| 1. |
- 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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| 2. |
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| 3. |
- 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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| 4. |
- Darakchieva, Vanya, et al.
(författare)
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Unintentional incorporation of hydrogen in wurtzite InN with different surface orientations
- 2011
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 110:6, s. 063535-
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Tidskriftsartikel (refereegranskat)abstract
- We have studied hydrogen impurities and related structural properties in state-of-the-art wurtzite InN films with polar, nonpolar, and semipolar surface orientations. The effects of thermal annealing and chemical treatment on the incorporation and stability of H are also discussed. The near-surface and bulk hydrogen concentrations in the as-grown films increase when changing the surface orientation from (0001) to (000 (1) over bar) to (1 (1) over bar 01) and to (11 (2) over bar0), which may be associated with a decrease in the grain size and change of the growth mode from 2D to 3D. Thermal annealing at 350 degrees C in N(2) leads to a reduction of H concentrations and the intrinsic levels of bulk H are found to correlate with the structural quality and defects in the annealed films.
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| 5. |
- Lorenz, L, et al.
(författare)
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Hydrogen In Group‐III Nitrides: An Ion Beam Analysis Study
- 2011
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Ingår i: AIP Conference Proceedings, Volume 1336. - : AIP. - 9780735408913 ; , s. 310-313
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Konferensbidrag (refereegranskat)abstract
- The doping mechanisms of InN, a promising material for novel optoelectronic and electronic devices, are still not well understood. Unintentional hydrogen doping is one possibility that could explain the unintentional n‐type conductivity in high‐quality nominally undoped InN films. We measured a series of state‐of‐the‐art InN samples grown by molecular beam epitaxy with 2 MeV 4He‐ERDA and RBS, showing the presence of relatively high amounts of hydrogen not only at the surface, but also in a deeper layer. Strong depletion of hydrogen due to the analysing beam was observed and taken into account in the analysis. Here, we report on the details of the analysis and show how the results correlate with the free‐electron concentrations of the samples.
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| 6. |
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| 7. |
- Shubina, Tatiana, 1950-, et al.
(författare)
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Optical properties of InN related to surface plasmons
- 2005
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 202:14, s. 2633-2641
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Tidskriftsartikel (refereegranskat)abstract
- We report on the complex nature of infrared luminescence and absorption in InN films, which cannot be entirely explained by the concept of a conventional narrow-gap semiconductor. In particular, it concerns the detection of peaks near absorption edges by both thermally detected optical absorption and photoluminescence excitation spectroscopy and the observation of extraordinarily strong resonant enhancement of emission. To describe the experimental data a model is proposed, which takes into account surface plasmons in metal-like inclusions, modifying the optical properties of InN. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA,.
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| 8. |
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| 9. |
- Shubina, Tatiana, et al.
(författare)
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Surface-plasmon resonances in indium nitride with metal-enriched nano-particles
- 2006
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 288:2, s. 230-235
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Tidskriftsartikel (refereegranskat)abstract
- Plasmonic resonances in In-enriched nano-particles, spontaneously formed during growth, can dramatically modify optical properties of InN. Experimental support for this is provided from detailed studies of absorption and infrared emission in InN. In particular, thermally detected optical absorption and photoluminescence excitation spectroscopy reveal a peak below the region of strong absorption in InN. A higher-energy part of the infrared emission having a noticeable p-polarization is markedly enhanced with excitation along the surface. These peculiarities are discussed in terms of the Mie resonances, arising in metallic spheroids with different aspect ratio, and their coupling with recombining states, whose strength depends on energy separation between the states and the resonances. © 2005 Elsevier B.V. All rights reserved.
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| 10. |
- 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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| 11. |
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| 12. |
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| 13. |
- 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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| 14. |
- 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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| 15. |
- 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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| 16. |
- 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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| 17. |
- Darakchieva, Vanya, et al.
(författare)
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Unintentional incorporation of H and related structural and free-electron properties of c- and a-plane InN
- 2012
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Ingår i: PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE. - : Wiley-VCH Verlag Berlin. - 1862-6300. ; 209:1, s. 91-94
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we present a comprehensive study on the hydrogen impurity depth profiles in InN films with polar c-plane and nonpolar a-plane surface orientations in relation to their structural and free-electron properties. We find that the as-grown nonpolar films exhibit generally higher bulk and near-surface H concentrations compared to the polar InN counter-parts. The latter may be partly associated with a change in the growth mode from 2D to 3D and a decrease in the grain size. Thermal annealing leads to a reduction of H concentrations and the intrinsic H levels are influenced by the structural characteristics of the films. The factors allowing reduction of bulk H and free electron concentrations in a-plane films are discussed.
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| 18. |
- Darakchieva, Vanya, et al.
