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1
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CdSe Layers of Below Critical Thickness in ZnSe Matrix: Intrinsic Morphology and Defect Formation

100%
Sedova I., Shubina T., Sorokin S., Sitnikova A., Toropov A., Ivanov S., Willander M.
Acta Physica Polonica A
|
1998
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vol. 94
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issue 3
519-525
EN
Three main stages of the intrinsic morphology transformation of MBE grown CdSe fractional monolayers in ZnSe with increase in their nominal thickness w in the 0.1-3.0 monolayer range were found using both structural and optical characterization techniques. Emergence of the extended (15-30 nm) CdSe-enriched quantum-dot-like pseudomorphic islands at w>0.7 monolayer with the density increasing up to 2.5×10^{10} cm^{-2} at w=2.8 monolayer is clearly displayed in the optical properties of CdSe fractional monolayer nanostructures. The below critical thickness CdSe fractional monolayers having extremely high quantum efficiency can be very perspective as an active region of ZnSe-based blue-green lasers.
2
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Stimulated and Laser Emission in CdZnTe/CdMnTe Double Quantum Well Heterostructures

63%
Kowalczyk L., Karczewski G., Wojtowicz T., Kossut J.
Acta Physica Polonica A
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1995
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vol. 88
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issue 4
787-790
EN
Stimulated emission by optical excitation has been investigated in CdZnTe/CdMnTe quantum well heterostructures. Laser action has been achieved at 4.2 K and at 77 K with relatively low threshold values of the excitation intensity. Photοluminescence excitation spectra of the stimulated emission were obtained indicating that the optical gain involves exciton-exci­ton inelastic scattering.
3
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Disordered Nd-Doped Crystals for Diode Pumping

63%
Ryba-Romanowski W.
Acta Physica Polonica A
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1993
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vol. 84
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issue 5
945-952
EN
Some interest has been directed recently to neodymium doped crystals with strong inhomogeneous broadening of absorption bands which are believed to be better suited for diode pumping than the crystals with ordered lattice. The disordered Nd-doped crystals may be obtained in two ways. The first one is to introduce a structural disorder in ordered lattice by substituting partially one or more cations by cations with different charges. Alternatively, the compounds with inherently disordered structure are synthesized and doped with Nd. We consider two wide families of compounds of general formulae ABC_{3}O_{7} and ABCO_{4} where A stands for Ca, Sr, Ba, B is Y or rare earth and C stands for Ga or Al. Both the families form the crystals with inherently disordered structure and can accept an appreciable amount of Nd. Results of structural and spectroscopic investigations are used to determine material's parameters relevant to laser performance. Comparison of several disordered crystals is made and their suitability for diode pumping is discussed.
4
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Optically Pumped Low Threshold ZnSe Based Lasers with 2.8 ML CdSe Active Region

63%
Sorokin S., Toropov A., Shubina T., Lebedev A., Sedova I., Ivanov S., Waag A.
Acta Physica Polonica A
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1998
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vol. 94
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issue 3
539-544
EN
Room-temperature optically pumped (Zn,Mg)(S,Se)/(Zn,Cd)Se laser structures have been grown by molecular beam epitaxy. Using of alternatively-strained short-period superlattice waveguide results in low threshold power density values over the whole blue-green (470-520 nm) wavelength range. Incorporation of CdSe fractional monolayer active region provides more than fourfold further decrease in threshold with respect to quantum well laser structure. Optical and structural properties of laser structure with 2.8 monolayer CdSe are discussed in detail.
5
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The Effect of Pressure and Temperature on AlGaInP and AlGaAs Laser Diodes

