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1
Content available Dynamics of Excitation Transfer Inside InAs/GaAs Quantum Dot System
100%
Korona K. , Babiński A. , Raymond S. , Wasilewski Z.
Acta Physica Polonica A
|
2006
|
tom 110
|
nr 2
219-224
EN
We present time-resolved photoluminescence investigations of InAs/GaAs structures containing quantum dots with the ground state at 1.43 eV. State filling effect and a Pauli blocking effect were clearly observed. These effects significantly influenced dynamics of excitation transfer from upper to lower state inside a dot leading to non-exponential dynamics. Numerical model based on nonlinear rate equations was proposed. The model described well the experimental data providing values of: lifetime of the ground state 0.53±0.03 ns, lifetime of excited state (when the ground state is full) 1.1±0.2 ns, and internal relaxation time (when the ground state is empty) 0.07±0.01 ns.
2
Content available remote Influence of Electric Field on Recombination Dynamics of Quantum Confined Carriers
100%
Korona K. , Borysiuk J. , Skierbiszewski C. , Porowski S.
Acta Physica Polonica A
|
2007
|
tom 112
|
nr 2
243-247
EN
We present time-resolved photoluminescence measurements of GaN/AlGaN low dimensional structures showing very characteristic changes of dynamics related to strong electric field. Strong piezoelectric and spontaneous polarizations built-in in nitride structures lead to the changes in spatial separation of carriers which leads to changes in recombination energies and radiative lifetimes of the carriers. The observed effect can be well described by a simple exponential relation. The observed dependence can be explained by an approximated model of quantum-confined Stark effect based on the Airy functions.
3
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.
4
Content available remote Transport of Photoexcited Electron-Hole Plasma in GaN/AlGaN Quantum Well
100%
Korona K. , Caban P. , Strupiński W.
Acta Physica Polonica A
|
2009
|
tom 116
|
nr 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.
5
Content available remote Deep Defects in Low-Temperature GaAs
100%
Korona K. , Muszalski J. , Kamińska M. , Weber E.
Acta Physica Polonica A
|
1992
|
tom 82
|
nr 5
821-824
EN
Conductivity of GaAs layers grown by molecular beam epitaxy at low substrate temperature (190-200°C) and then annealed at few different temperatures (between 300 and 600°C) were studied. It was confirmed that electron transport is due to hopping between arsenic antisite defects. Parameters describing hopping conductivity and their dependence on temperature of annealing are discussed. Other deep defects with activation energies of 0.105, 0.30, 0.31, 0.47, 0.55 eV were found using photoinduced current transient spectroscopy measurements.
6
Content available remote Efficient Emission from InAlGaAs Single Quantum Dots with Low Lattice Misfit and AlGaAs Indirect Bandgap Barrier
100%
Słupiński T. , Korona K. , Papierska J. , Borysiuk J.
Acta Physica Polonica A
|
2016
|
tom 130
|
nr 5
1229-1232
EN
We report on molecular beam epitaxy growth and properties of rarely studied quaternary In_{0.4}(Al_{0.75}Ga_{0.25})_{0.6}As self-assembled quantum dots, which show strong and efficient emission of red light from single quantum dots. The increased yield is, among others, due to efficient energy transfer from indirect band-gap Al_{0.75}Ga_{0.25}As barriers. To maximize photon energy emitted from quantum dots, low In composition, x_{In} = 0.4 was applied, which also lowered the lattice misfit close to the limit of 2D/3D transition in the Stranski-Krastanov growth mode. Time-resolved micro-photoluminescence shows emission at 650-750 nm. Well-resolved single quantum dot photoluminescence lines (decay time of ≈ 1-2 ns) are observed despite a high concentration ≈ 3×10¹¹ cm¯² of quantum dots. We discuss this observation assuming newly a role of carriers or excitons diffusion/tunneling between quantum dots at high surface concentration of dots and a possible role of lattice disorder inside the dot on the exciton lifetime.
7
Content available remote Photoreflectance Measurements of InGaAs/GaAs Quantum Wells
100%
Tomaszewicz T. , Korona K. , Bożek R. , Baranowski J.
Acta Physica Polonica A
|
1996
|
tom 90
|
nr 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.
8
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.
9
Content available remote Model of Hopping between Deep Centers in Low Temperature GaAs
100%
Korona K. , Kamińska M. , Baranowski J.
