka A., Gumienny Z., Szatkowski J., Dyba P., Pacuski W., Kruse C., Hommel D., Guziewicz M.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
630-632
EN
The electrical properties of the CdTe/ZnTe quantum dot system have been analyzed to identify deep-level defects related with the presence of quantum dots. The capacitance-voltage (C-V) and deep level transient spectroscopy measurements were used to investigate the samples. A reference ZnTe sample (without dots) was also studied for comparison. Both samples were grown by molecular beam epitaxy technique on the n-type GaAs substrate. The quantum dots were formed by a Zn-induced reorganization of a thin CdTe layer. The presence of quantum dot formation was confirmed by micro-photoluminescence measurements. The deep level transient spectra for both samples are complex. In order to characterize individual contributions to the deep level transient spectra the latter have been simulated by separated Gaussian components [1]. The results of the deep level transient spectroscopy measurements yield the conclusion that the same defects are present in both materials but there is an increased concentration of the defects in the quantum dot structures. No deep level associated directly with the quantum dot confinement has been identified.
12
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Optical Study of ZnTe-Based 2D and 0D Photonic Structures Containing CdTe/ZnTe Quantum Dots

64%
Jakubczyk T., Kazimierczuk T., Golnik A., Bienias P., Pacuski W., Kruse C., Hommel D., Kłopotowski Ł., Wojtowicz T., Gaj J.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
888-889
EN
We report on an optical study of ZnTe-based microcavity and micropillars. Angle-resolved reflectivity studies confirm a high quality of the investigated structure by setting the lower bound on the quality factor Q ≥ 1000, determined from normal-incidence reflection spectra. In a microphotoluminescence study, micropillar modes are observed at temperatures of the order of tens of kelvins. For structures grown by a complex growth procedure at two different MBE facilities, an enhancement of photoluminescence in the cavity mode is observed.
13
Publication available in full text mode
Content available

Light Emission Properties of GaN-Based Laser Diode Structures

64%
Godlewski M., Phillips M., Czernecki R., Targowski G., Perlin P., Leszczyński M., Figge S., Hommel D.
Acta Physica Polonica A
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2005
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vol. 108
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issue 4
675-680
EN
Cathodoluminescence is applied for evaluation of in-depth and in-plane variations of light emission from two types of GaN-based laser diode structures. We evaluate in-depth properties of the laser diode emission and demonstrate that potential fluctuations still affect emission of laser diodes for e-beam currents above thresholds for a stimulated emission.
14
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Epitaxial ZnO Films Grown at Low Temperature for Novel Electronic Application

52%
Wachnicki Ł., Dużyńska A., Domagala J., Witkowski B., Krajewski T., Przeździecka E., Guziewicz M., Wierzbicka A., Kopalko K., Figge S., Hommel D., Godlewski M., Guziewicz E.
Acta Physica Polonica A
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2011
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vol. 120
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issue 6A
A-7-A-10
EN
Monocrystalline films of zinc oxide were grown at 300C by atomic layer deposition. ZnO layers were grown on various substrates like ZnO bulk crystal, GaN, SiC and Al_2O_3. Electrical properties of the films depend on structural quality. Structural quality, surface morphology and optical properties of ZnO films were characterized using X-ray diffraction, scanning electron microscopy, and photoluminescence, respectively. High resolution X-ray diffraction spectra show that the rocking curve FWHM of the symmetrical 00.2 reflection equals to 0.058° and 0.009° for ZnO deposited on a gallium nitride template and a zinc oxide substrate, respectively. In low temperature photoluminescence sharp excitonic lines in the band-edge region with a FWHM equal to 4 meV, 5 meV and 6 meV, for zinc oxide deposited on gallium nitride, zinc oxide and sapphire substrate, respectively.
15
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Cathodoluminescence Profiling of InGaN-Based Quantum Well Structures and Laser Diodes - In-Plane Instabilities of Light Emission

52%
Godlewski M., Ivanov V., Goldys E., Phillips M., Böttcher T., Figge S., Hommel D., Czernecki R., Prystawko P., Leszczynski M., Perlin P., Grzegory I., Porowski S.
Acta Physica Polonica A
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2003
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vol. 103
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issue 6
689-694
EN
Instabilities of light emission and also of stimulated emission in series of GaN epilayers and InGaN quantum well structures, including laser diode structures, are studied. A stimulated emission is observed under electron beam pumping. This enabled us to study light emission properties from laser structures and their relation to microstructure details. We demonstrate large in-plane fluctuations of light emission and that these fluctuations are also present for excitation densities larger than the threshold densities for the stimulated emission.
16
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Optical Properties and Microstructure of InGaN Grown by Molecular Beam Epitaxy

52%
Böttcher T., Einfeldt S., Figge S., Kirchner V., Hommel D., Selke H., Ryder P., Bertram F., Riemann T., Christen J., Lunz U., Becker C.
Acta Physica Polonica A
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1998
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vol. 94
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issue 2
260-264
EN
The luminescence of In_{x}Ga_{1-x}N is studied for thick epitaxial layers and quantum wells. Using spatially resolved cathodoluminescence spectroscopy the commonly observed broad integral photoluminescence spectra were found to result from spectral and lateral inhomogeneous emission across the samples. Moreover, the integral photoluminescence and absorption spectra show different temperature dependences. The effects can be explained assuming fluctuations of the composition associated with a variation of the band gap.
17
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Content available

Microwave-Induced Delocalization of Excitons in Ternary Compounds of II-VI and III-V Semiconductors

52%
Ivanov V., Godlewski M., Khachapuridze A., Yatsunenko S., Wojtowicz T., Karczewski G., Bergman J., Monemar B., Shamirzaev T., Zhuravlev K., Leonardi K., Hommel D.
Acta Physica Polonica A
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2003
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vol. 103
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issue 6
559-566
EN
In this work we employ technique of optically detected cyclotron resonance for evaluation of the role of localization processes in CdTe/CdMnTe and CdMnTe/CdMgTe quantum well structures. From microwave-induced changes of excitonic emissions we evaluate magnitude of potential fluctuations (Stokes shift), correlate optically detected cyclotron resonance results with the results of time-resolved experiments and discuss nature of recombination processes in the limit of a strong localization.
18
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Content available

Relationship between Sample Morphology and Carrier Diffusion Length in GaN Thin Films

52%
Godlewski M., Goldys E., Phillips M., Böttcher T., Figge S., Hommel D., Czernecki R., Prystawko P., Leszczynski M., Perlin P., Wisniewski P., Suski T., Bockowski M., Grzegory I., Porowski S.
|
|
issue 4-5
627-632
EN
Scanning and spot-mode cathodoluminescence investigations of homo- and hetero-epitaxial GaN films indicate a surprisingly small influence of their microstructure on overall intensity of a light emission. This we explain by a correlation between structural quality of these films and diffusion length of free carriers and excitons. Diffusion length increases with improving structural quality of the samples, which, in turn, enhances the rate of nonradiative recombination on structural defects, such as dislocations.
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