51%
Adamiec P., Świetlik T., Bohdan R., Bercha A., Dybała F., Trzeciakowski W.
Acta Physica Polonica A
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2003
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vol. 103
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issue 6
585-593
EN
InGaP/AlGaInP lasers (emitting from 630 to 690 nm) and GaAs/AlGaAs lasers (emitting at 780 nm) were studied under hydrostatic pressure up to 20 kbar and at temperatures from 240 to 300 K. The electrical characteristics, the power-current dependencies and the emission spectra were measured. The emission spectra shifted in agreement with the pressure/temperature variation of the band gaps in active layers of the laser. Since at high pressure theΓ-X separation in the conduction band is strongly reduced (both in AlGaInP and AlGaAs), the dominant loss mechanism of the lasers is the electron leakage to X minima in the p-claddings. This, in turn, leads to high sensitivity of threshold currents to temperature. The dependence of threshold currents on pressure and on temperature is in good agreement with the simple theoretical analysis taking into account the carrier leakage and the radiative and nonradiative recombination. Better agreement between the theory and the experiment is obtained assuming drift rather than diffusion leakage. This indicates that threshold currents could be further reduced if the p-doping is improved in the claddings.
6
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Optically Pumped Laser Action on Nitride Based Separate Confinement Heterostructures Grown along the (11¯20) Crystallographic Direction

51%
Teisseyre H., Szymański M., Khachapuridze A., Skierbiszewski C., Feduniewicz-Żmuda A., Siekacz M., Łucznik B., Kamler G., Kryśko M., Suski T., Perlin P., Grzegory I.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
467-472
EN
The intention of this work is to discuss and report on our research on nonpolar laser structures grown on bulk GaN crystal substrates along the (11¯20) nonpolar direction. The main advantages of such nonpolar structures are related to the elimination of the built-in electric fields present in commonly used systems grown along the polar (0001) axis of nitride crystals. We demonstrated the optically pumped laser action on separate confinement heterostructures. Laser action is clearly shown by spontaneous emission saturation, abrupt line narrowing, and strong transversal electric polarization of output light. The lasing threshold was reached at an excitation power density of 260 kW/cm^2 for a 700μm long cavity (at room temperature).
7
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Luminescence in Highly Excited InGaN/GaN Multiple Quantum Wells Grown on GaN and Sapphire Substrates

51%
Miasojedovas S., Juršėnas S., Kurilčik G., Žukauskas A., Ivanov V., Godlewski M., Leszczyński M., Perlin P., Suski T.
Acta Physica Polonica A
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2004
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vol. 106
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issue 2
273-279
EN
We report on high-excitation luminescence spectroscopy in In_xGa_{1-x}N/GaN multiple quantum wells grown by MOCVD over sapphire and bulk GaN substrates. High excitation conditions enabled us to achieve a screening of the built-in field by free carriers. This allowed for the evaluation of the influence of band potential fluctuations due to the variation in In-content on efficiency of spontaneous and stimulated emission. InGaN/GaN multiple quantum wells grown on bulk GaN substrate exhibit a significantly lower stimulated emission threshold and thus enhanced lateral emission. Transient and dynamic properties of luminescence indicate a significant reduction in compositional disorder in homoepitaxially grown structures
8
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Excitonic Polaritons in Semiconductor Micropillars

51%
Bajoni D., Wertz E., Senellart P., Miard A., Semenova E., Lemaître A., Sagnes I., Bouchoule S., Bloch J.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
933-943
EN
We describe the physics of cavity polaritons in semiconductor micropillars. Cavity polaritons are exciton-photon entangled states arising from the strong coupling between excitons and the optical modes of a cavity. In micropillars, the photon three-dimensional confinement results in a discrete spectrum of 0D polariton states. Characterization of the linear properties of these micropillars will be presented. Then we will show how this system can be used to generate parametric photons and to obtain polariton lasing.
9
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High Quality ZnSe and Zn(Se,S) Produced by Low Temperature Physical Vapour Transport

51%
Mycielski A., Szadkowski A., Kowalczyk L., Zaręba A.
Acta Physica Polonica A
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1996
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vol. 90
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issue 5
1050-1054
EN
High quality, large (25 mm in diameter) crystals of ZnSe and Zn(Se,S) were grown by low-temperature physical vapour transport method and characterized by various techniques, i.e. energy dispersive X-ray fluorescence spectrometry, double-crystal X-ray diffraction rocking curve FWHM, reflectivity measurements in the region of free exciton, electrical measurements and photoluminescence measurements for both low and high excitation densities. The measurement of the photoluminescence related to the neutral-donor-bound exciton revealed superlinear log(photoluminescence intensity) versus log(excitation intensity) dependence, which indicates stimulated emission phenomena.
10
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Investigation of the Active Ions Distribution in Laser Crystals Using High Resolution Spectroscopy