Acta Physica Polonica A
|
1995
|
tom 87
|
nr 2
337-340
EN
A model explaining hopping conductivity via EL2 deep centers in low temperature GaAs is presented. It is proposed that the wave function of the EL2 center consists of a localized part and of an external one. The model can describe such features as large wave function radius of hopping centers, changes of the conductivity during transition of EL2 to the metastable state and a high potential fluctuation amplitude.
10
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.
11
Content available remote Anharmonic Optical Phonon Effects in ZnO Nanocrystals
75%
Khusnutdinov S. , Dynowska E. , Zaleszczyk W. , Makhniy V. , Wysmołek A. , Korona K.
Acta Physica Polonica A
|
2011
|
tom 119
|
nr 5
678-680
EN
Zinc oxide (ZnO) is a very promising material for optoelectrical devices operating at the short-wavelength end of the visible spectral range and at the near UV. The Raman scattering studies of ZnO heterolayers formed by isothermal annealing show sharp phonon lines. In addition to the A_1(TO), E_1(TO), E_2^{H}, and E_1(LO) one-phonon lines, we observed two-phonon lines identified as: E_2^{H} - E_2^{L}, E_2^{H} + E_2^{L}, and 2LO at 332, 541, and 1160 cm^{-1}, respectively (at room temperature). The identification of the E_2^{H} - E_2^{L} peak was confirmed by its thermal dependence. Temperature dependent measurements in the range 6-300 K show that the phonon frequencies decrease with temperature. The E_2^{H} peak is at energy 54.44 meV (439.1 cm^{-1}), at 4 K and due to phonon-phonon anharmonic interaction, its energy decreases to 54.33 meV (438.2 cm^{-1}) at room temperature. The Grüneisen parameter found for this oscillation mode was γ_{E} 2H = 1.1 at about 300 K. The intensity of the E_2^{H} - E_2^{L} peak increases strongly with temperature and this dependence can be described by the Bose-Einstein statistics with activation energy of 13.8 meV (nearly equal to the energy of the E_2^{L} phonon).
12
Content available remote Photoluminescence Dynamics of GaN/Si Nanowires
75%
Korona K. , Zytkiewicz Z. , Perkowska P. , Borysiuk J. , Binder J. , Sobanska M. , Klosek K.
|
|
nr 6
1001-1003
EN
In this work we present analysis of carriers dynamics in samples of GaN nanowires grown on silicon. The samples exhibit bright luminescence of bulk donor-bound excitons at 3.472 eV, surface defect-bound excitons at 3.450 eV (SDX) and a broad (0.05 eV) band centered at 3.47 eV caused probably by single free exciton and bi-exciton recombination. The SDX emission has long lifetime τ = 0.6 ns at 4 K and can be observed up to 50 K. At higher temperatures luminescence is dominated by free excitons. The broad excitonic band is best visible under high excitation, and reveals fast, non-exponential dynamics. We present mathematical model assuming exciton-exciton interaction leading to the Auger processes. The model includes n^2 (Langevin) term and describes well the non-exponential dynamics of the excitonic band.
13
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.
14
Content available remote Highly Compensated GaAs Crystal Obtained by Molecular CO Doping
75%
Bożek R. , Korona K. , Nowak G. , Wasik D. , Słupiński T. , Kaczor P.
Acta Physica Polonica A
|
1993
|
tom 84
|
nr 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.
15
Content available remote Optical and Electrical Measurements of Low-Temperature InAlAs
75%
Korona K. , Wysmołek A. , Bożek R. , Kamińska M. , Baranowski J. , Weber E.
Acta Physica Polonica A
|
1992
|
tom 82
|
nr 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.
16
Content available remote InGaN QW in External Electric Field Controlled by Pumping of 2D-Electron Gas
75%
Korona K. , Drabińska A. , Surowiecka K. , Wołowiec L. , Borysiuk J. , Caban P. , Strupiński W.
Acta Physica Polonica A
|
2008
|
tom 114
|
nr 5
1179-1186
EN
We present investigations of GaInN/GaN/AlGaN structure containing cavity designed so that the electric field inside it can be changed by illumination. Numerical calculations show that illumination can change carrier distributions and consequently change the field and potential. The electric field influences properties of a quantum well placed in the cavity. We confirmed experimentally that the electric field controlled by external bias or by optical pumping, can change energy and occupation of electronic states in the quantum well. The quantum well energy could be changed of about 80 meV by voltage and 15 meV by illumination.
