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1
Content available remote

Optically Detected Magnetic Resonance Studies of Te-Related Shallow Donors in Al_{x}Ga_{1-x}As

100%
Godlewski M., Fronc K., Chen W., Monemar B.
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issue 3
341-344
EN
The first studies of the Optically Detected Magnetic Resonance (ODMR) of Te-doped (x = 0.42) are presented. The ODMR data indicate an efficient energy transfer between epilayer and GaAs substrate.
2
Content available remote

Excitation and Recombination Processes in InAs_{x}P_{1-x}:Yb (x=0.04, 0.07 and 0.11)

88%
Godlewski M., Kozanecki A., Karpińska K., Bergman J. P., Monemar B.
Acta Physica Polonica A
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1995
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vol. 87
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issue 1
217-220
EN
Excitation and recombination mechanisms of Yb^{3+} 4f-4f intra-shell emission in InP and InAsP (4, 7 and 11% of As) are analyzed.
3
Content available remote

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.
4
Content available remote

Optical Properties of GaN Epilayers grown by Gas Source Molecular Beam Epitaxy on AlN Buffer Layer on (111) Si

88%
Godlewski M., Bergman J., Monemar B., Rossner U., Barski A.
Acta Physica Polonica A
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1996
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vol. 90
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issue 4
789-792
EN
Optical properties of GaN/AlN/Si (111) epilayers grown by MBE are studied. The observed decay transients of excitonic emissions and their temperature dependence is explained by an efficient transfer link between bound and free excitons.
5
Content available remote

Impact Ionization Driven Chaotic Photoluminescence Oscillations in Ga_{0.47}In_{0.53}As

88%
Godlewski M., Fronc K., Gajewska M., Chen W., Monemar B.
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issue 2
271-274
EN
A new application of the Optically Detected Cyclotron Resonance (ODCR) is presented. We report impact ionization studies of bound exciton: (BE) and shallow donor related recombination processes in Ga_{0.47}In_{0.53}As. An appearance of chaotic oscillations in photoluminescence (PL) intensity is observed under condition of impact ionization of deeper donors.
6
Content available remote

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.
7
Content available remote

Optically Detected Cyclotron Resonance Studies of CdMnTe/CdTe Multiquantum Wells and CdMgTe/CdMnTe Superlattices

76%
Godlewski M., Świątek K., Harris C. I., Bergman J. P., Monemar B., Waag A.
Acta Physica Polonica A
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1995
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vol. 87
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issue 1
213-216
EN
The results of photoluminescence, time resolved photoluminescence (de­cay times), optically detected cyclotron and magnetic resonances investiga­tions of CdMnTe/CdTe multiquantum wells and CdMgTe/CdMnTe super-lattices are presented. The role of defects and quantum well width fluctua­tions in recombination processes of 2D carriers is discussed.
8
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Content available

Carrier Diffusion in the Barrier Enabling Formation of Charged Excitons in InAs/GaAs Quantum Dots

76%
Karlsson K., Moskalenko E., Holtz P., Monemar B., Schoenfeld W., Garcia J., Petroff P.
Acta Physica Polonica A
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2001
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vol. 100
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issue 3
387-395
EN
It is demonstrated that the photoluminescence spectra of single self-assembled quantum dots are very sensitive to the experimental conditions, such as excitation energy and crystal temperature. A qualitative explanation is given in terms of the effective diffusion of the photogenerated carriers, determined by the experimental conditions, which influence the capture probability and hence also the charge state of the quantum dots. This is proposed as a new tool to populate quantum dots with extra electrons in order to study phenomena involving charged excitons.
9
Content available remote

Fermi-Edge Singularity in Excitonic Spectra of Modulation Doped AlGaAs/GaAs Quantum Wells

76%
Bugajski M., Regiński K., Godlewski M., Wesołowski M., Holtz P., Buyanov A., Monemar B.
Acta Physica Polonica A
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1996
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vol. 90
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issue 4
751-754
EN
The dynamic response of an electron Fermi sea to the presence of optically generated holes gives rise to an enhanced interaction of correlated electron-hole pairs near the Fermi level, resulting in an enhanced oscillator strength for optical transitions, referred to as the Fermi-edge singularity. We studied this effect in modulation-doped quantum wells which provide confined dense Fermi sea, spatially separated from dopant atoms, easily accessible for investigations under low excitation conditions. The Fermi-edge singularity was observed in both photoluminescence and photoluminescence excitation experiments, although in the case of photoluminescence the samples had to be either co-doped with acceptors in the wells to provide necessary localization of holes or designed to allow for nearly resonant scattering between the electronic states near the Fermi energy and the next unoccupied subband of the 2D electron gas.
10
Content available remote