51%
Pelletier-Allard N., Pelletier R.
Acta Physica Polonica A
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1996
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vol. 90
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issue 1
143-150
EN
High resolution spectroscopy techniques are used to investigate the distribution of rare-earth ions inside crystal hosts and their transfer properties. Examples concerning two typical laser materials are treated.
11
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Stimulated Emission in Zn(Se,S) Single Crystals

51%
Kowalczyk L., Mycielski A., Szadkowski A., Testelin C., Rigaux C., Menant M.
Acta Physica Polonica A
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1997
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vol. 92
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issue 5
871-874
EN
Two different types of optically pumped stimulated emission were observed at 1.8 K in the high quality Zn(Se,S) crystals grown by low temperature physical vapour transport. One type, occurring at moderate excitation levels, is ascribed to the recombination of excitons localized because of chemical disorder in the two-anion mixed crystal. The other type, occurring at high excitation levels, is related to the inelastic exciton-exciton scattering.
12
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Stimulated Emission in InGaN/GaN Multiple Quantum Wells with Different Indium Content

51%
Miasojedovas S., Juršėnas S., Kurilčik G., Žukauskas A., Springis M., Tale I., Yang C.
Acta Physica Polonica A
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2005
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vol. 107
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issue 2
256-260
EN
We report on high-excitation luminescence spectroscopy of In_xGa_{1-x}N/GaN multiple quantum wells with a high indium content (x=0.22÷0.30). High excitation conditions enabled us to achieve screening of built-in field by free carriers. This allowed for the evaluation of the influence of the band potential fluctuations due to variation in In-content on optical properties. Enhanced spontaneous emission was found for x≫0.22 due to carrier localization within the chaotic band potential. Meanwhile the stimulated emission was found to be the highest for structures with x≈ 0.25-0.27. We attribute the In-content dependence of the stimulated emission intensity to a trade-off between an increased carrier density and a decrease in the density of states.
13
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Transient Response of Electrons and Phonons in ZnTe Crystals

51%
Brazis R., Raguotis R.
Acta Physica Polonica A
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2008
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vol. 113
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issue 3
933-936
EN
The response of electron and phonon ensemble to the switching on and off electric field E in n-type ZnTe crystals is simulated by Monte Carlo method. The results at T=10 K show significant accumulation of LO-phonons and the LO phonon band population inversion with respect to the LA band;the inversion is necessary for the stimulated transfer of LO-LA energy difference to photons. The maximum inversion is at E=7 kV/cm. At T=300 K no phonon band inversion but fast (sub-picosecond) drift velocity switching with ≈100 GHz repetition is feasible.
14
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Excitons and Phonons in GaN. Magnetooptical and Spatially Resolved Investigations

51%
Hoffmann A., Eckey L., Siegle H., Kaschner A., Christen J., Bertram F., Liu Q.
Acta Physica Polonica A
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1998
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vol. 94
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issue 2
125-137
EN
A comprehensive study of the direct photoluminescence from free-exciton states in GaN using polarization-dependent and magnetooptical measurements is presented. We measured and identified fine-structure splittings in the n=1 state of the A-exciton. From the magnetoluminescence data obtained in fields up to 15 T we determined the g-values of the conduction and valence bands parallel and perpendicular to the c-axis. Self-organized hexagonal GaN pyramids of 5 μm width and covered by six {11̲01} side facets were investigated by spatially resolved cathodoluminescence and micro-Raman spectroscopy. Beside a narrow luminescence peak at 355 nm, originating from the 2 μm thick GaN layer, an additional broad luminescence band was observed from the GaN pyramids around a wavelength of 357 nm. A strong energy shift is found along the {11̲01} pyramidal facets and directly visualized by monochromatic cathodoluminescence images and line scans. In GaN epilayers grown on GaAs substrates a series of sharp modes in the range between 60 cm^{-1} and 250 cm^{-1} for temperatures below 100 K was found. The intensities of these modes increased drastically with decreasing temperature. Raman excitation spectra showed a maximum between 514.5 nm and 568 nm. A comparison of spatially resolved investigations with that of intentionally doped GaN epilayers showed that the in-diffusion of As from the substrate plays an important role. Raman spectra as a function of external fields, like magnetic field and hydrostatic pressure, gave additional information about the defect type and the underlying scattering mechanism.
15
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Characterization of Optical and Photoelectrical Properties of ZnO Crystals