(författare)
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Unravelling the free electron behavior in InN
- 2008
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Ingår i: Optoelectronic and Microelectronic Materials and Devices, 2008. - : IEEE. - 9781424427161 ; , s. 90-97
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Konferensbidrag (refereegranskat)abstract
- Precise measurement of the optical Hall effect in InN using magneto-optical generalized ellipsometry at IR and THz wavelengths, allows us to decouple the surface accumulation and bulk electron densities in InN films by non-contact optical means and further to precisely measure the effective mass and mobilities for polarizations parallel and perpendicular to the optical axis. Studies of InN films with different thicknesses, free electron densities and surface orientations enable an intricate picture of InN free electron properties to emerge. Striking findings on the scaling factors of the bulk electron densities with film thickness further supported by transmission electron microscopy point to an additional thickness dependent doping mechanism unrelated to dislocations. Surface electron accumulation is observed to occur not only at polar but also at non-polar and semi-polar wurtzite InN, and zinc blende InN surfaces. The persistent surface electron density shows a complex behavior with bulk density and surface orientation. This behavior might be exploited for tuning the surface charge in InN.
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| 19. |
- Hofmann, T., et al.
(författare)
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Anisotropy of the Γ-point effective mass and mobility in hexagonal InN
- 2006
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - Weinheim, Germany : Wiley-VCH Verlagsgesellschaft. - 1610-1634 .- 1610-1642. ; 3:6, s. 1854-1857
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Tidskriftsartikel (refereegranskat)abstract
- We determine the anisotropic electron effective mass and mobility parameters in wurtzite InN thin films with free electron concentration Nfrom 1.8 × 1017 cm–3 to 9.5 × 1018 cm–3 using Infrared Magneto-optic Generalized Ellipsometry. The room-temperature measurements were carried out with magnetic fields up to 4.5 T. For the Γ-point we estimate m*⊥ = 0.047m0 and m*‖ = 0.039m0 for polarization perpendicular and parallel to the c -axis, respectively. Scattering by impurities or ionized donors may explain the decrease of mobility for polarization parallel to the c -axis from 1600 cm2/(Vs) to 800 cm2/(Vs) with increase in N , where the perpendicular mobility is further decreased, likely caused by additional grain boundary scattering.
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| 20. |
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| 21. |
- Hofmann, T., et al.
(författare)
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Optical hall effect in hexagonal InN
- 2008
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 37:5, s. 611-615
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of the optical Hall effect in naturally doped high-quality wurtzite-structure InN thin films by generalized ellipsometry reveal that both the surface and the interior (bulk) free electron densities decrease with power-law dependencies on the film thickness. We discover a significant deviation between the bulk electron and dislocation densities. This difference is attributed here to the existence of surface defects with activation mechanism different from bulk dislocations and identifies the possible origin of the so far persistent natural n-type conductivity in InN. We further quantify the anisotropy of the Gamma-point effective mass.
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| 22. |
- Xie, Mengyao, et al.
(författare)
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Assessing structural, free-charge carrier, and phonon properties of mixed-phase epitaxial films: The case of InN
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 90:19, s. 195306-
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Tidskriftsartikel (refereegranskat)abstract
- We develop and discuss appropriate methods based on x-ray diffraction and generalized infrared spectroscopic ellipsometry to identify wurtizte and zinc-blende polymorphs, and quantify their volume fractions in mixed-phase epitaxial films taking InN as an example. The spectral signatures occurring in the azimuth polarization (Muller matrix) maps of mixed-phase epitaxial InN films are discussed and explained in view of polymorphism (zinc-blende versus wurtzite), volume fraction of different polymorphs and their crystallographic orientation, and azimuth angle. A comprehensive study of the structural, phonon and free electron properties of zinc-blende InN films containing inclusions of wurtzite InN is also presented. Thorough analysis on the formation of the zinc-blende and wurtzite phases is given and the structural evolution with film thickness is discussed in detail. The phonon properties of the two phases are determined and discussed together with the determination of the bulk free-charge carrier concentration, and electron accumulation at the mixed-phase InN film surfaces.
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| 23. |
- Xie, Mengyao, et al.
(författare)
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Structural, free-charge carrier and phonon properties of zinc-blende and wurtizte polymorphs in InN epitaxial layers
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present a comprehensive study of the structural, phonon and free electron properties of zincblende InN films containing inclusion of wurtzite InN. Appropriate methods based on X-ray diffraction and Infrared spectroscopic ellipsometry to identify wurtizte and zinc-blende InN and quantify their phase ratio are developed and discussed. Thorough analysis on the formation of the cubic and wurtzite phases is presented and their evolution with film thickness is discussed in detail. The freecharge carrier and phonon properties of the two phases are discussed together with the determination of electron accumulation at the zinc-blende InN (001) and wurtzite (10̅11) surfaces.
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