Transport Properties of Silicon δ-Doped Gaas in High Electron Density Regime

76%
Buyanov A. V., Holtz P. O., Pozina G., Monemar B., Thordson J., Andersson T. G.
Acta Physica Polonica A
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1997
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vol. 92
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issue 4
727-732
EN
We report results for Si layers embedded in GaAs, extending from the delta-doped (δ-doped) range up to 6 monolayers derived by means of variable temperature resistivity and Hall effect measurements, secondary ion mass spectrometry and high resolution X-ray diffractometry techniques. The conductivity transition from free carrier transport in ordered δ-layers (<1 ML) to strongly-localized two-dimensional variable range hopping transport under potential fluctuation disordered conditions (>4 ML) is clearly observed. This observation is in good agreement with the secondary ion mass spectrometry and high resolution X-ray diffractometry data. Results from the intermediate case with 2-3 MLs are also discussed.
11
Content available remote

Photoluminescence Studies of Cubic Phase GaN Grown by Molecular Beam Epitaxy on (001) Silicon Covered with Sic Layer

76%
Godlewski M., Ivanov V., Bergman J., Monemar B., Barski A., Langer R.
Acta Physica Polonica A
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1997
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vol. 92
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issue 4
777-780
EN
In this work we evaluate optical properties of cubic phase GaN epilayers grown on top of (001) silicon substrate prepared by a new process. Prior to the growth Si substrate was annealed at 1300-1400°C in propane. The so-prepared substrate is covered with a thin (≈ 4 nm) SiC wafer, which allowed a successful growth of good morphological quality cubic phase GaN epilayers. The present results confirm recent suggestion on smaller ionization energies of acceptors in cubic phase GaN epilayers.
12
Content available remote

Hot Photoluminescence in CdTe/CdMnTe Quantum Well Structures Grown by Molecular Beam Epitaxy

76%
Godlewski M., Wojtowicz T., Karczewski G., Kossut J., Bergman J. P., Holtz P. O., Monemar B.
Acta Physica Polonica A
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1997
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vol. 92
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issue 4
765-768
EN
A step-like emission is observed for CdTe/CdMnTe structures δ-doped with In. The new photoluminescence cannot be explained by neither the Raman process nor by the "ordinary" hot photoluminescence. We propose that magnetic interactions are responsible for the new photoluminescence appearing due to a dramatic increase in a thermalization time of hot excitons.
13
Content available remote

Exciton Properties in CdTe/CdMnTe Quantum Well Structures with Strong Localization Effects

76%
Godlewski M., Narkowicz R., Wojtowicz T., Karczewski G., Kossut J., Bergman J., Monemar B.
Acta Physica Polonica A
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1998
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vol. 94
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issue 2
317-320
EN
Strong localization effects present in quantum well structures of CdTe/ CdMnTe noticeably affect exciton dynamics and strength and character of exciton-phonon interaction. We show that the temperature dependences of the PL linewidth, PL peak wavelength and PL decay time strongly deviate from those expected for Wannier-excitons in structures with atomically smooth interfaces.
14
Content available remote

Influence of Well-Width Fluctuations on the Electronic Structure of GaN/Al_xGa_{1-x}N Multiquantum Wells with Graded Interfaces

76%
Valcheva E., Dimitrov S., Monemar B., Haratizadeh H., Persson P., Amano H., Akasaki I.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
395-400
EN
Experimental and computation results based on chemical composition assessment of metal-organic chemical vapour deposition grown undoped GaN/Al_xGa_{1-x}N multiquantum well structures in the low composition limit of x = 0.07 and wide wells demonstrate composition fluctuations in the barrier layers which lead to large-scale nonuniformities and inequivalence of the different wells. As a consequence the experimental photoluminescence spectra at low temperature show a double peak structure indicative of well-width fluctuations by one lattice parameter (2 monolayers).
15
Content available remote

Recombination Processes in Doped CdTe/CdMnTe Multiple Quantum Well Structures Grown by Molecular Beam Epitaxy

