| 1. |
- Donchev, V., et al.
(author)
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Optical properties of thick GaInAs(Sb)N layers grown by liquid-phase epitaxy
- 2017
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In: 19TH INTERNATIONAL SCHOOL ON CONDENSED MATTER PHYSICS (ISCMP): ADVANCES IN NANOSTRUCTURED CONDENSED MATTER: RESEARCH AND INNOVATIONS. - : IOP PUBLISHING LTD.
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Conference paper (peer-reviewed)abstract
- We present an experimental and theoretical study of GaInAs(Sb)N layers with thickness around 2 mu m, grown by liquid-phase epitaxy (LPE) on n-type GaAs substrates. The samples are studied by surface photovoltage (SPV) spectroscopy and by photoluminescence spectroscopy. A theoretical model for the band structure of Sb-containing dilute nitrides is developed within the semi-empirical tight-binding approach in the sp(3)d(5)s*s(N) parameterisation and is used to calculate the electronic structure for different alloy compositions. The SPV spectra measured at room temperature clearly show a red shift of the absorption edge with respect to the absorption of the GaAs substrate. The shifts are in agreement with theoretical calculations results obtained for In, Sb and N concentrations corresponding to the experimentally determined ones. Photoluminescence measurements performed at 300K and 2 K show a smaller red shift of the emission energy with respect to GaAs as compared to the SPV results. The differences are explained by a tail of slow defect states below the conduction band edge, which are probed by SPV, but are less active in the PL experiment.
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| 2. |
- Donchev, V., et al.
(author)
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Photoluminescence study of AlAs/GaAs superlattices containing enlarged wells
- 2000
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In: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 364:1, s. 224-227
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Journal article (peer-reviewed)abstract
- Photoluminescence (PL) spectra of MBE grown short-period AlAs/GaAs superlattices with one or two enlarged wells (5 and 12 nm) have been measured at 2 K. Sharp PL peaks corresponding to excitonic transitions between the lowest electron and heavy-hole states in the enlarged wells are observed. The excitonic transition energies are calculated by means of an envelope function based model, taking into account the exciton binding energies. The model incorporates a smooth potential at the interfaces, which is represented by a diffusion potential, the diffusion length being a parameter. The calculated and experimentally observed excitonic transition energies agree well if diffusion lengths of 3.5 and 4.5 monolayers are considered in the samples with and without a buffer layer, respectively. These values are consistent with the complicated nature of the growth kinetics and mechanisms of quantum heterostructures. The PL spectra reveal also complicated structures connected with the superlattice. Their qualitative discussion confirms the smooth potential model. Thus, an attempt is made to extend the analysis of complicated AlAs/GaAs heterostructures towards real interfaces, which is essential for advanced device fabrication.
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| 3. |
- Donchev, V., et al.
(author)
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Photoluminescene line-shape analysis in quantum wells embedded in superlattices
- 2001
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In: Materials science & engineering. C, biomimetic materials, sensors and systems. - 0928-4931 .- 1873-0191. ; 15:1-2, s. 75-77
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Journal article (peer-reviewed)abstract
- The temperature evolution of the main photoluminescence (PL) mechanisms, in GaAs quantum wells embedded in short-period AlAs/GaAs superlattices, is investigated. PL spectra are measured from 2 to 300 K. A detailed line-shape analysis of the PL peaks is performed by means of a statistical model, including both free exciton and free carrier recombination. The fits based on this model reproduce satisfactorily the experimental PL line shapes and allow to assess quantitatively the relative contributions of free excitons and free carriers to the radiative recombination at different temperatures. The results indicate the predominant role of free excitons in the radiative recombination up to room temperature, and are consistent with the mass action law. © 2001 Elsevier Science B.V. All rights reserved.
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| 4. |
- Milanova, M., et al.
(author)
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Investigation of LPE grown dilute nitride InGaAs(Sb)N layers for photovoltaic applications
- 2019
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In: 10TH JUBILEE CONFERENCE OF THE BALKAN PHYSICAL UNION. - : AMER INST PHYSICS. - 9780735418035
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Conference paper (peer-reviewed)abstract
- We report on LPE growth and characterization of dilute nitride InGaAs(Sb)N layers nearly lattice matched to GaAs. In order to obtain high quality epitaxial layers without phase separation low-temperature variant of LPE method has been used. The composition and crystalline quality of the grown InGaAs(Sb)N layers have been determined by energy dispersive X-ray microanalysis and X-ray diffraction methods. SEM and AFM measurements on grown samples revealed flat interfaces and surface roughness in the range 0.2 - 0.3 nm. In order to identify the N-bonding mechanism in the alloys and the nature of nitrogen related clusters IR absorption and Raman scattering spectroscopy have been applied. The optical band gap of the samples is studied by photoluminescence (PL) spectroscopy at low and room temperatures and by surface photovoltage (SPV) spectroscopy at room temperature. The SPV and PL spectra reveal a red shift of the absorption edge and PL peak position as compared to GaAs, as well as localized states near the conduction band minimum. However, the optical band gap bowing of the samples appears smaller with respect to the random alloy, which is explained by the short-range ordering favored by LPE growth at near-equilibrium conditions. Variable angle ellipsometry is applied to determine the spectral behavior of the complex refractive index and estimate the band gap energy of the samples.
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| 5. |
- Shtinkov, N., et al.
(author)
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Effect of non-abrupt interfaces in AlAs/GaAs superlattices with embedded GaAs quantum wells
- 2000
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In: Vacuum. - 0042-207X .- 1879-2715. ; 58:2, s. 561-567
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Journal article (peer-reviewed)abstract
- In the present paper, we investigate the effect of the non-abrupt interfaces on the electronic and optical properties of short-period AlAs/GaAs superlattices with embedded GaAs quantum wells. The lateral disorder and the component interdiffusion at the interfaces are averaged over the layer planes and are effectively represented by a diffusion concentration profile in the growth direction. The diffusion length LD is used as a parameter characterizing the degree of interface broadening. The electronic structure calculations are made using the sp3s* spin-dependent empirical tight-binding Hamiltonian, the virtual crystal approximation, and the surface Green function matching method. The dependencies of the lowest electron (E1), heavy hole (HH1), and light hole (LH1) bound states on the diffusion length are calculated for LD from 0 to 4 monolayers. It is found that the energies of the transitions (E1-HH1) and (E1-LH1) increase as LD increases. The results obtained are compared with photoluminescence data for MBE-grown samples. It is found that the degree of interface broadening depends on the growth temperature and on the sample geometry. The diffusion lengths calculated from the experimental data follow the expected trends, revealing a good qualitative agreement between theory and experiment.
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