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Arnaudov B.,Sofia University | Domanevskii D.S.,Belarusian National Technical University | Evtimova S.,Sofia University | Ivanov C.,Sofia University | Kakanakov R.,Central Laboratory of Applied Physics
Solid State Phenomena | Year: 2010

We investigate light emission spectra at different excitation levels of nanoscale thin InGaN film participating in an InGaN/GaN quantum well (QW) with heavily doped barriers for green and blue light emitting diodes (LEDs). We model the spectral shape and energy position in frames of the free electron recombination model created first for highly doped 3D direct gap III-V semiconductor films and applied for QWs at low excitation. The model accounts for the influence on the potential width of the QW of the random impurity potential of the doped barriers which penetrates into the QW. The blue shift at high excitation is supposed to be due to the filling of the conduction band with degenerate 2D nonequilibrium electrons. A structure in the emission bands is observed and it is assumed to be a result from step-like 2D density-of-states (DOS) in the QW. A good agreement is obtained between the calculated and experimental spectra assuming that the barriers are graded. © (2010) Trans Tech Publications. Source


Heikkinen V.,University of Helsinki | Aaltonen J.,Helsinki Institute of Physics | Walchli B.,University of Helsinki | Raikkonen H.,University of Helsinki | And 7 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011

Scanning White Light Interferometry (SWLI) allows surface characterization of MEMS components. With transparent samples SWLI can image multiple stacked layers. However, since silicon is opaque to visible wavelengths, only the top layer can be measured using visible light. We combined multiple infrared light emitting diodes (IR-LEDs) to achieve adjustable IR illumination. This allows simultaneous measurement of top and bottom surface topographies of silicon samples - such as MEMS membranes- using a SWLI equipped with an IR camera. This advances the state of the art of the field of MEMS characterization by allowing looking under membranes of these devices during operation. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE). Source


Milanova M.,Central Laboratory of Applied Physics | Vitanov P.,Bulgarian Academy of Science | Terziyska P.,Lakehead University | Koleva G.,Central Laboratory of Applied Physics | Popov G.,Central Laboratory of Applied Physics
Physica Status Solidi (C) Current Topics in Solid State Physics | Year: 2013

This paper presents the comparison of nitrogen incorporation in GaAsN and InGaAsN layers grown on GaAs substrate from Ga- and In-rich solution, respectively, by liquid-phase epitaxy. Polycrystalline GaN has been used as a source of nitrogen in two cases. The initial epitaxy temperature has been varied in the temperature range 600-550 °C. Nitrogen content in Ga1-xAsNx grown layers has been determined to be in the range 0.1-0.5%. Higher nitrogen incorporation efficiency has been found for quaternary InGaAsN layers grown under carefully chosen lattice matched conditions. The incorporation of nitrogen into GaAsN and InGaAsN layers has been study by vibrational mode absorption spectroscopy. Nitrogen-induced vibration mode near 472 cm-1 has been registered in GaAsN samples. Preferential In-N bonds and the formation of N-centred In3Ga1 clusters have been identified for lattice matched to GaAs epitaxial InGaAsN layers. Electrical properties of the samples have been characterized by temperature-dependent Hall effect measurements. Nominally undoped GaAsN and InGaAsN grown layers are n-type with Hall concentration about one order of magnitude higher in comparison to layers not containing nitrogen. Thermally activated increase in the free carrier concentration at temperatures higher than 150 K is observed which indicates the presence of N-related deep donor levels below dilute nitride conduction band edge. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Milanova M.,Central Laboratory of Applied Physics | Vitanov P.,Bulgarian Academy of Science | Terziyska P.,Lakehead University | Popov G.,Central Laboratory of Applied Physics | Koleva G.,Central Laboratory of Applied Physics
Journal of Crystal Growth | Year: 2012

Crystallographic and transport properties of nominally undoped and Sn-doped InGaAsN layers grown by low-temperature LPE have been studied and related to the growth conditions. In the case of lattice matching, flat and uniform mirror-like layers of 8-10 μm in thickness are obtained. The compositions of the layers under study have been determined by combination of X-ray microanalysis and X-ray diffraction methods to be In 0.035Ga 0.065As 0.086N 0.014. The lattice mismatch between layer and substrate Δa l/a s calculated from X-ray diffraction curves is less than-7×10 -4 for all samples. The layers grown at lower epitaxy temperatures exhibit the highest crystalline quality, better lattice match and better homogeneity. This is in good agreement with the results of morphological study by atomic force microscopy which show root mean-square surface roughness of 0.18 nm for the best layers. CV and Hall measurements reveal that intentionally undoped InGaAsN layers are n-type with free carrier concentration about one order of magnitude higher in comparison to layers not containing nitrogen and high electron mobility values over 2000 cm 2/Vs. A dramatic reduction in the free carrier concentration and slightly increase in mobility are observed for Sn-doped InGaAsN layers. © 2012 Elsevier B.V. All rights reserved. Source


Milanova M.,Central Laboratory of Applied Physics | Kakanakov R.,Central Laboratory of Applied Physics | Koleva G.,Central Laboratory of Applied Physics | Vitanov P.,Bulgarian Academy of Science | And 3 more authors.
Solid State Phenomena | Year: 2010

GaSb based III-V heterostuctures are attractive for optoelectronic devices such as midinfrared lasers, detectors, and thermophotovoltaics (TPVs). In this paper the growth and characterization of GaInAsSb and GaAlAsSb quaternary layers, lattice-matched to GaSb substrate, are reported, with a particular focus on these alloys for TPV devices. High-quality with a mirror-like surface morphology epilayers Ga1-x InxAsy Sb 1-y with In content x in the range 0.1-0.22 and Ga 1-xAlxAsySb1-y layers with Al content up to 0.3 in the solid are grown by Liquid-Phase Epitaxy (LPE) from In- and Ga-rich melt, respectively. The compositions of the quaternary compounds are determined by X-ray microanalysis. The crystalline quality of GaInAsSb/GaSb and GaAlAsSb/GaSb heterostuctures is studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. © (2010) Trans Tech Publications. Source

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