76%
Godlewski M., Wojtowicz T., Karczewski G., Kossut J., Bergman J. P., Monemar B.
Acta Physica Polonica A
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1997
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vol. 92
|
issue 4
757-760
EN
An influence of doping level on exciton properties in n-doped multiple quantum well structures of CdTe/CdMnTe is studied for multiple quantum well structures prepared in the way that donor (indium) concentration changes within the length of the sample. We show that the formation scenario for neutral donor bound excitons in low-dimensional structures can be different from that observed in bulk samples. We further show that in the case of such quantum well structures we can selectively excite either photoluminescence emission of localized or donor bound excitons, which is a consequence of surprisingly weak energy transfer link between two types of excitonic transitions.
16
Content available remote

Fermi-Edge Singularity in Luminescence Spectra of P-Type Modulation Doped AlGaAs/GaAs Quantum Wells

76%
Bugajski M., Godlewski M., Regiński K., Holtz P., Bergman J., Monemar B.
Acta Physica Polonica A
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1998
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vol. 94
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issue 2
265-270
EN
We have studied an enhancement of the oscillator strength for optical transitions near the Fermi energy in p-type modulation-doped quantum wells, which, so far, deserved much less attention than analogous n-type systems, because of the complicated valence band structure involved. The relatively wide (L=150 Å) quantum wells and high doping levels were used, containing more than one occupied subband. The enhancement in the photoluminescence intensity at the Fermi energy resulted from the strong correlation and multiple scattering of holes near the Fermi edge by the localized electrons.
17
Content available remote

Theoretical and Experimental Study of the Radiative Decay Process in a Modulation Doped GaAs/AlGaAs Heterointerface

76%
Lundström T., Bergman J. P., Holtz P. O., Monemar B., Campman K., Merz J. L., Gossard A. C.
Acta Physica Polonica A
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1997
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vol. 92
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issue 4
824-828
EN
We have theoretically and experimentally investigated the radiative recombination process in an n-type modulation doped GaAs/Al_{0.35}Ga_{0.65}As heterostructure. The dynamical reshaping of the potential profile across the heterojunction, and the decay of the spatially indirect radiative recombination between electrons in the two-dimensional electron gas and photo-created holes, have been numerically simulated for various values of the electric field across the heterojunction. Optical matrix elements were deduced from a self-consistent solution of the coupled Schrodinger and Poisson equations at every discrete point of time. The calculated recombination energies and integrated luminescence intensities were compared with experimental data from time-resolved photoluminescence measurements on an 800 Å wide GaAs/AlGaAs heterostructure.
18
Content available remote

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
|
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.
19
Content available remote

Inter-Island Energy Transfer in AlGaAs/GaAs Quantum Wells Grown by Molecular Beam Epitaxy

76%
Godlewski M., Holz P., Bergman J., Monemar B., Regiński K., Bugajski M.
Acta Physica Polonica A
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1996
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vol. 90
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issue 5
1007-1011
EN
The results of photoluminescence, time-resolved photoluminescence, photoluminescence excitation and photoluminescence kinetics studies are presented for a Al_{0.3}Ga_{0.7}As/GaAs quantum well system grown without growth interruptions at the interfaces. The time-resolved photoluminescence measurements show drift of excitons towards lower energy states induced in a quantum well by potential fluctuations. We present also a first direct evidence for migration of free excitons from the 24 to 25 ML regions of the quantum well and interpret these results within a linear rate model, deriving the transition rate of 290 ps^{-1}. Such inter-island migration processes have been observed till now only in growth interrupted structures.
20
Content available remote

Comparison of Optical Properties of CdTe/CdMnTe Quantum Wells Grown by Molecular Beam and Atomic Layer Epitaxy

76%
Godlewski M., Kopalko K., Wojtowicz T., Karczewski G., Kossut J., Bergman J., Monemar B.
Acta Physica Polonica A
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1996
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vol. 90
|
issue 5
1012-1016
EN
Optical properties of a series of CdTe/CdMnTe multi quantum well structures grown with MBE and ALE (CdTe quantum wells only) methods are compared. Based on the results of the photoluminescence experiments we conclude that the ALE growth leads to a different lateral scale of quantum well width fluctuations, which results in different exciton properties in two multi quantum well systems studied. In the wells grown with ALE method excitons are less localized. They can migrate in a quantum well plane between quantum well regions varying in thickness by 1 monolayer.
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