| 1. |
- Arnaudov, B, et al.
(författare)
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Energy position of near-band-edge emission spectra of InN epitaxial layers with different doping levels
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 69:11
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Tidskriftsartikel (refereegranskat)abstract
- We studied the shape and energy position of near-band-edge photoluminescence spectra of InN epitaxial layers with different doping levels. We found that the experimental spectra of InN layers with moderate doping level can be nicely interpreted in the frames of the "free-to-bound" recombination model in degenerate semiconductors. For carrier concentrations above n>5x10(18) cm(-3) the emission spectra can also be modeled satisfactorily, but a contribution due to a pushing up of nonequilibrium holes over the thermal delocalization level in the valence band tails should be considered in the model. The emission spectra of samples with low doping level were instead explained as a recombination from the bottom of the conduction band to a shallow acceptor assuming the same value of the acceptor binding energy estimated from the spectra of highly doped samples. Analyzing the shape and energy position of the free-electron recombination spectra we determined the carrier concentrations responsible for the emissions and found that the fundamental band gap energy of InN is E-g=692+/-2 meV for an effective mass at the conduction-band minimum m(n0)=0.042m(0).
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| 2. |
- Arnaudov, B., et al.
(författare)
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Free-to-bound radiative recombination in highly conducting InN epitaxial layers
- 2004
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Ingår i: Superlattices and Microstructures. - : Elsevier BV. - 0749-6036 .- 1096-3677. ; 36:4-6, s. 563-571
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Tidskriftsartikel (refereegranskat)abstract
- We present a theoretical simulation of near-band-edge emission spectra of highly conducting n-InN assuming the model of 'free-to-bound' radiative recombination (FBRR) of degenerate electrons from the conduction band with nonequilibrium holes located in the valence band tails. We also study experimental photoluminescence (PL) spectra of highly conducting InN epitaxial layers grown by MBE and MOVPE with electron concentrations in the range (7.7 × 1017-6 × 1018) cm-3 and find that the energy positions and shape of the spectra depend on the impurity concentration. By modeling the experimental PL spectra of the InN layers we show that spectra can be nicely interpreted in the framework of the FBRR model with specific peculiarities for different doping levels. Analyzing simultaneously the shape and energy position of the InN emission spectra we determine the fundamental bandgap energy of InN to vary between Eg = 692 meV for effective mass mn0 = 0.042m0 and Eg =710 meV for mn0 = 0.1m0. © 2004 Elsevier Ltd. All rights reserved.
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| 3. |
- Arnaudov, B, et al.
(författare)
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Hall effect data analysis of GaN n(+)n structures
- 2002
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Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 234:3, s. 872-876
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Tidskriftsartikel (refereegranskat)abstract
- We develop a model for analysis of Hall effect data of GaN structures composed of sublayers with different thicknesses and contacts placed on the top surface, We analysed the contributions of the conductivity of every sublayer of a planar sample taking into account the fact that the sample sublayers are partially connected in parallel to each other by series resistances formed in areas lying below the contacts from the upper layer. Correction factors, which reduce the contribution of the underlying layers to the measured whole sample conductivity, are obtained from the equations relevant to the respective equivalent circuit.
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| 4. |
- Arnaudov, B., et al.
(författare)
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Magnetic-field-induced localization of electrons in InGaN/GaN multiple quantum wells
- 2003
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 83:13, s. 2590-2592
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Tidskriftsartikel (refereegranskat)abstract
- A study was performed on the magnetic-field-induced localization of electrons in InGaN/GaN multiple quantum wells (MQW). A stepwise behavior of both the Hall coefficient and magnetoresistivity was observed. The peculiarities were explained by a magnetic-field-induced localization of electrons in a two-dimensional (2D) potential relief of the InGaN MQW.
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| 5. |
- Arnaudov, B, et al.
(författare)
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Modeling of the free-electron recombination band in emission spectra of highly conducting n-GaN
- 2001
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 64:4
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Tidskriftsartikel (refereegranskat)abstract
- We simulate the spectral distribution of the free-electron recombination band in optical emission spectra of GaN with a free-carrier concentration in the range of 5 x 10(17)-1 x 10(20) cm(-3). The influence of several factors, such as nonparabolicity, electron-electron interaction. and electron-impurity interaction on both the spectral and energy position and the effective gap narrowing are taken into account. The calculated properties of the free-electron-related emission bands are used to interpret the experimental photoluminescence and cathodoluminescence spectra of GaN epitaxial layers.
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| 6. |
- Arnaudov, B, et al.
(författare)
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Multilayer model for Hall effect data analysis of semiconductor structures with step-changed conductivity
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:4
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Tidskriftsartikel (refereegranskat)abstract
- We present a multilayer model for analysis of Hall effect data of semiconductor structures composed of sublayers with different thicknesses and contacts placed on the top surface. Based on the circuit theory we analyze the contributions of the conductivity of every sublayer and derive general expressions for the conductivity and carrier mobility of a multilayer planar sample. The circuit analysis is performed taking into account the fact that the sample sublayers are partially connected in parallel to each other by series resistances formed in areas lying below the contacts from each upper layer. In order to solve the inverse problem of determining the electrical parameters of one of the sublayers, a procedure for analysis of the Hall effect data is proposed. The model is simplified for a structure composed of two layers with the same type of conductivity, and is used to determine the electrical parameters of GaN films grown on relatively thick GaN buffers.
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| 7. |
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| 8. |
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| 9. |
- Darakchieva, Vanya, 1971-, et al.
(författare)
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Anisotropic strain and phonon deformation potentials in GaN
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:19, s. 195217-
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Tidskriftsartikel (refereegranskat)abstract
- We report optical phonon frequency studies in anisotropically strained c -plane- and a -plane-oriented GaN films by generalized infrared spectroscopic ellipsometry and Raman scattering spectroscopy. The anisotropic strain in the films is obtained from high-resolution x-ray diffraction measurements. Experimental evidence for splitting of the GaN E1 (TO), E1 (LO), and E2 phonons under anisotropic strain in the basal plane is presented, and their phonon deformation potentials c E1 (TO), c E1 (LO), and c E2 are determined. A distinct correlation between anisotropic strain and the A1 (TO) and E1 (LO) frequencies of a -plane GaN films reveals the a A1 (TO), b A1 (TO), a E1 (LO), and b E1 (LO) phonon deformation potentials. The a A1 (TO) and b A1 (TO) are found to be in very good agreement with previous results from Raman experiments. Our a A1 (TO) and a E1 (LO) phonon deformation potentials agree well with recently reported theoretical estimations, while b A1 (TO) and b E1 (LO) are found to be significantly larger than the theoretical values. A discussion of the observed differences is presented. © 2007 The American Physical Society.
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| 10. |
- Darakchieva, Vanya, et al.
(författare)
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Assessment of phonon mode characteristics via infrared spectroscopic ellipsometry on a-plane GaN
- 2006
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Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 243:7, s. 1594-1598
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Tidskriftsartikel (refereegranskat)abstract
- Generalized infrared spectroscopic ellipsometry was applied to study the vibrational properties of anisotropically strained a-plane GaN films with different thicknesses. We have established a correlation between the phonon mode parameters and the strain, which allows the determination of the deformation potentials and strain-free frequency of the GaN A,(TO) mode. These results are compared with previous theoretical and experimental findings and discussed.
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