Search results

1

Charging Effects in Self-Assembled CdTe Quantum Dots

100%

Kłopotowski Ł.

Acta Physica Polonica A

|

2011

|

vol. 120

|

issue 5

819-829

EN

In this review, we summarize our achievements in controlling and understanding the charging effects in single self-assembled CdTe quantum dots. We start with analysis of the single dot emission spectrum. For excitation densities small enough to ensure only s-shell recombination, we find that for all dots (also those reported by other groups) the same transition sequence is observed. Namely, the neutral exciton recombination has the highest energy while charged exciton and biexciton transitions are redshifted. This observation remains in a stark contrast to self-assembled InGaAs dots, where charged complexes may appear also on the high energy side of the neutral exciton. We explain the universality of the transition sequence assuming domination of the Coulomb correlations over direct, single particle interactions. Furthermore, through measurement of the recombination rates, we gain access to electron and hole wave functions and their redistributions upon changing the dot occupancy. We find that the electron wave function is rather stiff, while the hole wave function is rather soft owing to enhanced correlations in the valence band. We then corroborate these conclusions with the Stark spectroscopy, where we analyze energy shifts due to electric field imposed on dots embedded in a field effect or diode structure. Finally, we use these structures to obtain controllable tuning of the charge state. We discuss different approaches to this task and find the best tuning efficiency for a structure with enhanced valence band confinement.

2

Optical Properties of a Semimagnetic Quantum Well in a Proximity of a Superconducting Film

51%

Lebecki K., Kłopotowski Ł., Kossut J.

Acta Physica Polonica A

|

2005

|

vol. 108

|

issue 5

741-748

EN

We consider, via numerical calculations, a hybrid structure made of a semimagnetic Cd_{1-x}Mn_xTe quantum well deposited in a close proximity to superconducting niobium film. We simulate photoluminescence and the Faraday rotation spectra, modified by the presence of vortices in this type II superconductor. The magnitude of the evaluated effects is small - the vortex induced spectral line shape variation is of the order of 1% at 1 K and 0.1% at 3 K and is expected to occur mainly in the field range between 0.03 T and 0.05 T.

3

Time-Resolved Emission from Semiconductor Microcavities

45%

Kłopotowski Ł., Viña L., Kavokin A., Dang L., André R.

Acta Physica Polonica A

|

2004

|

vol. 106

|

issue 3

435-442

EN

We present a time-resolved study of the light emission of a CdTe-based microcavity. In the nonlinear regime, under high excitation conditions, in the strong coupling regime, we observe pronounced beats of the intensity of the photoluminescence arising from the bottleneck region of the exciton-polariton band. These beats are very sensitive to the excitation density and vanish under weak pumping conditions. We attribute the beats to a new nonlinear coupling mechanism of optically active and dark crystal states, related to polariton-polariton scattering, which leads to mixing between bright and dark states.

4

Identification of Optical Transitions from CdTe and CdMnTe Quantum Dots Embedded in ZnTe Nanowires

39%

Szymura M., Kłopotowski Ł., Wojnar P., Karczewski G., Wojtowicz T., Kossut J.

Acta Physica Polonica A

|

2013

|

vol. 124

|

issue 5

824-826

EN

We study photoluminescence properties of CdTe and CdMnTe quantum dots embedded in ZnTe nanowires. The nanowires were grown by molecular beam epitaxy, applying the vapor-liquid-solid growth mechanism. Linear polarization anisotropy measurements allow us to assess that the excitonic transitions originate from a single nanowire. We identify the optical transitions by comparing observed spectroscopic shifts with the universal emission pattern from the epitaxial CdTe dots. We support this identification by analyzing the photoluminescence intensity dependence on excitation power.

5

Dynamics of Polariton Emission in the Linear Regime

39%

Kłopotowski Ł., Santos R., Amo A., Martín M., Viña L., André R.

Acta Physica Polonica A

|

2004

|

vol. 106

|

issue 3

443-450

EN

We studied the dependence of polariton emission dynamics on polariton wave-vector and exciton-photon energy detuning. To reproduce the experimental data, we applied a model that obtains the photonic and the excitonic emission rates of the polariton.

6

Optical Study of ZnTe-Based 2D and 0D Photonic Structures Containing CdTe/ZnTe Quantum Dots

33%

Jakubczyk T., Kazimierczuk T., Golnik A., Bienias P., Pacuski W., Kruse C., Hommel D., Kłopotowski Ł., Wojtowicz T., Gaj J.

