| 1. |
- 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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| 2. |
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| 3. |
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| 4. |
- Darakchieva, Vanya, 1971-, et al.
(författare)
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Deformation potentials of the E1 (TO) and E2 modes of InN
- 2004
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 84:18, s. 3636-3638
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Tidskriftsartikel (refereegranskat)abstract
- The determination of deformation potentials of E1(TO) and E 2 modes of InN were discussed. The deformation potentials were evaluated for two sets of stiffness constants using x-ray diffraction, IR spectroscopic ellipsometry (IRSE), Raman scattering, and Grüneisen parameter values. The InN layer were grown on GaN buffer layers on (0001) sapphire by molecular beam epitaxy. It was found that the strain-free values of the InN E1(TO) mode was 477.9 cm-1 and 491.9 cm -1 for the E2 modes.
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| 5. |
- Darakchieva, Vanya, et al.
(författare)
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Electron accumulation at nonpolar and semipolar surfaces of wurtzite InN from generalized infrared ellipsometry
- 2009
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Ingår i: APPLIED PHYSICS LETTERS. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 95:20, s. 202103-
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Tidskriftsartikel (refereegranskat)abstract
- The free electron properties of nonpolar (1120)-oriented and semipolar (1011)-oriented wurtzite InN films are studied by generalized infrared ellipsometry (GIRSE). We demonstrate the sensitivity of GIRSE to the surface charge accumulation layer and find a distinct surface electron accumulation to occur at all surfaces. The obtained surface electron sheet densities are found to vary from 0.9x10(13) to 2.3x10(14) cm(-2) depending on the surface orientation and bulk electron concentration. The upper limits of the surface electron mobility parameters of 417-644 cm(2)/V s are determined and discussed in the light of electron confinement at the surface.
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| 6. |
- Darakchieva, Vanya, et al.
(författare)
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Free electron behavior in InN : On the role of dislocations and surface electron accumulation
- 2009
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 94:2, s. 022109-
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Tidskriftsartikel (refereegranskat)abstract
- The free electron behavior in InN is studied on the basis of decoupled bulk and surface accumulation electron densities in InN films measured by contactless optical Hall effect. It is shown that the variation in the bulk electron density with film thickness does not follow the models of free electrons generated by dislocation-associated nitrogen vacancies. This finding, further supported by transmission electron microscopy results, indicates the existence of a different thickness-dependent doping mechanism. Furthermore, we observe a noticeable dependence of the surface electron density on the bulk density, which can be exploited for tuning the surface charge in future InN based devices.
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| 7. |
- Darakchieva, Vanya, et al.
(författare)
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Hydrogen in InN: A ubiquitous phenomenon in molecular beam epitaxy grown material
- 2010
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Ingår i: APPLIED PHYSICS LETTERS. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 96:8, s. 081907-
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Tidskriftsartikel (refereegranskat)abstract
- We study the unintentional H impurities in relation to the free electron properties of state-of-the-art InN films grown by molecular beam epitaxy (MBE). Enhanced concentrations of H are revealed in the near surface regions of the films, indicating postgrowth surface contamination by H. The near surface hydrogen could not be removed upon thermal annealing and may have significant implications for the surface and bulk free electron properties of InN. The bulk free electron concentrations were found to scale with the bulk H concentrations while no distinct correlation with dislocation density could be inferred, indicating a major role of hydrogen for the unintentional conductivity in MBE InN.
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| 8. |
- Darakchieva, Vanya, et al.
(författare)
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Infrared ellipsometry and Raman studies of hexagonal InN films : Correlation between strain and vibrational properties
- 2004
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Ingår i: Superlattices and Microstructures. - : Elsevier BV. - 0749-6036 .- 1096-3677. ; 36:4-6, s. 573-580
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Tidskriftsartikel (refereegranskat)abstract
- The vibrational properties of InN films with different strain have been studied using Infrared ellipsometry and Raman scattering spectroscopy. We have established a correlation between the phonon mode parameters and the strain, which allows the determination of the deformation potentials and the strain-free frequencies of the InN E1(TO) and E2 modes. The LO phonons and their coupling to the free-carrier plasmon excitations are also discussed in relation to the carrier concentration in the films. © 2004 Elsevier Ltd. All rights reserved.
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| 9. |
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| 10. |
- Darakchieva, Vanya, et al.
(författare)
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Role of impurities and dislocations for the unintentional n-type conductivity in InN
- 2009
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Ingår i: PHYSICA B-CONDENSED MATTER. - : Elsevier BV. - 0921-4526. ; 404:22, s. 4476-4481
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Tidskriftsartikel (refereegranskat)abstract
- We present a study on the role of dislocations and impurities for the unintentional n-type conductivity in high-quality InN grown by molecular beam epitaxy. The dislocation densities and H profiles in films with free electron concentrations in the low 10(17) cm(-1) and mid 10(18) cm(-3) range are measured, and analyzed in a comparative manner. It is shown that dislocations alone could not account for the free electron behavior in the InN films. On the other hand, large concentrations of H sufficient to explain, but exceeding substantially, the observed free electron densities are found. Furthermore, enhanced concentrations of H are revealed at the film surfaces, resembling the free electron behavior with surface electron accumulation. The low-conductive film was found to contain C and it is suggested that C passivates the H donors or acts as an acceptor, producing compensated material in this case. Therefore, it is concluded that the unintentional impurities play an important role for the unintentional n-type conductivity in InN. We suggest a scenario of H incorporation in InN that may reconcile the previously reported observations for the different role of impurities and dislocations for the unintentional n-type conductivity in InN.
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