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1
Content available Multiband GaN/AlGaN UV Photodetector
100%
Korona K. , Drabińska A. , Pakuła K. , Baranowski J.
Acta Physica Polonica A
|
2006
|
tom 110
|
nr 2
211-217
EN
We present optical and electrical measurements made on GaN/AlGaN photodetector structure capable to detect three UV ranges, tuned by external voltage. The highest band at energy of about 3.85 eV is nearly independent of bias applied to the Schottky contact. Photosensitivity of the second band at about 3.65 eV changes strongly with the bias. Signal in this range increases about 20 times when the bias changes from 0 V to -4 V. Photosensitivity of the third band (3.4 eV) appears for strong reverse bias (-3 V). Characteristics of the detector are in qualitative agreement with numerical model, however deep centers present in the AlGaN layers cause quantitative discrepancies. The concentration of defects of the order of 10^{16} cm^{-3} was estimated from current transients.
2
Content available An Estimate of the Energy Gap of InN from Measurements of the Fundamental Absorption Edge
100%
Trautman P. , Pakuła K. , Witowski A. , Baranowski J.
Acta Physica Polonica A
|
2005
|
tom 108
|
nr 5
903-908
EN
Optical absorption between 0.4 and 4.5 eV of an InN layer grown by metalorganic vapour phase epitaxy on sapphire was measured at 296 and 12 K. The layer was also characterized by measurements of the Hall effect and of infrared reflectivity in the region of the plasma edge, which determined the concentration, mobility, and effective mass of electrons in the conduction band. The energy gap of InN was estimated to be equal to 0.9±0.2 eV. It was obtained from the spectral position of the fundamental absorption edge. Corrections to the energy gap resulting from the broadening of the fundamental absorption edge, from the Burstein-Moss shift, and from a band-gap shrinkage due to the impurity potential were included.
3
Content available remote Deep Level Transient Spectroscopic Studies of MOCVD GaN Layers Grown on Sapphire
100%
Śliwiński A. , Korona K. , Pakuła K. , Baranowski J.
Acta Physica Polonica A
|
1996
|
tom 90
|
nr 5
955-958
EN
The deep level transient spectroscopy of GaN heteroepitaxial layers grown on sapphire was studied. The samples were Mg doped during the growth. The as-grown material is n-type. It becomes p-type after annealing. The samples were measured in the temperature range from 77 K to 420 K. In n-type GaN, one peak (EG1) with activation energy 0.75 eV was detected. In p-type, at least three peaks were observed: AS1 at temperature about 300 K and AS2, AS3 at about 400 K. The dominating one is AS3. It has an activation energy about 1.1 eV.
4
Content available remote s,p-d Exchange Constants of CdFeSe Semimagnetic Semiconductor
100%
Arciszewska M. , Pakuła K. , Perez I. , Twardowski A.
Acta Physica Polonica A
|
1991
|
tom 79
|
nr 2-3
345-348
EN
We report determination of s, p-d exchange constants for hexagonal CdFeSe combining exciton splitting and magnetization measurements performed on the same samples.
5
Content available remote Electrical and ESR Studies of GaN Layers Grown by Metal Organic Chemical Vapour Deposition
88%
Suchanek B. , Palczewska M. , Pakuła K. , Baranowski J. , Kamińska M.
Acta Physica Polonica A
|
1997
|
tom 92
|
nr 5
1001-1004
EN
Electrical transport and ESR studies were performed on the state-of-theart GaN layers grown on sapphire substrate using metal organic chemical vapour deposition technique. For undoped samples electron concentration below 2×10^{17} cm^{-1} and mobility up to 500 cm^{2}/(V s) were achieved whereas hole concentration up to 7×10^{17} cm^{-3} and mobility about 16 cm^{2}/(V s) were obtained for intentionally Mg doped samples and subsequently annealed. Temperature dependence of mobility was discussed. ESR revealed the presence of two resonance absorption lines. One of them with g_{⊥}=1.9487 and g_{∥}=1.9515, commonly observed in n-type GaN was due to shallow donor. The second ESR line was an isotropic one of g=2.0032 and it is discussed.
6
Content available Tuning of Spectral Sensitivity of AlGaN/GaN UV Detector
75%
Korona K. , Drabińska A. , Trajnerowicz A. , Bożek R. , Pakuła K. , Baranowski J.
Acta Physica Polonica A
|
2003
|
tom 103
|
nr 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.
7
Content available remote Two-Electron Transition in Homoepitaxial GaN Layers
75%
Fiorek A. , Baranowski J. , Wysmołek A. , Pakuła K. , Wojdak M. , Grzegory I. , Porowski S.