Acta Physica Polonica A

|

2009

|

vol. 116

|

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.

7

Spectroscopy of Indirect Excitons in Vertically Stacked CdTe Quantum Dot Structures

33%

Kukliński K., Kłopotowski Ł., Fronc K., Wojnar P., Wojciechowski T., Czapkiewicz M., Kossut J., Karczewski G., Wojtowicz T.

Acta Physica Polonica A

|

2011

|

vol. 120

|

issue 5

856-858

EN

We show that by means of an electric field we can tune the energy levels in vertical quantum dot pairs and study transitions related to recombination of direct and indirect excitons. With decreasing the reverse bias, we observe both the blue- and red-shifted indirect exciton transitions. Based on the band profile of our device, we conclude that the former corresponds to the recombination of the electron and hole localized in the top and the bottom dot, respectively and the latter is related to the recombination of the electron and hole localized in the bottom and the top dot, respectively.

8

Photoluminescence Properties of ZnO Nanowires Grown on Ni Substrate

27%

Zaleszczyk W., Fronc K., Przeździecka E., Janik E., Czapkiewicz M., Wróbel J., Paszkowicz W., Kłopotowski Ł., Karczewski G., Wojtowicz T., Presz A.

Acta Physica Polonica A

|

2008

|

vol. 114

|

issue 5

1451-1456

EN

Photoluminescence studies of zinc oxide nanowires produced by a carbo-thermal method on a nickel foil substrate are reported. Two types of as-grown samples: the first - containing only buffer film, and the second - containing both zinc oxide nanowires and buffer film grown in the same technological process, were investigated by means of the temperature-dependent photoluminescence. X-ray diffraction measurements of buffer film show that it is polycrystalline and is composed from wurtzite-type ZnO (main phase) and includes minority phases: rock salt type (Ni,Zn)O and hexagonal C₃N₄. The shape of the apparently monocrystalline nanowires is characterized by hexagonal section matching with the expectations of the hexagonal ZnO structure. The presence of LO-phonon replicas in photoluminescence spectra for the second sample is used as an argument for confirmation that ZnO nanowires are single crystalline. The method of growth of ZnO nanowires on nickel oxide opens perspectives to produce Zn_{1-x}Ni_{x}O diluted magnetic semiconductor nanowires.

9

Photoluminescence Properties of ZnO and ZnCdO Nanowires

27%

Zaleszczyk W., Fronc K., Aleszkiewicz M., Paszkowicz W., Wróbel J., Dłużewski P., Kret S., Klepka M., Kłopotowski Ł., Karczewski G., Wojtowicz T.

Acta Physica Polonica A

|

2007

|

vol. 112

|

issue 2

357-362

EN

We report on the photoluminescence studies of ZnO and ZnCdO nanowires grown on SiO_2/Si substrates by low-pressure vapor phase synthesis. X-ray diffraction and transmission electron microscopy measurements show that the crystallographic structure of these ZnO and ZnCdO nanowires is of wurtzite-type with a high crystal perfection. Surface morphology of samples was determined by scanning electron microscopy and atomic force microscopy. The photoluminescence spectra of as-grown nanowires, nanowires extracted from the substrate and deposited onto Si wafer, and nanowires dispersed in ethanol by sonication were investigated at room temperature and compared to each other. The temperature dependence of the near band-gap photoluminescence emitted by the as-grown nanowires was also measured and analyzed.

Refine search results

Charging Effects in Self-Assembled CdTe Quantum Dots

Optical Properties of a Semimagnetic Quantum Well in a Proximity of a Superconducting Film

Time-Resolved Emission from Semiconductor Microcavities

Identification of Optical Transitions from CdTe and CdMnTe Quantum Dots Embedded in ZnTe Nanowires

Dynamics of Polariton Emission in the Linear Regime

Optical Study of ZnTe-Based 2D and 0D Photonic Structures Containing CdTe/ZnTe Quantum Dots

Spectroscopy of Indirect Excitons in Vertically Stacked CdTe Quantum Dot Structures

Photoluminescence Properties of ZnO Nanowires Grown on Ni Substrate

Photoluminescence Properties of ZnO and ZnCdO Nanowires