17
Content available remote A Model of Radiative Recombination in (In,Al,Ga)N/GaN Structures with Significant Potential Fluctuations
75%
Dróżdż P. , Korona K. , Sarzyński M. , Czernecki R. , Skierbiszewski C. , Muzioł G. , Suski T.
Acta Physica Polonica A
|
2016
|
tom 130
|
nr 5
1209-1212
EN
The potential fluctuations in III-nitride quantum wells lead to many effects like emission broadening and S-shape energy vs. temperature dependence. The best description of the energy dependence comes from calculations based on Gaussian density of states. However, in most of the published reports, changes of carrier lifetime with energy and temperature are not taken into account. Since experimental evidence shows that lifetime significantly depends on energy and temperature, here we propose a model that describes two basic parameters of luminescence: lifetime of carries and emission energy as a function of temperature in the case of quantum wells and layers that are characterized by potential fluctuations. Comparison of the measured energy and lifetime dependences on temperature in specially grown InGaN/GaN quantum wells and InAlGaN layer shows very good agreement with the proposed theoretical approach.
18
Content available remote FFirst TSC and DLTS Measurements of Low Temperature GaAs
75%
Muszalski J. , Babiński A. , Korona K. , Kamińska E. , Piotrowska A. , Kamińska M. , Weber E.
Acta Physica Polonica A
|
1991
|
tom 80
|
nr 3
413-416
EN
The first thermally stimulated current (TSC) and deep level transient spectroscopy (DLTS) studies performed on GaAs grown by molecular beam epitaxy (MBE) at low substrate temperatures (LT GaAs) are reported. TSC experiments, conducted on as grown and 400-580°C annealed layers showed domination of arsenic antisite (EL2-like) defect and supported its key role in hopping conductivity. DLTS studies, performed on Si doped and annealed at 800°C layers revealed substantially lower concentration of EL2-like defect and an electron trap of activation energy ΔE = 0.38 eV was found.
19
Content available remote Absorption and Emission Properties of Light Emitting Diode Structures Containing GaInN/GaN QWs
75%
Binder J. , Korona K. , Borysiuk J. , Wysmołek A. , Baeumler M. , Köhler K. , Kirste L.
Acta Physica Polonica A
|
2011
|
tom 120
|
nr 5
918-920
EN
In this work we present measurements of GaInN/GaN light emitting diodes (LEDs) with an active layer consisting of three quantum wells made of Ga_{0.9}In_{0.10}N that have different widths (1.8 nm, 2.7 nm, 3.7 nm). A comparison of emission and absorption (photocurrent) on the same sample revealed a shift in energy, with the emission energy being significantly lower. The shifts are about 0.02 eV, 0.03 eV, and 0.04 eV for the quantum wells having the widths of 1.8 nm, 2.7 nm, and 3.7 nm, respectively. This can be explained by a shift of the ground state energy caused by the quantum confined Stark effect. Calculations show that due to the spontaneous polarization and the piezoelectric effect a strong electric field of the order of 1 MV/cm was present in the GaInN quantum wells. Simulations of ground-state energies in the model of an infinite square well under the influence of an electric field with a matched effective well width were performed and used to interpret the experimental results.
20
Content available remote Raman Spectroscopy of LiFePO_4 and Li_3V_2(PO_4)_3 Prepared as Cathode Materials
75%
Ziółkowska D. , Korona K. , Kamińska M. , Grzanka E. , Andrzejczuk M. , Wu S. , Chen M.
Acta Physica Polonica A
|
2011
|
tom 120
|
nr 5
973-975
EN
Structure of samples of lithium iron vanadium phosphates of different compositions were investigated by X-rays, electron microscopy and Raman spectroscopy. The investigated salts were mainly of olivine-like and NASICON-like structures. The X-ray diffraction and the Raman scattering show different crystalline structures, which is probably caused by difference between cores of the crystallites (probed by X-rays) and their shells (probed by the Raman scattering). Most of the Raman spectra were identified with previously published data, however in the samples with high vanadium concentration we have observed new, not reported earlier modes at 835 cm^{-1} and 877 cm^{-1}, that we identified as oscillations related to V_2O_7^{4-} or VO_4^{3-} anions.
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