Acta Physica Polonica A
|
1997
|
tom 92
|
nr 4
742-744
EN
It is shown that the luminescence mapping is a powerful method to help identify optical transitions. Two-electron transition was identified in the homoepitaxial GaN layer by this technique. It was found that the donor and acceptor bound exciton emissions are spatially displaced and show intensity maxima at different places of the epitaxial layer. It was also found that the 3.45 eV line, suspected as "two-electron transition", follows exactly the donor bound exciton spatial distribution. Donor bound exciton recombines leaving the neutral donor in the excited 2s state. Thus, 1s-2s excitation being equal to 22 meV corresponds to 29 meV hydrogenic donor binding energy. This is the first identification of the two-electron transition in GaN.
8
Content available remote Single GaN/AlGaN Quantum Dot Spectroscopy
75%
Surowiecka K. , Wysmołek A. , Stępniewski R. , Bożek R. , Pakuła K. , Baranowski J.
Acta Physica Polonica A
|
2007
|
tom 112
|
nr 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.
9
Content available remote Built-In Electric Field in High Quality GaN/AlGaN Quantum Wells
75%
Zieleniewski K. , Pakuła K. , Bożek R. , Masztalerz K. , Wysmołek A. , Stępniewski R.
Acta Physica Polonica A
|
2011
|
tom 119
|
nr 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.
10
Content available remote Time Evolution of the Microluminescence Energy οf GaN/AlGaN Quantum Dots
75%
Surowiecka K. , Wysmołek A. , Stępniewski R. , Bożek R. , Pakuła K. , Baranowski J.
Acta Physica Polonica A
|
2009
|
tom 116
|
nr 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.
11
Content available remote Optical and Electrical Properties of High Temperature Annealed Heteroepitaxial GaN:Mg Layers
75%
Wojdak M. , Baranowski J. M. , Suchanek B. , Pakuła K. , Jun J. , Suski T.
Acta Physica Polonica A
|
1997
|
tom 92
|
nr 5
1059-1062
EN
In this paper we present for the first time luminescence and electrical measurements of GaN:Mg heteroepitaxial layers annealed at very high temperatures up to 1500°C and at high pressures of nitrogen up to 16 kbar. The presence of high nitrogen pressure prevents GaN from thermal decomposition. It was found that annealing in the presence of additional Mg atmosphere leads to a high quality p-type epitaxial layer of the hole concentration equal to 2×10^{17} cm^{-3} and mobility 16 cm^{2}/(V s). However, annealing at high temperatures without additional magnesium causes conversion to n-type. It is also shown that in the high temperature annealed GaN:Mg epilayers the donor-acceptor luminescence is the dominant recombination channel.
12
Content available remote Luminescence Dynamics of Exciton Replicas in Homoepitaxial GaN Layers
75%
Korona K. , Baranowski J. , Pakuła K. , Monemar B. , Bergman J. , Grzegory I. , Porowski S.
Acta Physica Polonica A
|
1997
|
tom 92
|
nr 4
841-844
EN
Photoluminescence of excitons and their phonon replicas in homoepitaxial MOCVD-grown gallium nitride (GaN) layers have been studied by picosecond (ps) time-resolved photoluminescence spectroscopy. The time-resolved photoluminescence spectroscopy has shown that the free excitons and their replicas have the fastest dynamics (decay time of about 100 ps). Then, the excitons-bound-to-donors emission rises (with the rise time similar to the free excitons decay time) and decays with t=300 ps. The excitons-bound-to-acceptors has the slowest decay (about 500 ps). It has been found that the ratio of excitons-bound-to-acceptors and excitons-bound-to-donors amplitudes and their decay times are different for 1-LO replicas and then for zero-phonon lines, whereas the ratio of amplitudes and the decay time of the 2-LO replicas are similar to the ones of the zero-phonon lines.
13
Content available Temporal Evolution of Multi-Carrier Complexes in Single GaN/AlGaN Quantum Dots
75%
Surowiecka K. , Wysmołek A. , Stępniewski R. , Bożek R. , Pakuła K. , Baranowski J.
Acta Physica Polonica A
|
2005
|
tom 108
|
nr 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.
14
Content available remote Light Induced Modification of Graphene Oxide Layers on GaN Basis
75%
Łopion A. , Stobiński L. , Pakuła K. , Bożek R. , Kaźmierczak P. , Wysmołek A. , Stępniewski R.
Acta Physica Polonica A
|
2016
|
tom 130
|
nr 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.
15
Content available remote Optical and Electrical Studies of Graphene Deposited on GaN Nanowires
63%
Kierdaszuk J. , Kaźmierczak P. , Drabińska A. , Wysmołek A. , Korona K. , Kamińska M. , Pakuła K. , Pasternak I. , Krajewska A. , Żytkiewicz Z.
Acta Physica Polonica A
|
2014
|
tom 126
|
nr 5
1087-1089
EN
In this paper using scanning electron microscope, contactless microwave electronic transport and the Raman spectroscopy we studied the properties of graphene deposited on GaN nanowires and compared it with the graphene deposited on GaN epilayer. The Raman micro-mapping showed that nanowires locally change the strain and the concentration of carriers in graphene. Additionally we observed that nanowires increase the intensity of the Raman spectra by more than one order of magnitude.
