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1
Content available remote On the Pinning of the Fermi Level by Germanium A_{1}^{0/+} Deep Donor State in GaAs Codoped with Ge and Te
100%
Słupiński T. , Nowak G. , Przybytek J. , Stępniewski R.
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nr 4
807-811
EN
We present the possibility of GaAs:Ge,Te crystals growth from the melt (liquid encapsulated Czochralski method) with partially occupied, at ambient pressure, the A_{1} localized electronic state of Ge_{Ga} impurity. In as-grown crystals the amphotericity of Ge and creation of defects (deep acceptor complexes, precipitates etc.) during cooling after growth limit the free electron concentration below the value necessary to populate the A_{1}^{0/+} level. Special annealing of the samples, which enlarges the free electron concentration, was used. The occupation of A_{1}^{0/+} level, at ambient pressure, was observed by pressure dependent Hall effect measurements.
2
Content available remote Exciton in 2D Cubic Inclusion in Hexagonal GaN
100%
Suffczyński M. , Stępniewski R. , Baranowski J.
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nr 5
993-996
EN
An inclusion of cubic GaN in an otherwise hexagonal matrix is considered to be equivalent to an effective quantum well. The exciton binding energy in a quantum well of a finite potential barrier height in the conduction and valence bands is calculated in the effective mass approximation with a variational envelope function type of Bastard and Takagahara. The exciton binding energy and the energy of exciton recombination line are computed, as a function of the well width, for realistic potential barrier heights and band-offset ratios.
3
Content available remote Dielectric Function Theory Calculations of Polaritons in GaN
100%
Korona K. P. , Stępniewski R. , Baranowski J. M.
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nr 5
867-869
EN
Properties of polaritons (free excitons coupled with photons of similar energy) in gallium nitride are investigated by performing calculations based on dielectric function theory including all three excitons A, B and C (characteristic for the wurtzite structure). Moreover the excited states of excitons have been taken into account by adding Elliott's components to dielectric function. Energies, polarizabilities and damping constants of excitons are determined. It is shown that due to inter-exciton interactions the B and C excitons are strongly damped. It is estimated that the characteristic time of B to A relaxation is t_{BA}=1 ps. The exciton C lifetime is estimated τ_{C}=0.2 ps.
4
Content available remote Infrared Optical and X-Ray Determination of Parameters for MOVPE Grown InAs_{1-x}Sb_{x} Epilayers
88%
Marszałek B. , Zielińska-Rohozińska E. , Bożek R. , Stępniewski R. , Witowski A.
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nr 5
919-922
EN
The experimental room-temperature transmission of metalorganic vapour phase epitaxy grown InAsSb epilayers is compared with calculations based on a Kane model of the band structure. The band structure parameters are found. The composition of the samples was determined by X-ray diffraction.
5
Content available remote Raman Piezospectroscopy of Phonons in Bulk 6H-SiC
75%
Grodecki K. , Wysmołek A. , Stępniewski R. , Baranowski J. , Hofman W. , Tymicki E. , Grasza K.
Acta Physica Polonica A
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2009
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tom 116
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nr 5
947-949
EN
Raman piezospectroscopy of high quality 6H-SiC crystals is presented. The crystals used in experiments were grown by the seeded physical vapor transport method. Uniaxial stress up to 0.9 MPa, obtained using a spring apparatus, was applied along [11-20] and [10-10] directions. It was found that the application of uniaxial stress led to different energy shifts of the observed phonon excitations in the investigated 6H-SiC crystals. The obtained pressure coefficients vary in the range 0.98-5.5 cm^{-1} GPa^{-1} for different transverse optical phonon modes. For longitudinal optic phonon modes pressure coefficients in the range 1.6-3.6 cm^{-1} GPa^{-1} were found. The data obtained could be useful in evaluation of local strain fields in SiC based structures and devices including epitaxial graphene.
6
Content available remote Graphene Based Flow Sensors
75%
Kaźmierczak P. , Binder J. , Boryczko K. , Ciuk T. , Strupiński W. , Stępniewski R. , Wysmołek A.
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nr 5
1209-1212
EN
We report on attempts to produce a graphene based liquid flow sensor. Our results indicate that modifications of the electric double layer, formed in the vicinity of the graphene surface, dominate over mechanisms responsible for liquid flow-induced voltage/current generation. Several graphene structures were tested in different measurement configurations, aimed to maximize the generated signal amplitude and its stability. Some realizations of working devices in water as well as in aqueous solutions of NaCl or HCl are presented.
7
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
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2009
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tom 116
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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.
8
Content available remote Single GaN/AlGaN Quantum Dot Spectroscopy
75%
Surowiecka K. , Wysmołek A. , Stępniewski R. , Bożek R. , Pakuła K. , Baranowski J.
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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.
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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 Raman Studies of Defects in Graphene Grown on SiC
75%
Grodecki K. , Bożek R. , Borysiuk J. , Strupinski W. , Wysmolek A. , Stępniewski R. , Baranowski J.
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nr 5
595-596
EN
The Raman scattering studies of multi-layer graphene obtained by high temperature annealing of carbon terminated face of 4H-SiC(000-1) substrates are presented. Intensity ratio of the D and G bands was used to estimate the average size of the graphene flakes constituting carbon structures. The obtained estimates were compared with flake sizes from atomic force microscopy data. We found that even the smallest structures observed by atomic force microscopy images are much bigger than the estimates obtained from the Raman scattering data. The obtained results are discussed in terms of different average flake sizes inside and on the surface of the multi-layer graphene structure, as well as different type of defects which would be present in the investigated structures apart from edge defects.
11
Content available remote Optical Absorption and Raman Scattering Studies of Few-Layer Epitaxial Graphene Grown on 4H-SiC Substrates
63%
Grodecki K. , Drabińska A. , Bożek R. , Wysmołek A. , Korona K. , Strupiński W. , Borysiuk J. , Stępniewski R. , Baranowski J.
Acta Physica Polonica A
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2009
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tom 116
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nr 5
835-837
EN
Optical absorption and Raman scattering studies of few-layer epitaxial graphene obtained by high temperature annealing of carbon terminated face of 4H-SiC(000-1) on-axis substrates are presented. Changing the pressure and annealing time, different stages of the graphene formation were achieved. Optical absorption measurements enabled us to establish average number of graphene layers covering the SiC substrate. Raman scattering experiments showed that integrated intensity of the characteristic 2D peak positively correlated with the number of graphene layers deposited on the SiC substrate. The spectral width of the 2D peak was found to decrease with the number of the deposited graphene layers.
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