51%
Onufrijevs P., Serevičius T., Scajev P., Manolis G., Medvids A., Chernyak L., Kuokstis E., Yang C., Jarasiunas K.
Acta Physica Polonica A
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2011
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vol. 119
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issue 2
274-276
EN
We characterized optical and photoelectrical properties of undoped and Ga-doped ZnO layers differently grown on sapphire substrates by using complementary optical methods. Different stimulated emission threshold values for ZnO epitaxial layers grown by pulsed laser deposition and MBE methods were attributed to crystalline quality of the layers and the growth method used. Different carrier lifetimes in various ZnO epitaxial layers are explained by defect-related and intrinsic mechanisms of recombination.
16
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The Time Dynamics Research of Coherent State in Semiconductors by Excitation of Femtoseconds Pulses

51%
Trukhin V., Buyskikh A.
Acta Physica Polonica A
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2011
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vol. 119
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issue 2
265-267
EN
In this article we present results of research of coherent processes of the ultrashort pulse light reemission in semiconductors. The time dynamics of the amplitude and the phase of the probe light wave reflected from the surface of low temperature GaAs was researched by the pump-probe method. The photodetector sensed the interference figure which shows interaction between probe pulse and pump pulse and also between probe pulse and excited by the pump coherent states in the semiconductor. The pulses wavelength is 800 nm and the pulses width is 15 fs. Thus the energy of excited photoelectrons was higher than conduction-band bottom by 60 to 140 meV. Due to the short duration of the pulse we could observe the coherent scattering of ultrashort light pulses at the room temperature. The impulse relaxation time for photoelectrons was determined by the experiments and it was 40 fs.
17
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LO-Phonon Band Filling by Means of Charge Carriers Accelerated in Electric Fields

45%
Raguotis R., Brazis R.
|
EN
Electron and phonon distribution in momentum space is modeled using Monte Carlo method. Calculated LO phonon distribution in zinc-blende GaN deviates dramatically from the thermal equilibrium (Planck) function, and well coincides with the phonon number elucidated from the existing anti-Stokes Raman scattering experiments.
18
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Optical Studies of Thermally Activated Vertical Hole Transport in ZnCdSe/ZnSSe Superlattice

45%
Lebedev A., Sorokin S., Toropov A., Shubina T., Il'inskaya N., Nekrutkina O., Ivanov S., Pozina G., Bergman P., Monemar B.
Acta Physica Polonica A
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1998
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vol. 94
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issue 3
421-426
EN
Miniband transport in alternatively-strained ZnCdSe/ZnSSe short period superlattices is investigated using a structure with an enlarged quantum well. Temperature dependences of time-resolved and continuous wave photoluminescence have been measured, demonstrating an efficient temperature-induced vertical hole transport. A quantitative description is given for the carrier kinetics in these structures.
19
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Resonant Cavity Enhanced Photonic Devices

38%
Bugajski M., Muszalski J., Ochalski T., Kątcki J., Mroziewicz B.
Acta Physica Polonica A
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2002
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vol. 101
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issue 1
105-118
EN
In the present paper we review our recent works on technology, basic physics, and applications of one-dimensional photonic structures. We demonstrate spontaneous emission control in In_xGa_{1-x}As/GaAs planar microcavities with distributed Bragg reflectors. In general, observed trends are in agreement with theoretical predictions. We also demonstrate the operation of resonant-cavity light emitting diodes and optically pumped vertical cavity light emitting diodes developed recently at the Department of Physics and Technology of Low-Dimensional Structures of the Institute of Electron Technology.
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