16
Content available remote Coupling of LO Phonons to Excitons in GaN
63%
Wysmołek A. , Łomiak P. , Baranowski J. , Pakuła K. , Stępniewski R. , Korona K. , Grzegory I. , Boćkowski M. , Porowski S.
Acta Physica Polonica A
|
1996
|
tom 90
|
nr 5
981-984
EN
The photoluminescence of homoepitaxial and heteroepitaxial GaN layers is reported. It is shown that the coupling between LO phonons and neutral acceptor bound excitons is much stronger than the coupling between LO phonons and neutral donor bound excitons. In undoped homoepitaxial layer, in spite of that the no-phonon emission due to donor bound excitons is one order of magnitude stronger than the acceptor bound excitons emission, the predominant structure in the LO phonon replica of the excitonic spectrum is related to optical transitions involving acceptor bound excitons. Temperature studies showed that at higher temperature the LO phonon replica is related to free excitons.
17
Content available Spatially Resolved Micro-Luminescence from GaN/AlGaN Quantum Dots
63%
Chwalisz B. , Wysmołek A. , Bożek R. , Stępniewski R. , Pakuła K. , Kossacki P. , Golnik A. , Baranowski J.
Acta Physica Polonica A
|
2004
|
tom 105
|
nr 6
517-521
EN
We report on the optical experiments performed on low density GaN/AlGaN quantum dots grown on sapphire substrate using SiN during the growth process. The existence of quantum dots in the investigated structures was confirmed by atomic force microscopy. Although macro-luminescence of the investigated structures consist of broad emission lines the micro-photoluminescence experiments performed with the spatial resolution of 0.25 μm revealed sharp emission lines from the individual quantum dot in the energy range of 3.20-3.55 eV. It is shown that the magnetic fields up to 7 T do not influence significantly the electronic states of the dots.
18
Content available Potential and Carrier Distribution in AlGaN Superlattice
63%
Korona K. , Pakuła K. , Bożek R. , Drabińska A. , Surowiecka K. , Stępniewski R. , Zielińska-Rohozińska E. , Baranowski J.
Acta Physica Polonica A
|
2005
|
tom 108
|
nr 4
723-729
EN
Photocurrent spectroscopy and Kelvin force microscopy have been used in order to determine charge, field, and potential distributions in spontaneously grown superlattice. The spectra show that light can generate currents and potentials in both directions depending on photon energy. A numerical model made for superlattice of periodλ_{SL} = 33 nm shows that electric field in superlattice oscillates coherently with Al content. The oscillations of electric field explain the different directions of photocurrent. The electric field can also separate electrons and holes, making carrier lifetimes longer and lowering excitation intensity threshold for occupation inversion.
19
Content available remote Structural and Optical Properties of Boron Nitride Grown by MOVPE
63%
Dąbrowska A. , Pakuła K. , Bożek R. , Rousset J. , Ziółkowska D. , Gołasa K. , Korona K. , Wysmołek A. , Stępniewski R.
Acta Physica Polonica A
|
2016
|
tom 129
|
nr 1a
A-129-A-131
EN
Boron nitride layers were grown on sapphire substrate by metal organic vapor phase epitaxy system that was originally designed for growth of GaN. Structures were characterized by scanning electron microscopy, atomic force microscopy, the Raman spectroscopy, absorption and time resolved photoluminescence. Presented results confirm successful deposition of BN layers and gives information about basic properties of the material. The Raman line at 1370 cm^{-1} and absorption edges at 5.6-5.9 eV were observed which is related to hexagonal phase.
20
Content available Localization Effects in GaN/AlGaN Quantum Well - Photoluminescence Studies
51%
Chwalisz B. , Wysmołek A. , Bożek R. , Korona K. , Stępniewski R. , Knap W. , Pakuła K. , Baranowski J. , Grandjean N. , Massies J. , Prystawko P. , Grzegory I.
Acta Physica Polonica A
|
2003
|
tom 103
|
nr 6
573-578
EN
Exciton localization in GaN/AlGaN quantum well structures is studied by photoluminescence. An anomalous temperature behavior of the photoluminescence from the quantum well is observed. With increasing temperature the energy position of the excitonic emission line first decreases up to 20 K, then increases, reaching a maximum around 90 K, and then decreases again in the higher temperature range. The observed behavior is discussed in terms of localization at the interface potential fluctuations. It is argued that the temperature activated migration and subsequent release of the excitons from traps that occurs between 20 K and 90 K are responsible for the observed S-like shape of the energy dependence. The obtained results allow a direct characterization of the energy fluctuations present in GaN/AlGaN quantum wells grown by different techniques.
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